Time Course of In Vivo Insulin Sensitivity after a Single Bout of Exercise in Rats J. Nagasawa1, Y. Saw2, and T Ishiko1 'Chukyo University, School of Physical Education 2Research Center of Health, Physical Fitness and Sports, Nagoya University
J. Nagasawa, Y Sato and T Ishiko, Time Course of In Vivo Insulin Sensitivity after a Single Bout of Exercise in Rats. mt j Sports Mcd, Vol 12, No 4, pp 399— 402, 1991.
Accepted after revision: September 27, 1990
After a single bout of treadmill running (20 mmin — 1 hour), the time course of the in vivU insulin sen-
sitivity was determined in previously untrained rats. The glucose infusion rate (GIR, mg-kg • min 1) as an index of insulin sensitivity was assessed by the euglycemic insulin
clamp technique 1 (lh-post-Ex group), 3 (3h-post-Ex), 6 (6h-post-Ex) and 24 hours after exercise (24h-post-Ex), n = 8 in each group. GIRs increased with time from
5.72±1.02 (lh-post-Ex), to 7.58± 1.07 (3h-post-Ex), 10.31 1.52 (6h-post-Ex) and 10.23 1.62 (24h-post-Ex) vs control (5.51 0.63); the GIR in the 6h-post-Ex and the 24h-post-Ex were significantly higher than those in the con-
trol and the lh-post-Ex groups (p < 0.05). The rate of increase was equivalent to that observed after long-term training in our previous study. GIR of a-adrenergic blockade in-
fused 1 hour after exercise (lh-post-Exa) significantly increased (8.32 0.96) compared to the control and no exercise a-blocker-infused control (Ca) (p < 0.05). But no significant difference was shown between I h-post-Ex and 1 hpost-Exa groups. In the 3-blocker-infused group, GIR did not show a significant increase. These results indicate that an increase in the in vivo insulin sensitivity after a single bout
of exercise is not evident until 6 hours post-exercise. The delay in the sensitivity might partly be explained by the suppression caused by catecholamines via the a-mechanism.
In vivo insulin sensitivity rises significantly after long-term physical training (1, 9, 15), but this effect seems to be rapidly reduced by cessation of training in humans (1, 6, 9) and in rats (14). Therefore, it has been proposed that regular
bouts of exercise are important for maintaining high insulin sensitivity (6). This means that reiterating a singe! bout of exercise is necessary. To our knowledge, however, there has been no report which showed the detailed time course of in vivo insulin sensitivity after a single bout of exercise, and the mechanism on a variation of the insulin sensitivity after a single bout of exercise is still not clear.
Therefore, the present study was designed to reveal in detail the time course of in vivo insulin sensitivity after
a single bout of exercise. In addition, the effect of adrenergic blockades on the post-exercise insulin sensitivity was determined. Materials and Methods
Housing and care of animals Male Wistar rats aged from 9 to 12 weeks were used for the study. They were fed laboratory rat chow (CLEA CE-2, Japan) and water ad libitum. They were housed in individual cages for 1 week or more without performing any exercise before the study. The temperature and humidity of the animal room were set at 23 °C and at 55%, respectively, with a 12-hour light-dark cycle.
Euglycemic insulin clamp experiment Insulin sensitivity was defined as glucose infu-
sion rate (GIR, mgkg • min 1) assessed by the euglycemichyperinsulinemic clamp (insulin clamp) technique (10). Taking rapid metabolic variation after exercise into consid-
insulin sensitivity, exercise, rat, adrenergic blockade
eration, GIR was punctually determined during the last 30 mm
of the 90-mm experimental period. During the insulin clamp experiments, such data were cancelled if the coefficient of variation of steady-state blood glucose rose above 9 %. All experiments were performed in a 25 °C air-conditioned room.
Variation of insulin sensitivity after a single bout of exercise
mt. J. SportsMed. 12(1991)399—402
GeorgThieme Verlag StuttgartNewYork
The rats were randomly divided into a resting control (C) group (n = 8) and exercise groups. The exercise rats ran for the first time on a motor-driven treadmill (NATSUME KN-73, Japan) for 1 hour at 20 mmin To study the
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400 Int.J.SportsMed. 12 (1991) time course of insulin sensitivity after a single bout of exercise,
exercised rats were anesthetized by an intraperitoneal injection of pentobarbital sodium (40 mgkg 1 body weight) immediately after running, and then their femoral and jugular veins were connulated with catheters (Sailastic, Dow Corning, USA). The fasting glucose concentrations had been measured with blood collected from a tail vein about 1 week before the experiments. The insulin clamp experiments were started 1 hour after exercise for the I h-post-Ex group (n 8). Corresponding insulin clamp experiments were performed 3 hours (3h-post-Ex group, n = 8), 6 hours (6h-post-Ex group, n 8) and 24 hours (24h-post-Ex group, n = 8) after exercise. These
rats were anesthetized and cannulated about 60 minutes
before starting the insulin clamp experiments. These experiments were performed after 20 to 22 hours fast except for water, but 24h-post-Ex rats were subjected to 25 hours fast (1 h exercise + 24h fasting rest).
J. Nagasawa, Y. Saw, and T Ishiko
ance, and thereafter, Students's t-test for nonpaired samples was used. Probability level of less than 0.05 was regarded as statistically significant. Results
Characteristics of animals Body weight, blood glucose and plasma in-
sulin concentrations are listed in Table 1. Body weight of the 24h-post-Ex group rats averaged 304 I 4g, which was lower than that of the lh-post Exil and 6h-post-Ex groups (p < 0.05). Mean basal glucose concentration of the 3h-post-Ex group was significantly higher than that of all other groups except Ca
and lh-post-Exa groups (p