Physiology&Behavior,Vol. 51, pp. 927-931, 1992
0031-9384/92 $5.00 + .00 Copyright© 1992PergamonPressLtd.
Printed in the USA.
Effects of Running Training on the Blood Glucose and Lactate in Rats During Rest and Swimming NOBUSUKE
T A N , *l K E I K O M O R I M O T O , * T A K A O S U G I U R A , * A K I O M O R I M O T O f AND NAOTOSHI MURAKAMIt
*Department of Biomechanics and Physiology, Faculty of Liberal Arts, Yamaguchi University, Yamaguchi City, Yamaguchi 753, Japan and 7-Department of Physiology, School of Medicine Yamaguchi University, Ube City, Yamaguchi 755, Japan Received 19 A u g u s t 1991 TAN, N., K. MORIMOTO, T. SUGIURA, A. MORIMOTO AND N. MURAKAMI. Effectsof running training on the blood glucoseand lactatein ratsduringrest and swimming. PHYSIOL BEHAV 51(5) 927-931, 1992.--The purpose of this study was to examine the effect of physical training on the concentrations of glucose and lactate in the blood of rats during rest and after an acute bout of exercise. We used the following types and periods of training; (i) swimming for 4 weeks, (ii) running for 4 weeks, and (iii) running for 10 weeks. The results clearly show that the resting levels of blood glucose was significantly lower in groups trained by either swimming or running than untrained groups. In addition, after the acute exercise of swimming, animals trained by either running or swimming showed a lower increase in the blood lactate than untrained animals. Furthermore, the increases in the blood glucose after swimming were significantly lower in the group trained by swimming for 4 weeks and by running for 10 weeks than in untrained groups. These results suggest that after physical training by running, animals show an adaptation in the changes in the blood glucose and the blood lactate that are induced by a different type of physical stress, swimming. Stress
Adaptation
Physical training
Exercise
Blood glucose
IT is well known that physical training induces organic and functional changes in the body. It is also generally believed that appropriate physical training brings about beneficial changes in the metabolic responses (1). Among them, the effect of exercise on the metabolism of glucose has been investigated by many researchers. Previous studies have clarified the mechanisms by which physical training enhances the insulin sensitivity to blood glucose in humans (15,20) and rats (2,13,16-19,22). However, since human subjects are not always homogeneous in such parameters as age, body weight and so on, it is still unclear whether physical training affects resting levels of blood glucose. Recent results using rats have suggested that resting levels of blood glucose decrease after physical training (25). However, other reports have shown that there are no significant differences in this parameter in trained and untrained rats (7,10,17-19,21-23,28). We speculated that these conflicting results might stem from variations in the experimental procedures (e.g., the intensity and duration of exercise or the method of blood sampling). The primary purpose of the present study is to investigate the effect of physical training on resting levels of blood glucose in rats. The blood samplings were performed through a chron-
Blood lactate
ically implanted catheter in conscious rats. All samples were drawn at about the same time while the rats were under thermoneutral conditions. To physically train the rats, we used the following types of exercise and periods of training: (i) swimming for 4 weeks, (ii) running for 4 weeks, and (iii) running for l0 weeks. The secondary purpose of this study was to examine whether rats trained by running also show adaptation in the changes in blood glucose and lactate induced by a different type of exercise, i.e. swimming. In previous studies, the effect of physical training was usually investigated by comparing the data obtained from various intensities or from different durations of training by the same exercise (3,5,10,21,28). However, it is difficult to obtain data from an appropriate untrained control group. For example, to obtain consistent data from rats running on a treadmill, the animals must first learn how to run on the machine. Therefore, it is difficult to interpret the data of the control animals who are neither adapted to nor trained for running on the treadmill. However, rats with or without training for running can easily swim. Also, in this study, swimming was used as the first experiment for the both groups of rats, so that the stress induced
Requests for reprints should be addressed to Nobusuke Tan, Yamaguchi University, Faculty of Liberal Arts, Department of Biomechanics and Physiology, Yamaguchi City, Yamaguchi 753, Japan.
927
928
I,\N, l:it ;~1
by swimming should be virtually the same tbr both groups. Therefore, we used this model to further examine the effects of physical training by running on changes in the blood glucose and lactate after the exercise of swimming.
IABIJ
5;1)[t ztctixil~ (~mol/g fnuscl¢? wet weight/ram)
METHOD
Six-week-old male albino rats (Wistar strain) with initial body weights of 160-180 g were used in this study. A total of 40 rats were randomly divided into five groups (8 rats per group). The animals were housed in individual plastic cages (4 rats in each cage) in a room maintained at 26 _+ 1°C, a temperature within the thermoneutral zone for rats, with 12:12 h light:dark cycle, with light on at 0700 h. Tap water and rodent chow were provided ad lib. In this study, we chose two different types and two different periods of training: (i) swimming for 4 weeks (4W-swimming, n = 8), (ii) running for 4 weeks (4W-running, n = 8), and (iii) running for 10 weeks (10W-running, n = 8). The remaining 16 rats were used for controls for 4 weeks (4W-control, n = 8) and 10 weeks (10W-control, n = 8). During the exercise of swimming, animals swam in a round pool (50 cm diameter). The water of the pool was circulated and its temperature was maintained at 36°C. The exercise of swimming was performed for 1 h per day, 5 days a week. During the exercise of running, animals ran on a treadmill. In the first week of training for running, rats ran for 1 h at the speed of 15 m/min. From the second week on, the rats ran for 1 h at the speed of 20 m/min. The rats ran for 1 h per day, 5 days a week. During the swimming and running, the trainer carefully watched each rat's condition, and when rats showed symptoms of fatigue, the exercise was stopped. One day after the end of training, the animals were catheterized with a cannula under general anesthesia (pentobarbital, 50 mg/kg, IP) for blood sampling. Polyvinyl tubing was inserted into the jugular vein, such that the tip of the tubing was located in the superior caval vein near the right atrium. The free end of the catheter was passed subcutaneously to the midscapular region, where it was brought through the skin behind the neck. The catheter was kept patent by daily flushes with heparinized 0.9% saline. Two days after implantation of the catheter (3 days after the end of training), we examined the blood glucose and lactate concentrations of the trained and control groups at rest and immediately after the end of swimming for 30 minutes. The volume of each blood sample was 0.1 ml. The experiments were carried out between 0930-1200 h. The blood glucose and the
[]
4W-oontrol (n=8)
[]
lOW-oontrol (n=8)
[]
4W-running (n=8)
[]
lOW-running(n=8)
•
4W-swimming (n=8) F N'S
400
I 3o0
"~ 200 0
100 0
1
i
( I | . \ N G t : S IN S [ I ( ( ' I N , X [ [ I)t:IISI)R()GINASt !SI)II) ~,('I'IVIIY IN PI.ANTARIS MIIS('L[ IN RESPONSI FO TRAINING BY R{INNING
lOweeks 4weeks FIG. 1. Mean total body weight (mean _+SEM).
4W-Control group 4W-Running group 10W-Control group 10W-Running group
5.(/I .5 .8~ 5.36 ¢~.80
! 0.4i ~ (L2S _+ ().5~; :+ 0 . 3 4 *
Values are mean :~ SEM. * p -~ 0.05 as compared with the respective control group. blood lactate were measured by a YSI glucose and lactate analyzer (model 2300STAT, Yellow Springs Instrument Co., Yellow Springs, OH). Two days after measurements of the blood glucose and lactate (5 days after the end of training), rats in 4W-control, 4W-running, 10W-control, and 10W-runninggroups were sacrificed with ether and plantaris muscle was rapidly removed and frozen in liquid nitrogen for later determination of succinate dehydrogenase (SDH) activity. Muscles were stored at - 8 5 ° C until analyzed. A portion of the muscle was homogenized using a glass homogenizer in ice-cold phosphate buffer (33.3 mM, pH 7.4) and the SDH activity was measured by the method ofCooperstein et al. (4). SDH activity was expressed in pmol/g muscle wet weight/ min. The data were analyzed statistically by student's t-test or by ANOVA. Differences were considered statistically significant when p < 0.05. RESULTS
Figure 1 shows the changes in mean body weight of the rats in the 4W-control (n = 8), 4W-running (n -- 8), 4W-swimming (n = 8), 10W-control (n = 8), and the 10W-running (n = 8) groups. There were no significant differences in the mean body weights between the training groups and the respective control groups. Table 1 shows the SDH activity in the plantaris muscle of rats from 4W-control, 4W-running, 10W-control, and 10Wrunning groups. The SDH activity in the 4W-running group was somewhat higher than those in the control group, although there was no statistical significance between these two groups. The SDH activity in the 10W-running was significantly higher than those in the control group. Figure 2 shows the blood levels of glucose (A) and lactate (B) in the rats from the 4W-control, 4W-running, and 4W-swimming groups during rest (30 min before the start of swimming), and after swimming for 30 min. As shown in Fig. 2(A), the resting levels of blood glucose in rats from either trained group were significantly lower than those of the control group. The blood glucose levels in rats from all groups significantlyincreased after swimming (p < 0.01). However the levels of blood glucose after swimming in the 4W-swimming group were still significantly lower than those of the 4W-control (p < 0.001) and 4Wrunning groups (p < 0.01). In Fig. 2(B), there were no significant differences in the resting levels of blood lactate among three groups. After swimming for 30 min, the blood lactate levels in the 4W-control and 4W-running groups significantly increased, but the increased levels of the blood lactate in the trained groups were significantly lower than those in the control group.
PHYSICAL TRAINING AND BLOOD GLUCOSE
A 120
[] []
4w-oontrol (n=8) 4W-running (n=8)
•
4W-swimming (n=8)
929
r-
p
0031-9384/92 $5.00 + .00 Copyright© 1992PergamonPressLtd.
Printed in the USA.
Effects of Running Training on the Blood Glucose and Lactate in Rats During Rest and Swimming NOBUSUKE
T A N , *l K E I K O M O R I M O T O , * T A K A O S U G I U R A , * A K I O M O R I M O T O f AND NAOTOSHI MURAKAMIt
*Department of Biomechanics and Physiology, Faculty of Liberal Arts, Yamaguchi University, Yamaguchi City, Yamaguchi 753, Japan and 7-Department of Physiology, School of Medicine Yamaguchi University, Ube City, Yamaguchi 755, Japan Received 19 A u g u s t 1991 TAN, N., K. MORIMOTO, T. SUGIURA, A. MORIMOTO AND N. MURAKAMI. Effectsof running training on the blood glucoseand lactatein ratsduringrest and swimming. PHYSIOL BEHAV 51(5) 927-931, 1992.--The purpose of this study was to examine the effect of physical training on the concentrations of glucose and lactate in the blood of rats during rest and after an acute bout of exercise. We used the following types and periods of training; (i) swimming for 4 weeks, (ii) running for 4 weeks, and (iii) running for 10 weeks. The results clearly show that the resting levels of blood glucose was significantly lower in groups trained by either swimming or running than untrained groups. In addition, after the acute exercise of swimming, animals trained by either running or swimming showed a lower increase in the blood lactate than untrained animals. Furthermore, the increases in the blood glucose after swimming were significantly lower in the group trained by swimming for 4 weeks and by running for 10 weeks than in untrained groups. These results suggest that after physical training by running, animals show an adaptation in the changes in the blood glucose and the blood lactate that are induced by a different type of physical stress, swimming. Stress
Adaptation
Physical training
Exercise
Blood glucose
IT is well known that physical training induces organic and functional changes in the body. It is also generally believed that appropriate physical training brings about beneficial changes in the metabolic responses (1). Among them, the effect of exercise on the metabolism of glucose has been investigated by many researchers. Previous studies have clarified the mechanisms by which physical training enhances the insulin sensitivity to blood glucose in humans (15,20) and rats (2,13,16-19,22). However, since human subjects are not always homogeneous in such parameters as age, body weight and so on, it is still unclear whether physical training affects resting levels of blood glucose. Recent results using rats have suggested that resting levels of blood glucose decrease after physical training (25). However, other reports have shown that there are no significant differences in this parameter in trained and untrained rats (7,10,17-19,21-23,28). We speculated that these conflicting results might stem from variations in the experimental procedures (e.g., the intensity and duration of exercise or the method of blood sampling). The primary purpose of the present study is to investigate the effect of physical training on resting levels of blood glucose in rats. The blood samplings were performed through a chron-
Blood lactate
ically implanted catheter in conscious rats. All samples were drawn at about the same time while the rats were under thermoneutral conditions. To physically train the rats, we used the following types of exercise and periods of training: (i) swimming for 4 weeks, (ii) running for 4 weeks, and (iii) running for l0 weeks. The secondary purpose of this study was to examine whether rats trained by running also show adaptation in the changes in blood glucose and lactate induced by a different type of exercise, i.e. swimming. In previous studies, the effect of physical training was usually investigated by comparing the data obtained from various intensities or from different durations of training by the same exercise (3,5,10,21,28). However, it is difficult to obtain data from an appropriate untrained control group. For example, to obtain consistent data from rats running on a treadmill, the animals must first learn how to run on the machine. Therefore, it is difficult to interpret the data of the control animals who are neither adapted to nor trained for running on the treadmill. However, rats with or without training for running can easily swim. Also, in this study, swimming was used as the first experiment for the both groups of rats, so that the stress induced
Requests for reprints should be addressed to Nobusuke Tan, Yamaguchi University, Faculty of Liberal Arts, Department of Biomechanics and Physiology, Yamaguchi City, Yamaguchi 753, Japan.
927
928
I,\N, l:it ;~1
by swimming should be virtually the same tbr both groups. Therefore, we used this model to further examine the effects of physical training by running on changes in the blood glucose and lactate after the exercise of swimming.
IABIJ
5;1)[t ztctixil~ (~mol/g fnuscl¢? wet weight/ram)
METHOD
Six-week-old male albino rats (Wistar strain) with initial body weights of 160-180 g were used in this study. A total of 40 rats were randomly divided into five groups (8 rats per group). The animals were housed in individual plastic cages (4 rats in each cage) in a room maintained at 26 _+ 1°C, a temperature within the thermoneutral zone for rats, with 12:12 h light:dark cycle, with light on at 0700 h. Tap water and rodent chow were provided ad lib. In this study, we chose two different types and two different periods of training: (i) swimming for 4 weeks (4W-swimming, n = 8), (ii) running for 4 weeks (4W-running, n = 8), and (iii) running for 10 weeks (10W-running, n = 8). The remaining 16 rats were used for controls for 4 weeks (4W-control, n = 8) and 10 weeks (10W-control, n = 8). During the exercise of swimming, animals swam in a round pool (50 cm diameter). The water of the pool was circulated and its temperature was maintained at 36°C. The exercise of swimming was performed for 1 h per day, 5 days a week. During the exercise of running, animals ran on a treadmill. In the first week of training for running, rats ran for 1 h at the speed of 15 m/min. From the second week on, the rats ran for 1 h at the speed of 20 m/min. The rats ran for 1 h per day, 5 days a week. During the swimming and running, the trainer carefully watched each rat's condition, and when rats showed symptoms of fatigue, the exercise was stopped. One day after the end of training, the animals were catheterized with a cannula under general anesthesia (pentobarbital, 50 mg/kg, IP) for blood sampling. Polyvinyl tubing was inserted into the jugular vein, such that the tip of the tubing was located in the superior caval vein near the right atrium. The free end of the catheter was passed subcutaneously to the midscapular region, where it was brought through the skin behind the neck. The catheter was kept patent by daily flushes with heparinized 0.9% saline. Two days after implantation of the catheter (3 days after the end of training), we examined the blood glucose and lactate concentrations of the trained and control groups at rest and immediately after the end of swimming for 30 minutes. The volume of each blood sample was 0.1 ml. The experiments were carried out between 0930-1200 h. The blood glucose and the
[]
4W-oontrol (n=8)
[]
lOW-oontrol (n=8)
[]
4W-running (n=8)
[]
lOW-running(n=8)
•
4W-swimming (n=8) F N'S
400
I 3o0
"~ 200 0
100 0
1
i
( I | . \ N G t : S IN S [ I ( ( ' I N , X [ [ I)t:IISI)R()GINASt !SI)II) ~,('I'IVIIY IN PI.ANTARIS MIIS('L[ IN RESPONSI FO TRAINING BY R{INNING
lOweeks 4weeks FIG. 1. Mean total body weight (mean _+SEM).
4W-Control group 4W-Running group 10W-Control group 10W-Running group
5.(/I .5 .8~ 5.36 ¢~.80
! 0.4i ~ (L2S _+ ().5~; :+ 0 . 3 4 *
Values are mean :~ SEM. * p -~ 0.05 as compared with the respective control group. blood lactate were measured by a YSI glucose and lactate analyzer (model 2300STAT, Yellow Springs Instrument Co., Yellow Springs, OH). Two days after measurements of the blood glucose and lactate (5 days after the end of training), rats in 4W-control, 4W-running, 10W-control, and 10W-runninggroups were sacrificed with ether and plantaris muscle was rapidly removed and frozen in liquid nitrogen for later determination of succinate dehydrogenase (SDH) activity. Muscles were stored at - 8 5 ° C until analyzed. A portion of the muscle was homogenized using a glass homogenizer in ice-cold phosphate buffer (33.3 mM, pH 7.4) and the SDH activity was measured by the method ofCooperstein et al. (4). SDH activity was expressed in pmol/g muscle wet weight/ min. The data were analyzed statistically by student's t-test or by ANOVA. Differences were considered statistically significant when p < 0.05. RESULTS
Figure 1 shows the changes in mean body weight of the rats in the 4W-control (n = 8), 4W-running (n -- 8), 4W-swimming (n = 8), 10W-control (n = 8), and the 10W-running (n = 8) groups. There were no significant differences in the mean body weights between the training groups and the respective control groups. Table 1 shows the SDH activity in the plantaris muscle of rats from 4W-control, 4W-running, 10W-control, and 10Wrunning groups. The SDH activity in the 4W-running group was somewhat higher than those in the control group, although there was no statistical significance between these two groups. The SDH activity in the 10W-running was significantly higher than those in the control group. Figure 2 shows the blood levels of glucose (A) and lactate (B) in the rats from the 4W-control, 4W-running, and 4W-swimming groups during rest (30 min before the start of swimming), and after swimming for 30 min. As shown in Fig. 2(A), the resting levels of blood glucose in rats from either trained group were significantly lower than those of the control group. The blood glucose levels in rats from all groups significantlyincreased after swimming (p < 0.01). However the levels of blood glucose after swimming in the 4W-swimming group were still significantly lower than those of the 4W-control (p < 0.001) and 4Wrunning groups (p < 0.01). In Fig. 2(B), there were no significant differences in the resting levels of blood lactate among three groups. After swimming for 30 min, the blood lactate levels in the 4W-control and 4W-running groups significantly increased, but the increased levels of the blood lactate in the trained groups were significantly lower than those in the control group.
PHYSICAL TRAINING AND BLOOD GLUCOSE
A 120
[] []
4w-oontrol (n=8) 4W-running (n=8)
•
4W-swimming (n=8)
929
r-
p
