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CAN. J . PHYSIOL. PHARMPICOP,. VOL. 53. 1975
The Effect of Somatostatin on Release and Insulinotropic Action of Gastric Inhibitory Polypeptide RAYMONDA. PEDERSON,~ JILL W. DRYBURGH, A N D JOHN C. BROWN Department ofPhysiolugy, CJniversiryof British Codumbia, Vrarzc-c~rlver, British Columbiu V6T l W.5 Received Febn~ary3, 1975
PEDERSON, R. A., DRYBURGH, 9. R..and BROWN,J. C. 1945. The effect of somatostatin on release and insulinotropic action of gastric inhibitory polypeptide. Can. J. Physid. Pharmacol. 53, 1200- 1205. Studies were carried out in conscious dogs in which the effect of intravenous somatostatin on immunoreactive gastric inhibitory polypeptide (IR-GIP) release was investigated. In addition. the inhibitory action of somatostatin on the insulin response to pure porcine GIP was assessed. Intravenous administration of somatostatin resulted in a delayed HR-GHP and immunoreactive insulin (BRI) response to oral glucose. Somatostatin also delayed the IR-GIP response to the ingestion of fat' In both types of experiments, initial depression of IRI levels was followed by a sharp rise in IRI release. Hntravenoaas infusion of somatostatin produced 80% inhibition of the IRI response to pure porcine GIP. It was sonclaaded that somatostatin inhibits the physiological release of IR-GIP and the insulinotropic action of exogenoils porcine GIP.
Introduction The polypeptide, growth hormone release inhibitory factor (GH-RIF) or somatostatin, has bccn shown to be a potent inhibitor of growtl~hormone release (Hall et ak. 1973). This polypeptide has also been demonstrated to block both insulin and glucagon release in the fasting state and after glucose loading in man (Alberti et ak. 1973: Mortimer et al. 1974; Koerkcr el wk. 1974). Gastric inhibitory polypeptide (GIP), a potent inhibitor of gastric acid secretion (Pederson and Brown 1972 1, has recently been shown to potentiate the insulin response to an intravenous glucose load in man (Bupre et al. 2973) and thc dog (Pederson et al. 1975a) and to release insulin under fasting conditions in the dog (Pederson et al. 1 9 7 b ) . These findings, when taken witla the evidence that oral glucose is a potent stimulant for immunoreactive GIP release (Cataland et al. 1973), suggest participation of GTP in the hormonal mechanism responsible for the potcntiation of insulin release observed after oral administration of glucose. The association between GIP and ii~sulinrelease provided the rationale for 'Address request for reprints to: Department of Physiology, University sf British Columbia, Vancouver, B.C. V6T 1W5. 'Abbreviations: IR-GIP, immunoreactive gastric inhibitory polypeptide; IRI, hmunoreactive insulin; GM-RIF, growth hormone release inhibitory factor; GIP, gastric inhibitory polypeptide.
investigating the effects of somatostatin on (a) IR-GIP release and ( b ) the insulinotropic action of pure porcine GIP-
Methods Five dogs, of either sex, weighing 25-30 kg, were used in this study. All experiments were performed in conscious dogs previously fasted for 18 h. Blood was collected via an indwelling catheter in the right or left cephalic vein. Serum was assayed for glucsse, BR12 and LR-GIP. GIercose was administered orally as a 20% solution in distilled water. The oral fat used was Lipomerl (Upjohn Co. Ltd.), a palatable emulsion containing 66 g of triglycerides per 100 ml. Solutions were administered from a glass syringe fitted to a catheter, the tip of which was held inside the cheek near the posterior molars. Liquid deposited here induced swallowing. Intravenous porcine GIP and synthetic somatostatin were administered in saline via an indwelling intravenous catheter connected to a Harvard infusion pump. Assays Serum glucose concentrations were determined in duplicate using a Beckman glucose analyzer. Serum IRL concentrations were determined in duplicate by the Amersham-Searle insulin kit (bovine insulin standard). Serum %W-C;IP concentrations were determined in duplicate by the radioimmunoassay technique of Kuzio et al. (1974) (porcine GIP standard). Anulysis of Data Results are expressed as means r+ standard errors. Statistical significance, where stated, was determined using the Student f test. Unless otherwise indicated, serum IRT, IR-GIP, and glucose values are expressed in terms of change from the mean IRP, LR-GIP, o r glucose concentrations measured in three fasting serum samples, taken at 15-min intervals before the
COMMUNICATIONS a.
t Oral Glucose
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEW MEXICO on 11/22/14 For personal use only.
I Oral Glucose
I.V. Sornafostatin
2 a
-
l
o
-
50
0
Time
. 100
IJO
(min)
FIG. 1 . The effect of intravenous incremental serum ( A ) IR-GIP, ( B ) of glucose per kilogram. 0-0,1.0 3 pg somatostatin per per kilogram
+
-
injection of 3.0 kg of somatostatin per kilogram on the IRI, and ( C ) glucose responses to the ingestion of 1.8 g g oral glucose per kilogram; - - 0 , 1.0 g oral glucose kilogram.
start of the experiment. The control period before the start of the experiment was defined as three 15-min periods in which variation in glucose concentration was less than 2%. This method of data presentation was employed because of the variability in fasting serum insulin, glucose, and GIP concentrations in different dogs.
Results and Discussion In nine experiments in five dogs somatostatin was given as a single, rapid, intravenous injection immediately before oral administration of glucose. In the same number of control experiments oral glucose alone was given. Figures I A, B, and C show that in experiments in which oral glucose was preceded by intravenous somatostatin, inhibition of fasting serum IR-CIP,VRI, and glucose levels occurred followed by a delayed rise in these parameters. The delay in initiation of all three responses
was 20 rnin, with the IRI response rebouimdirng to levels greater than thc maximum values observed in control experiments (Fig. 1B). All three parameters were reduced sig~nifica~mlly from controls at the 15 rnin interval (IR-CIP, p < 0.0025; IRP, p < 0.0005; and glucose, p < 0.0005). The initial decrease in serum glucose values following somatostatin injection (Fig. l C ) may be attributable to the inhibitory action of somatostatin on glucagon release (Mortimer et ul. 1974; Gerich et ale 1975). The possibility exists that the delayed rise in glucose concentration following oral glucose resulted from an effect of somatostatin on glucose absorption from the gut and that the delayed IR-GIP response was secondary to this decreased glucose uptake. In eight experiments in four dogs, the effect of a I-h infusion of somatostatin on IR-GIP, IRI, and glucose
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CAN. J . PHYSIOL. PHARMACOI,. VOL. 53, 1975
IOU 7
Oral Glucose
C.
in
Oml Glucose
i
I
100
50 Time
1
150
I
180
(min)
FIG.2. The effect of a I-h intravenotrs infusion of 6 ,ug of somatostatin per kilogram per hour on the incremental serum (A) IR-GHP, ( B ) IWI, and ( C ) glucose responses to a 1.0 g oral glucose per kilogram. 0-0,8.0 g oral glucose per kilogram; g - - a, 1.8 g oral glucose per kilogram 4- 6 pg somatostatin per kilogram per hour.
levels following an oral glucose load was investigated (Fig. 2 ) . Under these experimental corsditions, the HW-GIP response to oral glucose was suppressed until cessatiors sf the somatostatin infusion (time, 60 min). The fact that serum glucose concentrations had risen to the same level as control values (eight experiments in four dogs) at the 60-min interval ( p > 0.05) indicates that the inhibition of gllucose-stimulated IR-GIP release by somatostatin was not secondary to delayed glucose absorption, though it does not rule out the possibility that somatostatin inhibits glucose absorption. The delayed rise in glucose (Fig.
2G) and the inhibition of iiasulin release folIswed by a rebound phenomenon (Fig. 2B) are consistent with the findings of Mc~rtirner et a&. (1974) on the effects sf an infusiois of somatostatin sna these parameters following an oral glucose load in man. The effect of somatostatin on the IR-GIP response to fat (10 experiments in 5 dogs) was compared to the IR-GIP response to fat alone in an equal number of experiments, to determine if the inhibition of IR-GIP release observed in Figs. 1A and 2A was a gluoserelated phenomenon. Figure 3 demonstrates that when somatostatin was injected before
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COMMUNICATIONS
tin
T
T
T
L0 C,
a -1
0
FIG.3. The effect of intravenous injection of 3.0 pg of somatostatin per kilogram on the incremental serum ( A ) TR-GIP, ( B ) IRI, and ( C ) glucose responses to the ingestion of 100 rnl of Lipomul. 0-0,oral Lipomul; @ - - 9, oral Liponad 3 pg/kg somatostatin.
+
ingestion of Zipomul, mean incremental IK-GIP levels were suppressed during the entire course of the experiment (periods 30-75, p < 0.005). Figure 3B shows that serum IKI levels, unchanged from fasting levels during control experiments, were transiently inhibited by somatostatin ( p < 0.05 at the 15-min imterval). This inhibition was followed by an elevation of incremental IRI values to a mean of 19.6 ,~U/ml.The rebound phenomenon observed in Figs. I B and 3B is difficult to interprct on the basis of glucose data. In the case of Fig. 3, the secondary rise in insulin release is not preceded by elevated glucose levels nor followed by a significant depression of glucose values. The fact that somatostatin inhibited insulin release from the isolated perfused pancreas (Alberti et al. 1973) suggests that somatostatin
acts at least in part directly on pancreatic P cells. Since GIP has been shown to stimulate insulin release in the fastcd dog in the absence of elevated seruna glucose levels (Pederson et csl. 1975b), it was of interest to investigate whether somatostatin blocks this insulinotropic action. Figure 4 shows the results of experiments in which a 5-rnin infusion of porcine GIP was administered with or without pretreatment with somatostatin. Ten experiments of each type were performed in five dogs. The results (Fig. 4 8 ) show an 80% reduction in the peak insulin response to GIP, suggesting direct inhibition of the insulinotropic action of GIP at the level of the pancreatic P cell. Depression of serum glucose values following somatostatin was significantly less ( p < 0.01 at the 15-min interval) than in control experiments (Fig. 4B).
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CAN. d.
r
PHYSIOL. PHARMACOI,.
VOL. 53, 1975
Somatostatin
28
0
18
Time
15
2Q
25
//-I 45
(rnirs)
FIG.4. The effect of intravenous injection of 3,0 pg of somatostatin per kilogram on the change in ( A ) IRI and ( B ) glucose concentrations produced by a 5-min intravenous infusion sf 1.5 pg of GIP per kilogram. 0-0,1.5 pg of GIP per kilogram; @ - - @, 3.5 pg of GYP per kilogram 4- 3 pg of somatostatin per kilogram.
In summargl, somatostatin blocks IR-GIP released by the secretogogucs, fat and glucose. In addition, somatostatin inhibits the insulinotropic action of exogenous GIP. Insufficient data exist at present to causally relate the inhibition of IR-GIP release from the gut with inhibition of IRI relcase by the pancreas. It is possible that somatostatin nonspecifically blocks ( a ) all stimulants of insulin release at the level of the p cell and ( b ) gastrointestinal hormone release from the gut mucosa. The reported inhibition of gastrin release by somatostatin (Bloom ct al. 1974) lends some support to the latter possibility. The hormonal status of somatostatin and
its relationship to GIP and insulin under physiological conditions can be established only by the use of specific methods of assaying ble~odlevels of this peptide. This work was supported by research grants hl% 1972 (J. C . Brown) and MA 5590 (R. A. Pederson) from the Medical Research Council of Canada and grant No. 65-2516 (R. A. Pederson) from the Research Coordinating Committee, Faculty of Medicine, University of British Colunnbia. We are indebted to Dr. Ralph Hirschmann, Merck, Sharp and Dohme, for the generous gift of somatostatin prepared by the hferck peptide group. We also thank Professor Victor Mutt for the supply of starting material for the purification of GIP.
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEW MEXICO on 11/22/14 For personal use only.
COMMUNICATIONS
AEBERTH. K. G. M. M., CHRISTENSEN, S. E., IVERSEN. J., N. J., PRANGE SEYER-HANSEN. K., CHRISTENSEN, HANSEN,A., LUNDRAEK, K.,and O v s ~ o v ,H. 1973. Inhibition of insulin secretion by somatostatin. Lancet ii, 1299-1301. ALFORI).,F. P., BLOOM,S. R.. NABARRO, J. D. N., HALA, R., BESSEM,G. M . , COY,D. H., KASTIN.A. J., and SCHALEY, A. V. 1974. Glucagon control of fasting glucose in man. L;ancet i, 974-977. BI,OOM, S. R., MORTIMER,C. H., THORNER,M. O., BESSER,G. M., HAL,L, W.,GOILIEZ-PAN, A., ROY,V . M.. Russ~a.~ R., C. G., COY. D. W., KASTIN.A. J., and S C H A L I .A. ~ , V. 1974. Inhibition of gastrin and gastricacid secretion by growth-hormone release-inhibiting hormone. Lancet ii, 1106-1 109. CA'TALAND. S., CROCKEFT,S. E., BROWN,J . C., and MAZZATERRI, E. 1,. 1974. Immunoreactive gastric inhibitory polypeptide ievels following oral glucose ingestion. J. Clin. Endocrinol. Metab. 39, 1453-1460. DUPRE,J . . ROSS,S. A., WATSON,D., and BROWN.J . C. 1973. Stimulation of insulin secretion by gastric inhibitory polypeptide in man. J . Clin. Endocrinol. Metab. 37, 826-828. GERICH,J. E.. LOVINGER, R., and GRODSKY, M. 1975. Inhibition by somatostatin of glracagon and insulin release from the perfused rat pancreas in response tc? arginine, isoproterenol a i d theophylline: Evidence for a preferential effect on glucagon secretion. Endocrinology, 96,749-754. HALL,R., RESSER,G. M., SCHALLY, A. V.. COY,D. H.,
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EVERED, D., GOI.DIE,D. J., KASTIN,A. J., McIP'~TEILLY, A. J.. MOHTIMER,C. H. PHENEKOS, C., TUNBRIDGE, W. M. G., and WEIGPJTMAN, D. 1973. Action of growthhormone-release inhibitory hormone in healthy men and in acromegaly. L,ancet ii, 581-584. KOBRKER, D. J., RUCH,W., CHIDECKOE, E., PALMER, J., Go~DMAN,C. J., ENSINCK, J., and GALE,C. C. 1974. Somatostatin: hypothalamic inhibitor of the endocrine pancreas. Science, 184,482-484. Kuzlo, K., DRYBURGH, J . K., MALLOY,J . M., and BROWN,J. C. 1974. Radioimmunoassay for gastric inhibitory polypeptide. Gastroenterology, 66,357-364. MOR'TIMEM, C. H., TUNBRIDGE, W. M. G., CARK,n., YEOMANS.L., LIND,T., COY,D. H., BLOOM,S. R., KASTIN,A., MALLINSON, C. N . , BESSER, G. M . , SCHALLY, A. V . , and HALI.,R. 9 7 4 . Effects of growthhormone release-inhibiting hormone on circulating glucagon. insulin, and growth hormone in normal, diabetic, acromegalic, and hypo-pituitary patients. Lancet i , 697-701. PEDERSON, R. A., and BROWN,J. C. 1972. Inhibition of histamine-, pentagastrin- and insulin-stimulated canine gastric secretion by pure gastric inhibitory polypeptide. Gastroenterology, 62,393-400. PEDERSON, R. A., SCHUBER'T, H. E., and BROWN,J. C. 19750. The insuli~~otropic action of gastric inhibitory polypeptide. Can. J. Physiol. Pharmacol. 5 3 , 2 17-223. 197%. Gastric inhibitory polypeptide: Its physioIogica1 release and insulinotropic action in the dog. Diabetes (In press).
On the Specificity of Histamine Hz-ReceptorAntagonists in the Rat Cerebral Cortex J . W. PHHLLIS, G . K. K O S - ~ O P O U L OASN,D A . ODUTOLA~ Lleppartrnent ~PfPlzysi~logy, Colie7gr of‘Metiic- in^, Univer.sity c$Sa~katchewnn, Srtskntoon, Saskntchrwan S7N OW0 Received October 7,1975 P'HILI-IS. J . W., KOSTOPOUL.CIS, G. K.. and ODUTOI.A,A. 1975. On the specificity of histamine H,-receptor antagonists in the rat cerebral cortex. Can. 9. Physiol. Pharrnacol. 53, 1205-1209. The effects of iontophoretically applied histamine H,-receptor antagonists and their antagonism of various amines, acetylcholine (ACh), and adenosine 5'-monophosphate (5'-AMP) were stisdied on spontaneously active rat cerebral cortical neurons. Mstiamide selectively blocked the depressant actions of histamine. Burimamide, in amounts necessary for histamine antagonism, also antagonized the depressant effects of noradrenaline, doparnine, and 5-hydroxytryptamine. Neither antagonist affected 5'-AMP-induced depressions, but both reduced or blocked the excitatory actions of ACh. It is concluded that metiamide may be useful as a reliable antagonist of H, receptors on cerebral cortical neurons.
PHIILIS,J . W.,KOS~OPOULOS. G. K. et ODUTOL.A, A. 1975. On the specificity of histamine Hz-receptor antagonists in the rat cerebral cortex. Can. .I. Physiol. Pharmacol. 53, 1205-1209. On a CtudiC les effets des antagonistes de l'histamine H, appliques par iontophorese et leur antagonisme de plusieurs amines, de l'acetylcholine ( ACh) et de I'adenosirae 5'-monophosphate 'Present address: Department sf Physiology, University of Goteborg, Gstebsrg, Sweden.
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CAN. J . PHYSIOL. PHARMPICOP,. VOL. 53. 1975
The Effect of Somatostatin on Release and Insulinotropic Action of Gastric Inhibitory Polypeptide RAYMONDA. PEDERSON,~ JILL W. DRYBURGH, A N D JOHN C. BROWN Department ofPhysiolugy, CJniversiryof British Codumbia, Vrarzc-c~rlver, British Columbiu V6T l W.5 Received Febn~ary3, 1975
PEDERSON, R. A., DRYBURGH, 9. R..and BROWN,J. C. 1945. The effect of somatostatin on release and insulinotropic action of gastric inhibitory polypeptide. Can. J. Physid. Pharmacol. 53, 1200- 1205. Studies were carried out in conscious dogs in which the effect of intravenous somatostatin on immunoreactive gastric inhibitory polypeptide (IR-GIP) release was investigated. In addition. the inhibitory action of somatostatin on the insulin response to pure porcine GIP was assessed. Intravenous administration of somatostatin resulted in a delayed HR-GHP and immunoreactive insulin (BRI) response to oral glucose. Somatostatin also delayed the IR-GIP response to the ingestion of fat' In both types of experiments, initial depression of IRI levels was followed by a sharp rise in IRI release. Hntravenoaas infusion of somatostatin produced 80% inhibition of the IRI response to pure porcine GIP. It was sonclaaded that somatostatin inhibits the physiological release of IR-GIP and the insulinotropic action of exogenoils porcine GIP.
Introduction The polypeptide, growth hormone release inhibitory factor (GH-RIF) or somatostatin, has bccn shown to be a potent inhibitor of growtl~hormone release (Hall et ak. 1973). This polypeptide has also been demonstrated to block both insulin and glucagon release in the fasting state and after glucose loading in man (Alberti et ak. 1973: Mortimer et al. 1974; Koerkcr el wk. 1974). Gastric inhibitory polypeptide (GIP), a potent inhibitor of gastric acid secretion (Pederson and Brown 1972 1, has recently been shown to potentiate the insulin response to an intravenous glucose load in man (Bupre et al. 2973) and thc dog (Pederson et al. 1975a) and to release insulin under fasting conditions in the dog (Pederson et al. 1 9 7 b ) . These findings, when taken witla the evidence that oral glucose is a potent stimulant for immunoreactive GIP release (Cataland et al. 1973), suggest participation of GTP in the hormonal mechanism responsible for the potcntiation of insulin release observed after oral administration of glucose. The association between GIP and ii~sulinrelease provided the rationale for 'Address request for reprints to: Department of Physiology, University sf British Columbia, Vancouver, B.C. V6T 1W5. 'Abbreviations: IR-GIP, immunoreactive gastric inhibitory polypeptide; IRI, hmunoreactive insulin; GM-RIF, growth hormone release inhibitory factor; GIP, gastric inhibitory polypeptide.
investigating the effects of somatostatin on (a) IR-GIP release and ( b ) the insulinotropic action of pure porcine GIP-
Methods Five dogs, of either sex, weighing 25-30 kg, were used in this study. All experiments were performed in conscious dogs previously fasted for 18 h. Blood was collected via an indwelling catheter in the right or left cephalic vein. Serum was assayed for glucsse, BR12 and LR-GIP. GIercose was administered orally as a 20% solution in distilled water. The oral fat used was Lipomerl (Upjohn Co. Ltd.), a palatable emulsion containing 66 g of triglycerides per 100 ml. Solutions were administered from a glass syringe fitted to a catheter, the tip of which was held inside the cheek near the posterior molars. Liquid deposited here induced swallowing. Intravenous porcine GIP and synthetic somatostatin were administered in saline via an indwelling intravenous catheter connected to a Harvard infusion pump. Assays Serum glucose concentrations were determined in duplicate using a Beckman glucose analyzer. Serum IRL concentrations were determined in duplicate by the Amersham-Searle insulin kit (bovine insulin standard). Serum %W-C;IP concentrations were determined in duplicate by the radioimmunoassay technique of Kuzio et al. (1974) (porcine GIP standard). Anulysis of Data Results are expressed as means r+ standard errors. Statistical significance, where stated, was determined using the Student f test. Unless otherwise indicated, serum IRT, IR-GIP, and glucose values are expressed in terms of change from the mean IRP, LR-GIP, o r glucose concentrations measured in three fasting serum samples, taken at 15-min intervals before the
COMMUNICATIONS a.
t Oral Glucose
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEW MEXICO on 11/22/14 For personal use only.
I Oral Glucose
I.V. Sornafostatin
2 a
-
l
o
-
50
0
Time
. 100
IJO
(min)
FIG. 1 . The effect of intravenous incremental serum ( A ) IR-GIP, ( B ) of glucose per kilogram. 0-0,1.0 3 pg somatostatin per per kilogram
+
-
injection of 3.0 kg of somatostatin per kilogram on the IRI, and ( C ) glucose responses to the ingestion of 1.8 g g oral glucose per kilogram; - - 0 , 1.0 g oral glucose kilogram.
start of the experiment. The control period before the start of the experiment was defined as three 15-min periods in which variation in glucose concentration was less than 2%. This method of data presentation was employed because of the variability in fasting serum insulin, glucose, and GIP concentrations in different dogs.
Results and Discussion In nine experiments in five dogs somatostatin was given as a single, rapid, intravenous injection immediately before oral administration of glucose. In the same number of control experiments oral glucose alone was given. Figures I A, B, and C show that in experiments in which oral glucose was preceded by intravenous somatostatin, inhibition of fasting serum IR-CIP,VRI, and glucose levels occurred followed by a delayed rise in these parameters. The delay in initiation of all three responses
was 20 rnin, with the IRI response rebouimdirng to levels greater than thc maximum values observed in control experiments (Fig. 1B). All three parameters were reduced sig~nifica~mlly from controls at the 15 rnin interval (IR-CIP, p < 0.0025; IRP, p < 0.0005; and glucose, p < 0.0005). The initial decrease in serum glucose values following somatostatin injection (Fig. l C ) may be attributable to the inhibitory action of somatostatin on glucagon release (Mortimer et ul. 1974; Gerich et ale 1975). The possibility exists that the delayed rise in glucose concentration following oral glucose resulted from an effect of somatostatin on glucose absorption from the gut and that the delayed IR-GIP response was secondary to this decreased glucose uptake. In eight experiments in four dogs, the effect of a I-h infusion of somatostatin on IR-GIP, IRI, and glucose
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CAN. J . PHYSIOL. PHARMACOI,. VOL. 53, 1975
IOU 7
Oral Glucose
C.
in
Oml Glucose
i
I
100
50 Time
1
150
I
180
(min)
FIG.2. The effect of a I-h intravenotrs infusion of 6 ,ug of somatostatin per kilogram per hour on the incremental serum (A) IR-GHP, ( B ) IWI, and ( C ) glucose responses to a 1.0 g oral glucose per kilogram. 0-0,8.0 g oral glucose per kilogram; g - - a, 1.8 g oral glucose per kilogram 4- 6 pg somatostatin per kilogram per hour.
levels following an oral glucose load was investigated (Fig. 2 ) . Under these experimental corsditions, the HW-GIP response to oral glucose was suppressed until cessatiors sf the somatostatin infusion (time, 60 min). The fact that serum glucose concentrations had risen to the same level as control values (eight experiments in four dogs) at the 60-min interval ( p > 0.05) indicates that the inhibition of gllucose-stimulated IR-GIP release by somatostatin was not secondary to delayed glucose absorption, though it does not rule out the possibility that somatostatin inhibits glucose absorption. The delayed rise in glucose (Fig.
2G) and the inhibition of iiasulin release folIswed by a rebound phenomenon (Fig. 2B) are consistent with the findings of Mc~rtirner et a&. (1974) on the effects sf an infusiois of somatostatin sna these parameters following an oral glucose load in man. The effect of somatostatin on the IR-GIP response to fat (10 experiments in 5 dogs) was compared to the IR-GIP response to fat alone in an equal number of experiments, to determine if the inhibition of IR-GIP release observed in Figs. 1A and 2A was a gluoserelated phenomenon. Figure 3 demonstrates that when somatostatin was injected before
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEW MEXICO on 11/22/14 For personal use only.
COMMUNICATIONS
tin
T
T
T
L0 C,
a -1
0
FIG.3. The effect of intravenous injection of 3.0 pg of somatostatin per kilogram on the incremental serum ( A ) TR-GIP, ( B ) IRI, and ( C ) glucose responses to the ingestion of 100 rnl of Lipomul. 0-0,oral Lipomul; @ - - 9, oral Liponad 3 pg/kg somatostatin.
+
ingestion of Zipomul, mean incremental IK-GIP levels were suppressed during the entire course of the experiment (periods 30-75, p < 0.005). Figure 3B shows that serum IKI levels, unchanged from fasting levels during control experiments, were transiently inhibited by somatostatin ( p < 0.05 at the 15-min imterval). This inhibition was followed by an elevation of incremental IRI values to a mean of 19.6 ,~U/ml.The rebound phenomenon observed in Figs. I B and 3B is difficult to interprct on the basis of glucose data. In the case of Fig. 3, the secondary rise in insulin release is not preceded by elevated glucose levels nor followed by a significant depression of glucose values. The fact that somatostatin inhibited insulin release from the isolated perfused pancreas (Alberti et al. 1973) suggests that somatostatin
acts at least in part directly on pancreatic P cells. Since GIP has been shown to stimulate insulin release in the fastcd dog in the absence of elevated seruna glucose levels (Pederson et csl. 1975b), it was of interest to investigate whether somatostatin blocks this insulinotropic action. Figure 4 shows the results of experiments in which a 5-rnin infusion of porcine GIP was administered with or without pretreatment with somatostatin. Ten experiments of each type were performed in five dogs. The results (Fig. 4 8 ) show an 80% reduction in the peak insulin response to GIP, suggesting direct inhibition of the insulinotropic action of GIP at the level of the pancreatic P cell. Depression of serum glucose values following somatostatin was significantly less ( p < 0.01 at the 15-min interval) than in control experiments (Fig. 4B).
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEW MEXICO on 11/22/14 For personal use only.
CAN. d.
r
PHYSIOL. PHARMACOI,.
VOL. 53, 1975
Somatostatin
28
0
18
Time
15
2Q
25
//-I 45
(rnirs)
FIG.4. The effect of intravenous injection of 3,0 pg of somatostatin per kilogram on the change in ( A ) IRI and ( B ) glucose concentrations produced by a 5-min intravenous infusion sf 1.5 pg of GIP per kilogram. 0-0,1.5 pg of GIP per kilogram; @ - - @, 3.5 pg of GYP per kilogram 4- 3 pg of somatostatin per kilogram.
In summargl, somatostatin blocks IR-GIP released by the secretogogucs, fat and glucose. In addition, somatostatin inhibits the insulinotropic action of exogenous GIP. Insufficient data exist at present to causally relate the inhibition of IR-GIP release from the gut with inhibition of IRI relcase by the pancreas. It is possible that somatostatin nonspecifically blocks ( a ) all stimulants of insulin release at the level of the p cell and ( b ) gastrointestinal hormone release from the gut mucosa. The reported inhibition of gastrin release by somatostatin (Bloom ct al. 1974) lends some support to the latter possibility. The hormonal status of somatostatin and
its relationship to GIP and insulin under physiological conditions can be established only by the use of specific methods of assaying ble~odlevels of this peptide. This work was supported by research grants hl% 1972 (J. C . Brown) and MA 5590 (R. A. Pederson) from the Medical Research Council of Canada and grant No. 65-2516 (R. A. Pederson) from the Research Coordinating Committee, Faculty of Medicine, University of British Colunnbia. We are indebted to Dr. Ralph Hirschmann, Merck, Sharp and Dohme, for the generous gift of somatostatin prepared by the hferck peptide group. We also thank Professor Victor Mutt for the supply of starting material for the purification of GIP.
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AEBERTH. K. G. M. M., CHRISTENSEN, S. E., IVERSEN. J., N. J., PRANGE SEYER-HANSEN. K., CHRISTENSEN, HANSEN,A., LUNDRAEK, K.,and O v s ~ o v ,H. 1973. Inhibition of insulin secretion by somatostatin. Lancet ii, 1299-1301. ALFORI).,F. P., BLOOM,S. R.. NABARRO, J. D. N., HALA, R., BESSEM,G. M . , COY,D. H., KASTIN.A. J., and SCHALEY, A. V. 1974. Glucagon control of fasting glucose in man. L;ancet i, 974-977. BI,OOM, S. R., MORTIMER,C. H., THORNER,M. O., BESSER,G. M., HAL,L, W.,GOILIEZ-PAN, A., ROY,V . M.. Russ~a.~ R., C. G., COY. D. W., KASTIN.A. J., and S C H A L I .A. ~ , V. 1974. Inhibition of gastrin and gastricacid secretion by growth-hormone release-inhibiting hormone. Lancet ii, 1106-1 109. CA'TALAND. S., CROCKEFT,S. E., BROWN,J . C., and MAZZATERRI, E. 1,. 1974. Immunoreactive gastric inhibitory polypeptide ievels following oral glucose ingestion. J. Clin. Endocrinol. Metab. 39, 1453-1460. DUPRE,J . . ROSS,S. A., WATSON,D., and BROWN.J . C. 1973. Stimulation of insulin secretion by gastric inhibitory polypeptide in man. J . Clin. Endocrinol. Metab. 37, 826-828. GERICH,J. E.. LOVINGER, R., and GRODSKY, M. 1975. Inhibition by somatostatin of glracagon and insulin release from the perfused rat pancreas in response tc? arginine, isoproterenol a i d theophylline: Evidence for a preferential effect on glucagon secretion. Endocrinology, 96,749-754. HALL,R., RESSER,G. M., SCHALLY, A. V.. COY,D. H.,
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EVERED, D., GOI.DIE,D. J., KASTIN,A. J., McIP'~TEILLY, A. J.. MOHTIMER,C. H. PHENEKOS, C., TUNBRIDGE, W. M. G., and WEIGPJTMAN, D. 1973. Action of growthhormone-release inhibitory hormone in healthy men and in acromegaly. L,ancet ii, 581-584. KOBRKER, D. J., RUCH,W., CHIDECKOE, E., PALMER, J., Go~DMAN,C. J., ENSINCK, J., and GALE,C. C. 1974. Somatostatin: hypothalamic inhibitor of the endocrine pancreas. Science, 184,482-484. Kuzlo, K., DRYBURGH, J . K., MALLOY,J . M., and BROWN,J. C. 1974. Radioimmunoassay for gastric inhibitory polypeptide. Gastroenterology, 66,357-364. MOR'TIMEM, C. H., TUNBRIDGE, W. M. G., CARK,n., YEOMANS.L., LIND,T., COY,D. H., BLOOM,S. R., KASTIN,A., MALLINSON, C. N . , BESSER, G. M . , SCHALLY, A. V . , and HALI.,R. 9 7 4 . Effects of growthhormone release-inhibiting hormone on circulating glucagon. insulin, and growth hormone in normal, diabetic, acromegalic, and hypo-pituitary patients. Lancet i , 697-701. PEDERSON, R. A., and BROWN,J. C. 1972. Inhibition of histamine-, pentagastrin- and insulin-stimulated canine gastric secretion by pure gastric inhibitory polypeptide. Gastroenterology, 62,393-400. PEDERSON, R. A., SCHUBER'T, H. E., and BROWN,J. C. 19750. The insuli~~otropic action of gastric inhibitory polypeptide. Can. J. Physiol. Pharmacol. 5 3 , 2 17-223. 197%. Gastric inhibitory polypeptide: Its physioIogica1 release and insulinotropic action in the dog. Diabetes (In press).
On the Specificity of Histamine Hz-ReceptorAntagonists in the Rat Cerebral Cortex J . W. PHHLLIS, G . K. K O S - ~ O P O U L OASN,D A . ODUTOLA~ Lleppartrnent ~PfPlzysi~logy, Colie7gr of‘Metiic- in^, Univer.sity c$Sa~katchewnn, Srtskntoon, Saskntchrwan S7N OW0 Received October 7,1975 P'HILI-IS. J . W., KOSTOPOUL.CIS, G. K.. and ODUTOI.A,A. 1975. On the specificity of histamine H,-receptor antagonists in the rat cerebral cortex. Can. 9. Physiol. Pharrnacol. 53, 1205-1209. The effects of iontophoretically applied histamine H,-receptor antagonists and their antagonism of various amines, acetylcholine (ACh), and adenosine 5'-monophosphate (5'-AMP) were stisdied on spontaneously active rat cerebral cortical neurons. Mstiamide selectively blocked the depressant actions of histamine. Burimamide, in amounts necessary for histamine antagonism, also antagonized the depressant effects of noradrenaline, doparnine, and 5-hydroxytryptamine. Neither antagonist affected 5'-AMP-induced depressions, but both reduced or blocked the excitatory actions of ACh. It is concluded that metiamide may be useful as a reliable antagonist of H, receptors on cerebral cortical neurons.
PHIILIS,J . W.,KOS~OPOULOS. G. K. et ODUTOL.A, A. 1975. On the specificity of histamine Hz-receptor antagonists in the rat cerebral cortex. Can. .I. Physiol. Pharmacol. 53, 1205-1209. On a CtudiC les effets des antagonistes de l'histamine H, appliques par iontophorese et leur antagonisme de plusieurs amines, de l'acetylcholine ( ACh) et de I'adenosirae 5'-monophosphate 'Present address: Department sf Physiology, University of Goteborg, Gstebsrg, Sweden.
