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Effect of Training and Detraining on In Vivo Insulin Sensitivity I. Nagasa wa' , Y. Sato2 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, Effect of Training and Detraining on in Vivo Insulin Sensitivity. mt j Sports Med, Vol 1 l,No 2, pp 107—110,1990.

Accepted after revision: July 4, 1989

Insulin sensitivity was determined in rats to clarify the effect of detraining at 1 (trained state), 2, 3, and 7 days (7 rats each) and 14 days (n = 8) after five weeks of voluntary training using euglycemic insulin clamp technique. The relationship between basal insulin and glucose shifted towards a decrease in metabolic insulin needs compared to

untrained controls (n = 20). During the insulin clamp study, to maintain comparable plasma glucose and insulin levels in all groups, the glucose infusion rate had to be increased significantly (p < 0.01) to 9.92 1.12 mg.kg' min compared to control group (6.57 0.57). This improved sensitivity persisted for 2 days after training but was significantly lowered in the 7-days-after group (p < 0.01). In summary, this study shows that training effect on insulin sensitivity can be determined after voluntary training in rat.

the insulin clamp technique after voluntary training, and to elucidate the changes in insulin sensitivity during the time following such training.

Materials and Methods

Housing and care of the animals: Male Wistar rats weighing from 280 to 300 g (9 weeks old) were kept with

free access to laboratory chow (CLEA CE-2, Japan) and water. They were placed in individual cages with a running wheel. For a 1-week stabilization period the door to the wheel part of the cage was kept closed. The temperature of the animal room was maintained at 23 °C and the lighting cycle was set from7:OOto l9:OOh. Experimental protocol: The rats were randomly assigned to five training groups. From 10 weeks of age, voluntary training using the running wheel (circumference 1.16 m; Shinano, Japan) was carried out for 5 weeks. Unless the rats ran at least 1000 m/day for 1 week, they were excluded from the training group. After 5 weeks the training was stopped by

Key words

closing the door again. Then, at 1, 2, 3, and 7 (n = 7 in each group) and 14 (n = 8) days after the last exercise day, insulin sensitivity was determined. Twenty control rats matching in weight to the training groups were chosen at the end of training, and were kept separately for 2 weeks or more without

Insulin sensitivity, training, detraining, rat,

having performed any physical training.

This training effect lasted 2 days after training.

glucose metabolism, insulin clamp technique

A number of studies have shown that physical training raises the in vivo insulin sensitivity (1, 14, 16, 17, 18, 19). LeBlancetal. (14) and Heathetal. (6) pointed outthat this effect of training persists only for a few days. Insulin sensitivity may be affected by variations in the affinity to the receptor, or

in the number of receptors (6, 10), and by participation of counter-regulatory hormones and metabolic activity of insulin after binding in the cell (6, 11, 17). Although physical training increases insulin sensitivity, the precise mechanisms of this improvement are not yet clear. Whether or not these effects persist during detraining, and to what degree they interfere with each other, remains obscure.

Int.J. Sports Med. 11(1990)107—110

GeorgThiemeVerlagStuttgart NewYork

Euglycemic insulin clamp study: Insulin sensitivity was assessed using hyperinsulinemic-euglycemic clamp (insulin clamp) technique (9, 10). After 20 h overnight fasting, an indwelling catheter (0.20 ID, 0.37 OD, Silastic, Dow Corning) was inserted into the femoral vein under pentobarbital an-

esthesia (40 mg kg' body wt IP) for intravenous infusion of exogenous glucose (10% solution wt . voV1) and insulin (4.4 mU . kg' . min1; Actrapid monocomponent, Novo, Denmark) by two syringe pumps (model STC-521, Terumo,

Japan) via a forked device. A second catheter was inserted into the jugular vein for blood sampling. The catheters were filled with saline containing heparin (10 U . mV 1) The insulin sensitivity was defined as the glucose infusion rate (GIR) expressed in milligrams per minute per kilogram of rat's weight during the 60 to 120 mm experimental periods. Basal glucose levels were maintained by determination of the blood glucose concentration every 5 mm, with periodic adjustment of a variable infusion of a glucose solution, as described previously (11). All studies were performed in a 25 °C air-conditioned room, and were started at 10:00 to 1l:OOh.

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Abstract

The purpose of this study was to quantitatively examine the elevation of insulin sensitivity in vivo in rats using

J. Nagasawa, Y. Saw and T. Ishiko

108 mt. J. Sports Med. 11(1990)

*

basal state and during euglycemic insulin clamp

400

Control

300

Training

2daysafter Training

3daysafter Training

100

(mg dl)

Basal

Clamp

68 2

68 2 66±4

17±2

67±2

7daysafter Training

l4daysafter

Insulin Basal

(1iU . mr1) Clamp

22 2

62 5

66±1

20±2

57±7

60 2*

60 2

15 3

54 5

63±2

63±3

17±2

61±5

65±2

65±1

18±2

65±4

66±3

ldayafter

n 1200

Glucose

53±3

Mean SEM Fig. 1 Body weight in each group at time of euglycemic insulin clamp study. There were no significant differences among the groups except the 14-days-after-training group which was significantly

* Significantly different from control and 2-days-after-training

groups, p