Journal of Investigative Surgery, 27, 332–337, 2014 C 2014 Informa Healthcare USA, Inc. Copyright ISSN: 0894-1939 print / 1521-0553 online DOI: 10.3109/08941939.2014.929764
ORIGINAL ARTICLE
Ileal Glucose Infusion Leads to Increased Insulin Sensitivity and Decreased Blood Glucose Levels in Wistar Rats Vo Nguyen Trung, MD PhD,1,3 Hiroshi Yamamoto, MD PhD,1 Satoshi Murata, MD PhD,1 Atsukazu Kuwahara, DVM PhD,2 Tohru Tani, MD PhD1 1
Department of Surgery, Shiga University of Medical Science, Seta-Tsukinowa-cho, Otsu, Shiga, Japan 2 Laboratory of Physiology, Graduate School of Integrated Pharmaceutical and Nutritional Sciences & Institute for Environmental Sciences, University of Shizuoka, Yata, Suruga-ku, Shizuoka, Japan, 3 Department of Surgery, Ho Chi Minh city University of Medicine and Pharmacy, Vietnam
ABSTRACT Purpose of the study: Rerouting of nutrients and/or increasing nutrient delivery to the small intestine after Rouxen-Y gastric bypass may have important potential as a diabetes treatment modality. However, it is still important question which part of the gastrointestinal tract is the most important for control of glycemia. The aim of this study was to investigate the role of different segments of the gastrointestinal tract on glucose metabolism in the physiological state. Materials and Methods: Forty 12-week-old male Wistar rats were divided into the following four groups of 10 animals each: the gastrostomy group, the duodenostomy group, the jejunostomy group, and the ileostomy group. All rats were subjected to a glucose tolerance test by infusion of glucose via the surgically inserted tubes in the stomach (gastrostomy), in the duodenum (duodenostomy), in the jejunum (jejunostomy), or in the ileum (ileostomy). Plasma glucagon-like peptide-17–36 (GLP-17–36 ) and insulin levels during the glucose tolerance test were assayed and Matsuda index was calculated. Results: Ileostomy rats exhibited significantly lower glycemic excursions compared with gastrostomy, duodenostomy, and jejunostomy rats. Insulin and GLP-1 levels during the glucose tolerance test were significantly higher in duodenostomy and jejunostomy rats than in gastrostomy and ileostomy rats. Matsuda index was significantly higher in ileostomy rats than in duodenostomy and jejunostomy rats. Conclusion: Ileal glucose infusion leads to increased insulin sensitivity, further decreasing blood glucose levels. Keywords: glucagon-like peptide-1; insulin; gastrostomy; duodenostomy; jejunostomy; ileostomy
INTRODUCTION
resolution after bariatric surgery have not been precisely determined. Rerouting of nutrients and/or increasing nutrient delivery to the small intestine after Roux-en-Y gastric bypass may have important potential as a diabetes treatment modality because this anatomical rearrangement of the gastrointestinal tract is believed to lead to the enhancement in glucagon-like peptide-1 (GLP-1) secretion, subsequently improving glucose tolerance [7–10]. However, it is still important question which segment of the gastrointestinal tract is the most important for control of glycemia. This animal study was conducted to investigate the role of different segments of the gastrointestinal tract on glucose metabolism.
Morbid obesity is a worldwide health problem because it promotes the development of various diseases such as cardiovascular disease and type 2 diabetes mellitus (T2DM), which greatly increases mortality [1]. Nonsurgical means-induced weight loss can improve insulin sensitivity, subsequently improving T2DM [2]. However, most patients still fail to achieve adequate weight loss and glycemic control with medical therapy. Bariatric surgery is currently the best option to achieve substantial and long-term weight loss and complete resolution of T2DM in morbidly obese patients with T2DM [3–6]. However, the exact mechanisms of T2DM
Received 12 March 2014; accepted 27 May 2014. Address correspondence to Hiroshi Yamamoto, MD, PhD, Department of Surgery, Shiga University of Medical Science, Seta-Tsukinowa-cho, Otsu, Shiga 520-2192, Japan. E-mail: [email protected]
332
Ileal Glucose Infusion Specifically, blood glucose, plasma GLP-17–36 , and insulin levels, and insulin sensitivity were compared between the stomach, duodenum, jejunum, and ileum after direct infusion of glucose into these organs.
MATERIALS AND METHODS Animals Forty 12-week-old male Wistar rats were housed in individual cages with constant ambient temperature and humidity and a 12-h light/dark cycle. The rats were fed with standard rat chow and allowed to acclimatize for a week before being subjected to surgery. The protocol was approved by the Committee on the Ethics of Animal Experiments of Shiga University of Medical Science, Shiga, Japan. All surgeries were performed under sevoflurane anesthesia, and all efforts were made to minimize suffering.
Surgical Procedures The rats were anesthetized by masking with 3% sevoflurane mixed with medical air (20% Oxygen, 80% Nitrogen) at a flow rate of 2 L/min. Penicillin (20.000 units/kg, Nacalai Tesque, Inc., Kyoto, Japan) was administered intramuscularly 30 min before operation. The rats were randomly divided into the following four groups of 10 animals each: the gastrostomy group, the duodenostomy group, the jejunostomy group, and the ileostomy group. Following anesthesia with sevoflurane, laparotomy was performed and 4-Fr Atom multipurpose tubes (Atom Medical Corporation, Tokyo, Japan) were inserted into the stomach (gastrostomy), the duodenum 1 cm distal to the pylorus (duodenostomy), the jejunum 5 cm distal to the ligament of Treitz (jejunostomy), or the ileum 25 cm proximal to the ileocecal valve (ileostomy) (Figure 1). The tubes were exteriorized at the back of the neck, and the abdominal wall was closed in layers using a running suture. All
FIGURE 1 Schematic illustration of gastrostomy, duodenostomy, jejunostomy, and ileostomy procedure. C
2014 Informa Healthcare USA, Inc.
333
procedures were performed under sterilized condition, antibiotics and analgesics were not used after surgery.
Postoperative Care Following surgery, the rats were fed ad libitum with normal chow. In order to decrease the effects of surgical stress on study parameters, the rats were followed for 1 week before being subjected to the glucose tolerance test.
Outcome Measures Glucose Tolerance Test The rats were made to fast overnight. At 08:00 h, glucose tolerance tests were performed in conscious rats by infusion of 50% glucose solution (1.5 g/kg) via the surgically inserted tubes. The infusates were left running into the gut at an estimated rate of infusion of approximately 0.5 mL/min to avoid excessive distension. And 150 μL of blood was collected into a tube containing aprotinin within 15 sec through a femoral vein catheter at 0, 10, 30, 60, 120, and 180 min after glucose infusion. The specimens were centrifuged and plasma samples were stored at −80◦ C until hormone assays were conducted. Hormone Assays Plasma insulin levels were assayed at 0, 10, 30, 60, and 120 min using enzyme-linked immunosorbent assay kits from the Morinaga Institute of Biological Science (Yokohama, Japan). We performed all the determination in duplicate. Insulin is a pancreatic hormone produced in the islets of Langerhans with a molecular weight of 5808 Da and it is composed of 51 amino acid residues. Insulin has long been known to increase glucose utilization by enhancing glucose uptake by liver, muscle, and fat. Fasting plasma insulin levels and plasma insulin levels during oral glucose tolerance test (OGTT) may be used to determine the whole-body insulin sensitivity [11]. Plasma GLP-17–36 and insulin levels were assayed at 0, 10, 30, 60, and 120 min using enzyme-linked immunosorbent assay kits from the Yanaihara Institute (Shizuoka, Japan). We performed all the determination in duplicate. GLP-1 is a peptide hormone that is released by enteroendocrine L cells in the intestine and that is supposed to improved glycemic control in patients with type 2 diabetes by increasing insulin secretion, by inhibiting glucagon secretion and by delaying gastric emptying rather than by altering extra pancreatic glucose metabolism. GLP-1 is responsible for nearly half of the total insulin secretion that occurs after meal [12, 13]. Insulin Sensitivity Whole-body insulin sensitivity was estimated using the Matsuda index, which was calculated using
334
V. N. Trung et al.
FIGURE 2 Blood glucose, insulin, and GLP-1 excursion after glucose infusion into different segments of the gastrointestinal tract. Data are shown as mean ± standard deviation. a: gastrostomy, b: duodenostomy, c: jejunostomy, and d: ileostomy. GLP-1: glucagon-like peptide-1.
the following formula: Matsuda index = 10,000/ [fasting plasma glucose concentration (mg/dL) × fasting plasma insulin concentration (mIU/L) × mean plasma glucose concentration during the first 120 min of the glucose tolerance test (mg/dL) × mean plasma insulin concentration during the first 120 min of the glucose tolerance test (mIU/L)]. By using the data available from the OGTT, Matsuda have developed a new index of whole-body insulin sensitivity that represents a composite of hepatic and peripheral tissues and considers insulin sensitivity in the basal state (fasting plasma glucose × fasting plasma insulin) and after the ingestion of a glucose load (mean plasma insulin × mean plasma glucose) [11]. Especially, Matsuda have shown that this index correlated strongly with the direct measure of insulin sensitivity derived from the euglycemic insulin clamp and suggested that the OGTT can be used effectively to define insulin sensitivity and secretory defects in individuals with impaired glucose homeostasis.
Statistical Analysis Data were analyzed using the Statistical Package for the Social Sciences software version 17.0 (SPSS Inc.,
Chicago, IL, USA). The one-way mixed-model analysis of variance test was used where appropriate. Significant differences between treatments were followed up with the Bonferroni multiple comparisons test. In all cases, statistical significance was set at p < .05, and the data were presented as means ± standard deviations. The area under the curve (AUC) from 0 to 180 min for glucose was calculated by trapezoidal integration. The AUC for GLP-1 and insulin was similarly calculated from 0 to 120 min.
RESULTS Glucose, Insulin, and GLP-1 Responses to Glucose Stimulation Basal glucose levels were identical in the four groups (55∼60 mg/dL) (Figure 2a–d). Blood glucose levels increased and reached the peak values at 10 min after glucose stimulation in gastrostomy rats (156 mg/dL) and duodenostomy rats (168 mg/dL) (Figure 2a–b). Jejunostomy rats showed a similar peak value (180 mg/dL) but needed longer time to reach the peak value compared with gastrostomy and duodenostomy rats; the peak value was obtained at 30 min after Journal of Investigative Surgery
Ileal Glucose Infusion glucose infusion into the jejunum (Figure 2c). On the other hand, ileostomy rat showed different pattern of blood glucose levels compared with other three groups; blood glucose levels reached the peak value at 30 min after glucose infusion but the peak value (130 mg/dL) was significantly lower than that of other three groups (Figure 2d). Furthermore, AUC for glucose in ileostomy group was significantly lower than that in the other groups (p = .009, Figure 3a). Fasting plasma insulin levels were similar between the four groups (0.13–0.15 ng/mL) (Figure 2a–d). The pattern of early insulin response at 10 and 30 min after glucose infusion was similar between duodenostomy and jejunostomy rats and between
335
gastrostomy and ileostomy rats (Figure 2a–d). Insulin levels in duodenostomy and jejunostomy rats reached the peak values at 30 min after glucose infusion and the peak values were significantly higher compared with those in gastrostomy and ileostomy rats (Figure 2a–d). Furthermore, AUC for plasma insulin was significantly higher in duodenostomy and jejunostomy rats compared with other two groups (p = .002, Figure 3b). Fasting GLP-1 levels were not different between the four groups (4.1∼4.8 ng/mL) (Figure 2a–d). After glucose infusion, GLP-1 levels in both duodenostomy and jejunostomy rats reached the peak values at 30 min (Figure 2b–c), whereas GLP-1 levels did not change in both gastrostomy and ileostomy rats after glucose infusion; lower GLP-1 levels were maintained over two hours in gastrostomy and ileostomy rats (Figure 2a,d). The peak GLP-1 levels were significantly higher in duodenostomy and jejunostomy rats than those in gastrostomy and ileostomy rats (Figure 2a–d). Furthermore, total GLP-1 responses to glucose stimulation were significantly higher in duodenostomy and jejunostomy rats compared with those in gastrostomy and ileostomy rats (p = .000, Figure 3c). Coefficient of variation (CV) values for all measurements were 11.02∼14.95%.
Whole-Body Insulin Sensitivity During Glucose Tolerance Test Matsuda index values were significantly higher in ileostomy (18.16 ± 1.33) rats than in duodenostomy (11.34 ± 2.84) and jejunostomy (13.72 ± 1.61) rats, indicating higher insulin sensitivity during the glucose tolerance test in ileostomy rats (p = .002). There was no significant difference in Matsuda index between gastrostomy group (15.64 ± 3.77) and the other groups.
DISCUSSION
FIGURE 3 AUC of blood glucose, insulin, and GLP-1 levels during the glucose tolerance test at different segments of the gastrointestinal tract a: blood glucose, b: insulin, and c: GLP-1. Data are shown as mean ± standard deviation. ∗ p < 0.05. GLP-1: glucagon-like peptide-1, AUC: area under the curve. C
2014 Informa Healthcare USA, Inc.
GLP-1, produced from post-translational modification of proglucagon, is secreted by intestinal L-cells which are located throughout the intestine with continuous increase of cell density from the distal jejunum to the distal ileum [14]. The mechanisms by which GLP-1 levels increase after gastric bypass surgery are not fully understood. Studies have postulated that rerouting of food through an anatomically altered gastrointestinal tract after gastric bypass surgery results in changes in GLP-1 levels [15–17]. Two main hypotheses have been proposed to explain the early effects of gastric bypass surgery on GLP-1 secretion – the hindgut hypothesis and the foregut hypothesis. The hindgut hypothesis states that the more rapid delivery of nutrients to the distal small intestine stimulates ileal L-cells, subsequently increasing GLP-1 secretion from these cells
336
V. N. Trung et al.
[18–20]; whereas the foregut hypothesis contends that exclusion of the proximal small intestine suppresses secretion of the anti-incretin factor, leading to increased incretin and insulin levels [9, 21]. Our findings may be partly explained by the foregut hypothesis. This hypothesis posits the existence of a nutrient-stimulated factor originating in the proximal small intestine, which is capable of decreasing insulin sensitivity and/or decreasing insulin secretion to compensate for the incretin-induced enhancement of insulin secretion, ultimately preventing postprandial hypoglycemia [21, 22]. In the present study, the fact that acute infusion of glucose in the duodenum or proximal jejunum (overstimulating these segments of the gastrointestinal tract) resulted in higher glycemic excursions in duodenostomy or jejunostomy rats than in ileostomy rats despite higher GLP-1 and insulin secretion suggests a relative inefficacy of these substances in this condition. Indeed, Matsuda index in duodenostomy and jejunostomy rats was significantly lower than in ileostomy rats, indicating increased insulin sensitivity in ileostomy rats. In support of the foregut hypothesis, we postulate that ileal glucose infusion, which bypasses the duodenum and jejunum, may prevent stimulation of the anti-incretin factor, further increasing insulin sensitivity. On the other hand, the hyperglycemia after duodenal/jejunal infusion may also be due to greater absorption of glucose and the bypass of the proximal bowel in ileostomy rats may also reduce glucose absorption, which could, at least in theory, improve postprandial glucose levels. Indeed, intestinal malabsorption resulting from the diversion of biliopancreatic juices into the terminal ileum has also been proposed as an alternative hypothesis for the control of diabetes after BPD [23]. However, limitations of our study do not allow to confirm or exclude this mechanism. Indeed, we did not investigate intestinal absorption and, on the other hand, important changes of the dynamic of other gastrointestinal hormones response to glucose might have been overlooked by testing only insulin and GLP-1 as we did. In the present study, we found the differences in GLP-1 levels between duodenostomy and gastrostomy rats although it seemed that glucose in these two instances followed the same route. However, in duodenostomy rats, glucose-induced stimulation of duodenum happens immediately with whole amount of glucose infusate; whereas in gastrostomy rats, this may happen later with smaller amount of glucose infusate due to the role of pylorus. This difference may lead to the differences in GLP-1 levels through stimulation of anti-incretin factor. In addition to foregut hypothesis, the enhanced GLP-1 secretion after gastric bypass surgery may be explained by the hindgut hypothesis, which indicates that the more rapid delivery of nutrients to the distal small intestine stimulates ileal L-cells, subsequently increasing GLP-1 secretion from these cells [8, 24].
However, the lack of enhancement in GLP-1 secretion by ileal glucose infusion in the present study suggests that rapid delivery of glucose to distal intestine may not fully explain the enhancement of GLP-1 secretion observed after gastric bypass. In addition, Patel RT reported that duodenal–jejunal bypass reduced blood glucose levels without changes in postprandial levels of insulin and GLP-1 in rats [25]. However, we showed here the GLP-1 responses to glucose stimulation in the physiological state, further studies using this model in diabetic or obese rats are needed to confirm this finding. Other explanations of lower glycemic excursion in ileostomy rats are possible. Troy [26] demonstrated that duodenal–jejunal bypass promoted intestinal gluconeogenesis and stimulated the hepatoportal glucose sensor via a glucose transporter 2-dependent pathway. This procedure quickly modified food intake and insulin sensitivity of hepatic glucose production, independent of GLP-1 levels. This finding can partly explain the difference in glucose tolerance without difference in GLP-1 and insulin secretion between gastrostomy and ileostomy rats in our study. In our experiment, we used OGTT in order to highlight the differences in glycemic, GLP-1, and insulin response, instead of mixed meal test which might have been a more physiologically relevant challenge than OGTT. However, in our clinical study of bariatric surgery, we usually use OGTT to examine the diabetes resolution after surgery. Thus, we would like to keep the same condition of glucose challenge in our experimental study. In addition, to avoid the effects of gut distension and duodenal gastric reflux, the rate of glucose infusion was controlled by leaving the infusates running into the gut at an estimated infusion rate of approximately 0.5 mL/min. Phillips et al. demonstrated that duodenal gastric reflux occurred only with intraduodenal infusions of >2.5 mL when infusates were delivered at a rate of 1 mL/min [27]. We acknowledge several limitations of this study. First, only normal physiological responses to glucose stimuli by different gastrointestinal segments were investigated. Therefore, studies evaluating these effects in diet-induced obese rats or diabetic rats must be conducted to extrapolate the findings of the current study to the mechanisms of bariatric surgery in obese or diabetic subjects. Lack of isotonic infusion of saline and lack of sham surgery in a group of control animals are other weak points of this study. Moreover, the overflow of carbohydrate infusate into the adjacent intestinal segments may affect our data. Therefore, other models of intestinal segment isolation including Thiry-Vella loop [28] or intraluminal balloon occlusion before infusion may render more accurate data. In addition, even though we carefully prepared samples to measure GLP-1 using dipeptidyl peptidase-4 inhibitor, the value of CV for GLP-1 in the present study is somewhat high because the active form of GLP-1 Journal of Investigative Surgery
Ileal Glucose Infusion is notoriously fragile and difficult to measure in a reliable manner. This indicates that our data has high variability and less stability. Thus, future studies using the same model with higher number of rats should be performed before generalization of our findings. Finally, direct intestinal infusion of glucose as performed in this study is unable to precisely reproduce the physiological response to glucose loading because it precludes involvement of bile and pancreatic juice. Despite the aforementioned limitations, our findings demonstrated that glycemic, GLP-1, and insulin responses to glucose loading are different between distinct segments of the gastrointestinal tract and that ileal glucose infusion, which bypasses the duodenum and jejunum, leads to increased insulin sensitivity, further decreasing blood glucose levels. Our findings advocated the foregut hypothesis in the mechanism underlying the effects of Roux-en-Y gastric bypass. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
REFERENCES [1] Mokdad AH, Bowman BA, Ford ES, et al. The continuing epidemics of obesity and diabetes in the United States. JAMA. 2001;286(10):1195–1200. [2] Sumithran P, Prendergast LA, Delbridge E, et al. Long-term persistence of hormonal adaptations to weight loss. N Engl J Med. 2011;365(17):1597–1604. [3] Cutolo PP, Nosso G, Vitolo G, et al. Clinical efficacy of laparoscopic sleeve gastrectomy vs laparoscopic gastric bypass in obese type 2 diabetic patients: a retrospective comparison. Obes Surg. 2012;22(10):1535–1539. [4] Jimenez A, Casamitjana R, Flores L, et al. Long-term effects of sleeve gastrectomy and Roux-en-Y gastric bypass surgery on type 2 diabetes mellitus in morbidly obese subjects. Ann Surg. 2012;256(6):1023–1029. [5] Peterli R, Steinert RE, Woelnerhanssen B, et al. Metabolic and hormonal changes after laparoscopic Roux-en-Y gastric bypass and sleeve gastrectomy: a randomized, prospective trial. Obes Surg. 2012;22(5):740–748. [6] Foschi D, Corsi F, Colombo F, et al. Different effects of vertical banded gastroplasty and Roux-en-Y gastric bypass on meal inhibition of ghrelin secretion in morbidly obese patients. J Invest Surg. 2008;21(2):77–81. [7] Araujo-Filho I, Rego AC, Azevedo IM, et al. Ileal Interposition and Viability of Pancreatic Islets Transplanted into Intramuscular Site of Diabetic Rats. J Invest Surg. 2013 Dec 30. In press. [8] Rubino F, Gagner M, Gentileschi P, et al. The early effect of the Roux-en-Y gastric bypass on hormones involved in body weight regulation and glucose metabolism. Ann Surg. 2004;240(2):236–242. [9] Rubino F, Marescaux J. Effect of duodenal-jejunal exclusion in a non-obese animal model of type 2 diabetes: a new perspective for an old disease. Ann Surg. 2004;239(1):1–11.
C
2014 Informa Healthcare USA, Inc.
337
[10] Sarson DL, Scopinaro N, Bloom SR. Gut hormone changes after jejunoileal (JIB) or biliopancreatic (BPB) bypass surgery for morbid obesity. Int J Obes. 1981;5(5):471–480. [11] Matsuda M, DeFronzo RA. Insulin sensitivity indices obtained from oral glucose tolerance testing: comparison with the euglycemic insulin clamp. Diabetes Care. 1999;22(9):1462–1470. [12] Holst JJ. The physiology of glucagon-like peptide 1. Physiol Rev. 2007;87(4):1409–1439. [13] Vella A, Shah P, Basu R, et al. Effect of glucagon-like peptide 1(7–36) amide on glucose effectiveness and insulin action in people with type 2 diabetes. Diabetes. 2000;49(4):611–617. [14] Eissele R, Goke R, Willemer S, et al. Glucagon-like peptide1 cells in the gastrointestinal tract and pancreas of rat, pig and man. Eur J Clin Invest. 1992;22(4):283–291. [15] Cohen RV, Pinheiro JC, Schiavon CA, et al. Effects of gastric bypass surgery in patients with type 2 diabetes and only mild obesity. Diabetes Care. 2012;35(7):1420–1428. [16] Lee WJ, Chong K, Ser KH, et al. Gastric bypass vs sleeve gastrectomy for type 2 diabetes mellitus: a randomized controlled trial. Arch Surg. 2011;146(2):143–148. [17] Zhu L, Mo Z, Yang X, et al. Effect of laparoscopic Rouxen-Y Gastroenterostomy with BMI < 35 kg/m(2) in type 2 diabetes mellitus. Obes Surg. 2012;22(10):1562–1567. [18] Karra E, Yousseif A, Batterham RL. Mechanisms facilitating weight loss and resolution of type 2 diabetes following bariatric surgery. Trends Endocrinol Metab. 2010;21(6):337–344. [19] Mingrone G, Castagneto-Gissey L. Mechanisms of early improvement/resolution of type 2 diabetes after bariatric surgery. Diabetes Metab. 2009;35(6 Pt 2):518–523. [20] Patriti A, Aisa MC, Annetti C, et al. How the hindgut can cure type 2 diabetes. Ileal transposition improves glucose metabolism and beta-cell function in Goto-kakizaki rats through an enhanced Proglucagon gene expression and Lcell number. Surgery. 2007;142(1):74–85. [21] Rubino F, R’Bibo S L, del Genio F, et al. Metabolic surgery: the role of the gastrointestinal tract in diabetes mellitus. Nat Rev Endocrinol. 2010;6(2):102–109. [22] Rubino F, Gagner M. Potential of surgery for curing type 2 diabetes mellitus. Ann Surg. 2002;236(5):554–559. [23] Mingrone G, DeGaetano A, Greco AV, et al. Reversibility of insulin resistance in obese diabetic patients: role of plasma lipids. Diabetologia. 1997;40(5):599–605. [24] Peterli R, Wolnerhanssen B, Peters T, et al. Improvement in glucose metabolism after bariatric surgery: comparison of laparoscopic Roux-en-Y gastric bypass and laparoscopic sleeve gastrectomy: a prospective randomized trial. Ann Surg. 2009;250(2):234–241. [25] Patel RT, Shukla AP, Ahn SM, et al. Surgical control of obesity and diabetes: the role of intestinal vs. gastric mechanisms in the regulation of body weight and glucose homeostasis. Obesity (Silver Spring). 2014;22(1):159–169. [26] Troy S, Soty M, Ribeiro L, et al. Intestinal gluconeogenesis is a key factor for early metabolic changes after gastric bypass but not after gastric lap-band in mice. Cell Metab. 2008;8(3):201–211. [27] Phillips RJ, Walls EK, Powley TL. Duodenogastric reflux of intestinal infusions in rats is volume dependent. Appetite. 1996;27(1):79–90. [28] Stearns AT, Balakrishnan A, Rhoads DB, et al. Diurnal expression of the rat intestinal sodium-glucose cotransporter 1 (SGLT1) is independent of local luminal factors. Surgery. 2009;145(3):294–302.
Copyright of Journal of Investigative Surgery is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
ORIGINAL ARTICLE
Ileal Glucose Infusion Leads to Increased Insulin Sensitivity and Decreased Blood Glucose Levels in Wistar Rats Vo Nguyen Trung, MD PhD,1,3 Hiroshi Yamamoto, MD PhD,1 Satoshi Murata, MD PhD,1 Atsukazu Kuwahara, DVM PhD,2 Tohru Tani, MD PhD1 1
Department of Surgery, Shiga University of Medical Science, Seta-Tsukinowa-cho, Otsu, Shiga, Japan 2 Laboratory of Physiology, Graduate School of Integrated Pharmaceutical and Nutritional Sciences & Institute for Environmental Sciences, University of Shizuoka, Yata, Suruga-ku, Shizuoka, Japan, 3 Department of Surgery, Ho Chi Minh city University of Medicine and Pharmacy, Vietnam
ABSTRACT Purpose of the study: Rerouting of nutrients and/or increasing nutrient delivery to the small intestine after Rouxen-Y gastric bypass may have important potential as a diabetes treatment modality. However, it is still important question which part of the gastrointestinal tract is the most important for control of glycemia. The aim of this study was to investigate the role of different segments of the gastrointestinal tract on glucose metabolism in the physiological state. Materials and Methods: Forty 12-week-old male Wistar rats were divided into the following four groups of 10 animals each: the gastrostomy group, the duodenostomy group, the jejunostomy group, and the ileostomy group. All rats were subjected to a glucose tolerance test by infusion of glucose via the surgically inserted tubes in the stomach (gastrostomy), in the duodenum (duodenostomy), in the jejunum (jejunostomy), or in the ileum (ileostomy). Plasma glucagon-like peptide-17–36 (GLP-17–36 ) and insulin levels during the glucose tolerance test were assayed and Matsuda index was calculated. Results: Ileostomy rats exhibited significantly lower glycemic excursions compared with gastrostomy, duodenostomy, and jejunostomy rats. Insulin and GLP-1 levels during the glucose tolerance test were significantly higher in duodenostomy and jejunostomy rats than in gastrostomy and ileostomy rats. Matsuda index was significantly higher in ileostomy rats than in duodenostomy and jejunostomy rats. Conclusion: Ileal glucose infusion leads to increased insulin sensitivity, further decreasing blood glucose levels. Keywords: glucagon-like peptide-1; insulin; gastrostomy; duodenostomy; jejunostomy; ileostomy
INTRODUCTION
resolution after bariatric surgery have not been precisely determined. Rerouting of nutrients and/or increasing nutrient delivery to the small intestine after Roux-en-Y gastric bypass may have important potential as a diabetes treatment modality because this anatomical rearrangement of the gastrointestinal tract is believed to lead to the enhancement in glucagon-like peptide-1 (GLP-1) secretion, subsequently improving glucose tolerance [7–10]. However, it is still important question which segment of the gastrointestinal tract is the most important for control of glycemia. This animal study was conducted to investigate the role of different segments of the gastrointestinal tract on glucose metabolism.
Morbid obesity is a worldwide health problem because it promotes the development of various diseases such as cardiovascular disease and type 2 diabetes mellitus (T2DM), which greatly increases mortality [1]. Nonsurgical means-induced weight loss can improve insulin sensitivity, subsequently improving T2DM [2]. However, most patients still fail to achieve adequate weight loss and glycemic control with medical therapy. Bariatric surgery is currently the best option to achieve substantial and long-term weight loss and complete resolution of T2DM in morbidly obese patients with T2DM [3–6]. However, the exact mechanisms of T2DM
Received 12 March 2014; accepted 27 May 2014. Address correspondence to Hiroshi Yamamoto, MD, PhD, Department of Surgery, Shiga University of Medical Science, Seta-Tsukinowa-cho, Otsu, Shiga 520-2192, Japan. E-mail: [email protected]
332
Ileal Glucose Infusion Specifically, blood glucose, plasma GLP-17–36 , and insulin levels, and insulin sensitivity were compared between the stomach, duodenum, jejunum, and ileum after direct infusion of glucose into these organs.
MATERIALS AND METHODS Animals Forty 12-week-old male Wistar rats were housed in individual cages with constant ambient temperature and humidity and a 12-h light/dark cycle. The rats were fed with standard rat chow and allowed to acclimatize for a week before being subjected to surgery. The protocol was approved by the Committee on the Ethics of Animal Experiments of Shiga University of Medical Science, Shiga, Japan. All surgeries were performed under sevoflurane anesthesia, and all efforts were made to minimize suffering.
Surgical Procedures The rats were anesthetized by masking with 3% sevoflurane mixed with medical air (20% Oxygen, 80% Nitrogen) at a flow rate of 2 L/min. Penicillin (20.000 units/kg, Nacalai Tesque, Inc., Kyoto, Japan) was administered intramuscularly 30 min before operation. The rats were randomly divided into the following four groups of 10 animals each: the gastrostomy group, the duodenostomy group, the jejunostomy group, and the ileostomy group. Following anesthesia with sevoflurane, laparotomy was performed and 4-Fr Atom multipurpose tubes (Atom Medical Corporation, Tokyo, Japan) were inserted into the stomach (gastrostomy), the duodenum 1 cm distal to the pylorus (duodenostomy), the jejunum 5 cm distal to the ligament of Treitz (jejunostomy), or the ileum 25 cm proximal to the ileocecal valve (ileostomy) (Figure 1). The tubes were exteriorized at the back of the neck, and the abdominal wall was closed in layers using a running suture. All
FIGURE 1 Schematic illustration of gastrostomy, duodenostomy, jejunostomy, and ileostomy procedure. C
2014 Informa Healthcare USA, Inc.
333
procedures were performed under sterilized condition, antibiotics and analgesics were not used after surgery.
Postoperative Care Following surgery, the rats were fed ad libitum with normal chow. In order to decrease the effects of surgical stress on study parameters, the rats were followed for 1 week before being subjected to the glucose tolerance test.
Outcome Measures Glucose Tolerance Test The rats were made to fast overnight. At 08:00 h, glucose tolerance tests were performed in conscious rats by infusion of 50% glucose solution (1.5 g/kg) via the surgically inserted tubes. The infusates were left running into the gut at an estimated rate of infusion of approximately 0.5 mL/min to avoid excessive distension. And 150 μL of blood was collected into a tube containing aprotinin within 15 sec through a femoral vein catheter at 0, 10, 30, 60, 120, and 180 min after glucose infusion. The specimens were centrifuged and plasma samples were stored at −80◦ C until hormone assays were conducted. Hormone Assays Plasma insulin levels were assayed at 0, 10, 30, 60, and 120 min using enzyme-linked immunosorbent assay kits from the Morinaga Institute of Biological Science (Yokohama, Japan). We performed all the determination in duplicate. Insulin is a pancreatic hormone produced in the islets of Langerhans with a molecular weight of 5808 Da and it is composed of 51 amino acid residues. Insulin has long been known to increase glucose utilization by enhancing glucose uptake by liver, muscle, and fat. Fasting plasma insulin levels and plasma insulin levels during oral glucose tolerance test (OGTT) may be used to determine the whole-body insulin sensitivity [11]. Plasma GLP-17–36 and insulin levels were assayed at 0, 10, 30, 60, and 120 min using enzyme-linked immunosorbent assay kits from the Yanaihara Institute (Shizuoka, Japan). We performed all the determination in duplicate. GLP-1 is a peptide hormone that is released by enteroendocrine L cells in the intestine and that is supposed to improved glycemic control in patients with type 2 diabetes by increasing insulin secretion, by inhibiting glucagon secretion and by delaying gastric emptying rather than by altering extra pancreatic glucose metabolism. GLP-1 is responsible for nearly half of the total insulin secretion that occurs after meal [12, 13]. Insulin Sensitivity Whole-body insulin sensitivity was estimated using the Matsuda index, which was calculated using
334
V. N. Trung et al.
FIGURE 2 Blood glucose, insulin, and GLP-1 excursion after glucose infusion into different segments of the gastrointestinal tract. Data are shown as mean ± standard deviation. a: gastrostomy, b: duodenostomy, c: jejunostomy, and d: ileostomy. GLP-1: glucagon-like peptide-1.
the following formula: Matsuda index = 10,000/ [fasting plasma glucose concentration (mg/dL) × fasting plasma insulin concentration (mIU/L) × mean plasma glucose concentration during the first 120 min of the glucose tolerance test (mg/dL) × mean plasma insulin concentration during the first 120 min of the glucose tolerance test (mIU/L)]. By using the data available from the OGTT, Matsuda have developed a new index of whole-body insulin sensitivity that represents a composite of hepatic and peripheral tissues and considers insulin sensitivity in the basal state (fasting plasma glucose × fasting plasma insulin) and after the ingestion of a glucose load (mean plasma insulin × mean plasma glucose) [11]. Especially, Matsuda have shown that this index correlated strongly with the direct measure of insulin sensitivity derived from the euglycemic insulin clamp and suggested that the OGTT can be used effectively to define insulin sensitivity and secretory defects in individuals with impaired glucose homeostasis.
Statistical Analysis Data were analyzed using the Statistical Package for the Social Sciences software version 17.0 (SPSS Inc.,
Chicago, IL, USA). The one-way mixed-model analysis of variance test was used where appropriate. Significant differences between treatments were followed up with the Bonferroni multiple comparisons test. In all cases, statistical significance was set at p < .05, and the data were presented as means ± standard deviations. The area under the curve (AUC) from 0 to 180 min for glucose was calculated by trapezoidal integration. The AUC for GLP-1 and insulin was similarly calculated from 0 to 120 min.
RESULTS Glucose, Insulin, and GLP-1 Responses to Glucose Stimulation Basal glucose levels were identical in the four groups (55∼60 mg/dL) (Figure 2a–d). Blood glucose levels increased and reached the peak values at 10 min after glucose stimulation in gastrostomy rats (156 mg/dL) and duodenostomy rats (168 mg/dL) (Figure 2a–b). Jejunostomy rats showed a similar peak value (180 mg/dL) but needed longer time to reach the peak value compared with gastrostomy and duodenostomy rats; the peak value was obtained at 30 min after Journal of Investigative Surgery
Ileal Glucose Infusion glucose infusion into the jejunum (Figure 2c). On the other hand, ileostomy rat showed different pattern of blood glucose levels compared with other three groups; blood glucose levels reached the peak value at 30 min after glucose infusion but the peak value (130 mg/dL) was significantly lower than that of other three groups (Figure 2d). Furthermore, AUC for glucose in ileostomy group was significantly lower than that in the other groups (p = .009, Figure 3a). Fasting plasma insulin levels were similar between the four groups (0.13–0.15 ng/mL) (Figure 2a–d). The pattern of early insulin response at 10 and 30 min after glucose infusion was similar between duodenostomy and jejunostomy rats and between
335
gastrostomy and ileostomy rats (Figure 2a–d). Insulin levels in duodenostomy and jejunostomy rats reached the peak values at 30 min after glucose infusion and the peak values were significantly higher compared with those in gastrostomy and ileostomy rats (Figure 2a–d). Furthermore, AUC for plasma insulin was significantly higher in duodenostomy and jejunostomy rats compared with other two groups (p = .002, Figure 3b). Fasting GLP-1 levels were not different between the four groups (4.1∼4.8 ng/mL) (Figure 2a–d). After glucose infusion, GLP-1 levels in both duodenostomy and jejunostomy rats reached the peak values at 30 min (Figure 2b–c), whereas GLP-1 levels did not change in both gastrostomy and ileostomy rats after glucose infusion; lower GLP-1 levels were maintained over two hours in gastrostomy and ileostomy rats (Figure 2a,d). The peak GLP-1 levels were significantly higher in duodenostomy and jejunostomy rats than those in gastrostomy and ileostomy rats (Figure 2a–d). Furthermore, total GLP-1 responses to glucose stimulation were significantly higher in duodenostomy and jejunostomy rats compared with those in gastrostomy and ileostomy rats (p = .000, Figure 3c). Coefficient of variation (CV) values for all measurements were 11.02∼14.95%.
Whole-Body Insulin Sensitivity During Glucose Tolerance Test Matsuda index values were significantly higher in ileostomy (18.16 ± 1.33) rats than in duodenostomy (11.34 ± 2.84) and jejunostomy (13.72 ± 1.61) rats, indicating higher insulin sensitivity during the glucose tolerance test in ileostomy rats (p = .002). There was no significant difference in Matsuda index between gastrostomy group (15.64 ± 3.77) and the other groups.
DISCUSSION
FIGURE 3 AUC of blood glucose, insulin, and GLP-1 levels during the glucose tolerance test at different segments of the gastrointestinal tract a: blood glucose, b: insulin, and c: GLP-1. Data are shown as mean ± standard deviation. ∗ p < 0.05. GLP-1: glucagon-like peptide-1, AUC: area under the curve. C
2014 Informa Healthcare USA, Inc.
GLP-1, produced from post-translational modification of proglucagon, is secreted by intestinal L-cells which are located throughout the intestine with continuous increase of cell density from the distal jejunum to the distal ileum [14]. The mechanisms by which GLP-1 levels increase after gastric bypass surgery are not fully understood. Studies have postulated that rerouting of food through an anatomically altered gastrointestinal tract after gastric bypass surgery results in changes in GLP-1 levels [15–17]. Two main hypotheses have been proposed to explain the early effects of gastric bypass surgery on GLP-1 secretion – the hindgut hypothesis and the foregut hypothesis. The hindgut hypothesis states that the more rapid delivery of nutrients to the distal small intestine stimulates ileal L-cells, subsequently increasing GLP-1 secretion from these cells
336
V. N. Trung et al.
[18–20]; whereas the foregut hypothesis contends that exclusion of the proximal small intestine suppresses secretion of the anti-incretin factor, leading to increased incretin and insulin levels [9, 21]. Our findings may be partly explained by the foregut hypothesis. This hypothesis posits the existence of a nutrient-stimulated factor originating in the proximal small intestine, which is capable of decreasing insulin sensitivity and/or decreasing insulin secretion to compensate for the incretin-induced enhancement of insulin secretion, ultimately preventing postprandial hypoglycemia [21, 22]. In the present study, the fact that acute infusion of glucose in the duodenum or proximal jejunum (overstimulating these segments of the gastrointestinal tract) resulted in higher glycemic excursions in duodenostomy or jejunostomy rats than in ileostomy rats despite higher GLP-1 and insulin secretion suggests a relative inefficacy of these substances in this condition. Indeed, Matsuda index in duodenostomy and jejunostomy rats was significantly lower than in ileostomy rats, indicating increased insulin sensitivity in ileostomy rats. In support of the foregut hypothesis, we postulate that ileal glucose infusion, which bypasses the duodenum and jejunum, may prevent stimulation of the anti-incretin factor, further increasing insulin sensitivity. On the other hand, the hyperglycemia after duodenal/jejunal infusion may also be due to greater absorption of glucose and the bypass of the proximal bowel in ileostomy rats may also reduce glucose absorption, which could, at least in theory, improve postprandial glucose levels. Indeed, intestinal malabsorption resulting from the diversion of biliopancreatic juices into the terminal ileum has also been proposed as an alternative hypothesis for the control of diabetes after BPD [23]. However, limitations of our study do not allow to confirm or exclude this mechanism. Indeed, we did not investigate intestinal absorption and, on the other hand, important changes of the dynamic of other gastrointestinal hormones response to glucose might have been overlooked by testing only insulin and GLP-1 as we did. In the present study, we found the differences in GLP-1 levels between duodenostomy and gastrostomy rats although it seemed that glucose in these two instances followed the same route. However, in duodenostomy rats, glucose-induced stimulation of duodenum happens immediately with whole amount of glucose infusate; whereas in gastrostomy rats, this may happen later with smaller amount of glucose infusate due to the role of pylorus. This difference may lead to the differences in GLP-1 levels through stimulation of anti-incretin factor. In addition to foregut hypothesis, the enhanced GLP-1 secretion after gastric bypass surgery may be explained by the hindgut hypothesis, which indicates that the more rapid delivery of nutrients to the distal small intestine stimulates ileal L-cells, subsequently increasing GLP-1 secretion from these cells [8, 24].
However, the lack of enhancement in GLP-1 secretion by ileal glucose infusion in the present study suggests that rapid delivery of glucose to distal intestine may not fully explain the enhancement of GLP-1 secretion observed after gastric bypass. In addition, Patel RT reported that duodenal–jejunal bypass reduced blood glucose levels without changes in postprandial levels of insulin and GLP-1 in rats [25]. However, we showed here the GLP-1 responses to glucose stimulation in the physiological state, further studies using this model in diabetic or obese rats are needed to confirm this finding. Other explanations of lower glycemic excursion in ileostomy rats are possible. Troy [26] demonstrated that duodenal–jejunal bypass promoted intestinal gluconeogenesis and stimulated the hepatoportal glucose sensor via a glucose transporter 2-dependent pathway. This procedure quickly modified food intake and insulin sensitivity of hepatic glucose production, independent of GLP-1 levels. This finding can partly explain the difference in glucose tolerance without difference in GLP-1 and insulin secretion between gastrostomy and ileostomy rats in our study. In our experiment, we used OGTT in order to highlight the differences in glycemic, GLP-1, and insulin response, instead of mixed meal test which might have been a more physiologically relevant challenge than OGTT. However, in our clinical study of bariatric surgery, we usually use OGTT to examine the diabetes resolution after surgery. Thus, we would like to keep the same condition of glucose challenge in our experimental study. In addition, to avoid the effects of gut distension and duodenal gastric reflux, the rate of glucose infusion was controlled by leaving the infusates running into the gut at an estimated infusion rate of approximately 0.5 mL/min. Phillips et al. demonstrated that duodenal gastric reflux occurred only with intraduodenal infusions of >2.5 mL when infusates were delivered at a rate of 1 mL/min [27]. We acknowledge several limitations of this study. First, only normal physiological responses to glucose stimuli by different gastrointestinal segments were investigated. Therefore, studies evaluating these effects in diet-induced obese rats or diabetic rats must be conducted to extrapolate the findings of the current study to the mechanisms of bariatric surgery in obese or diabetic subjects. Lack of isotonic infusion of saline and lack of sham surgery in a group of control animals are other weak points of this study. Moreover, the overflow of carbohydrate infusate into the adjacent intestinal segments may affect our data. Therefore, other models of intestinal segment isolation including Thiry-Vella loop [28] or intraluminal balloon occlusion before infusion may render more accurate data. In addition, even though we carefully prepared samples to measure GLP-1 using dipeptidyl peptidase-4 inhibitor, the value of CV for GLP-1 in the present study is somewhat high because the active form of GLP-1 Journal of Investigative Surgery
Ileal Glucose Infusion is notoriously fragile and difficult to measure in a reliable manner. This indicates that our data has high variability and less stability. Thus, future studies using the same model with higher number of rats should be performed before generalization of our findings. Finally, direct intestinal infusion of glucose as performed in this study is unable to precisely reproduce the physiological response to glucose loading because it precludes involvement of bile and pancreatic juice. Despite the aforementioned limitations, our findings demonstrated that glycemic, GLP-1, and insulin responses to glucose loading are different between distinct segments of the gastrointestinal tract and that ileal glucose infusion, which bypasses the duodenum and jejunum, leads to increased insulin sensitivity, further decreasing blood glucose levels. Our findings advocated the foregut hypothesis in the mechanism underlying the effects of Roux-en-Y gastric bypass. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
REFERENCES [1] Mokdad AH, Bowman BA, Ford ES, et al. The continuing epidemics of obesity and diabetes in the United States. JAMA. 2001;286(10):1195–1200. [2] Sumithran P, Prendergast LA, Delbridge E, et al. Long-term persistence of hormonal adaptations to weight loss. N Engl J Med. 2011;365(17):1597–1604. [3] Cutolo PP, Nosso G, Vitolo G, et al. Clinical efficacy of laparoscopic sleeve gastrectomy vs laparoscopic gastric bypass in obese type 2 diabetic patients: a retrospective comparison. Obes Surg. 2012;22(10):1535–1539. [4] Jimenez A, Casamitjana R, Flores L, et al. Long-term effects of sleeve gastrectomy and Roux-en-Y gastric bypass surgery on type 2 diabetes mellitus in morbidly obese subjects. Ann Surg. 2012;256(6):1023–1029. [5] Peterli R, Steinert RE, Woelnerhanssen B, et al. Metabolic and hormonal changes after laparoscopic Roux-en-Y gastric bypass and sleeve gastrectomy: a randomized, prospective trial. Obes Surg. 2012;22(5):740–748. [6] Foschi D, Corsi F, Colombo F, et al. Different effects of vertical banded gastroplasty and Roux-en-Y gastric bypass on meal inhibition of ghrelin secretion in morbidly obese patients. J Invest Surg. 2008;21(2):77–81. [7] Araujo-Filho I, Rego AC, Azevedo IM, et al. Ileal Interposition and Viability of Pancreatic Islets Transplanted into Intramuscular Site of Diabetic Rats. J Invest Surg. 2013 Dec 30. In press. [8] Rubino F, Gagner M, Gentileschi P, et al. The early effect of the Roux-en-Y gastric bypass on hormones involved in body weight regulation and glucose metabolism. Ann Surg. 2004;240(2):236–242. [9] Rubino F, Marescaux J. Effect of duodenal-jejunal exclusion in a non-obese animal model of type 2 diabetes: a new perspective for an old disease. Ann Surg. 2004;239(1):1–11.
C
2014 Informa Healthcare USA, Inc.
337
[10] Sarson DL, Scopinaro N, Bloom SR. Gut hormone changes after jejunoileal (JIB) or biliopancreatic (BPB) bypass surgery for morbid obesity. Int J Obes. 1981;5(5):471–480. [11] Matsuda M, DeFronzo RA. Insulin sensitivity indices obtained from oral glucose tolerance testing: comparison with the euglycemic insulin clamp. Diabetes Care. 1999;22(9):1462–1470. [12] Holst JJ. The physiology of glucagon-like peptide 1. Physiol Rev. 2007;87(4):1409–1439. [13] Vella A, Shah P, Basu R, et al. Effect of glucagon-like peptide 1(7–36) amide on glucose effectiveness and insulin action in people with type 2 diabetes. Diabetes. 2000;49(4):611–617. [14] Eissele R, Goke R, Willemer S, et al. Glucagon-like peptide1 cells in the gastrointestinal tract and pancreas of rat, pig and man. Eur J Clin Invest. 1992;22(4):283–291. [15] Cohen RV, Pinheiro JC, Schiavon CA, et al. Effects of gastric bypass surgery in patients with type 2 diabetes and only mild obesity. Diabetes Care. 2012;35(7):1420–1428. [16] Lee WJ, Chong K, Ser KH, et al. Gastric bypass vs sleeve gastrectomy for type 2 diabetes mellitus: a randomized controlled trial. Arch Surg. 2011;146(2):143–148. [17] Zhu L, Mo Z, Yang X, et al. Effect of laparoscopic Rouxen-Y Gastroenterostomy with BMI < 35 kg/m(2) in type 2 diabetes mellitus. Obes Surg. 2012;22(10):1562–1567. [18] Karra E, Yousseif A, Batterham RL. Mechanisms facilitating weight loss and resolution of type 2 diabetes following bariatric surgery. Trends Endocrinol Metab. 2010;21(6):337–344. [19] Mingrone G, Castagneto-Gissey L. Mechanisms of early improvement/resolution of type 2 diabetes after bariatric surgery. Diabetes Metab. 2009;35(6 Pt 2):518–523. [20] Patriti A, Aisa MC, Annetti C, et al. How the hindgut can cure type 2 diabetes. Ileal transposition improves glucose metabolism and beta-cell function in Goto-kakizaki rats through an enhanced Proglucagon gene expression and Lcell number. Surgery. 2007;142(1):74–85. [21] Rubino F, R’Bibo S L, del Genio F, et al. Metabolic surgery: the role of the gastrointestinal tract in diabetes mellitus. Nat Rev Endocrinol. 2010;6(2):102–109. [22] Rubino F, Gagner M. Potential of surgery for curing type 2 diabetes mellitus. Ann Surg. 2002;236(5):554–559. [23] Mingrone G, DeGaetano A, Greco AV, et al. Reversibility of insulin resistance in obese diabetic patients: role of plasma lipids. Diabetologia. 1997;40(5):599–605. [24] Peterli R, Wolnerhanssen B, Peters T, et al. Improvement in glucose metabolism after bariatric surgery: comparison of laparoscopic Roux-en-Y gastric bypass and laparoscopic sleeve gastrectomy: a prospective randomized trial. Ann Surg. 2009;250(2):234–241. [25] Patel RT, Shukla AP, Ahn SM, et al. Surgical control of obesity and diabetes: the role of intestinal vs. gastric mechanisms in the regulation of body weight and glucose homeostasis. Obesity (Silver Spring). 2014;22(1):159–169. [26] Troy S, Soty M, Ribeiro L, et al. Intestinal gluconeogenesis is a key factor for early metabolic changes after gastric bypass but not after gastric lap-band in mice. Cell Metab. 2008;8(3):201–211. [27] Phillips RJ, Walls EK, Powley TL. Duodenogastric reflux of intestinal infusions in rats is volume dependent. Appetite. 1996;27(1):79–90. [28] Stearns AT, Balakrishnan A, Rhoads DB, et al. Diurnal expression of the rat intestinal sodium-glucose cotransporter 1 (SGLT1) is independent of local luminal factors. Surgery. 2009;145(3):294–302.
Copyright of Journal of Investigative Surgery is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
