Exercise training prevents the maturation-induced decrease in
insulin sensitivity.
Nakai, Naoya, Yoshiharu Shimomura, Nobuko Ohsaki, Juichi Sato,
Yoshiharu Oshida, Isao Ohsawa, Noriaki Fujitsuka, and Yuzo Sato.
Research Center of Health, Physical Fitness and Sports, Nagoya
University, Chikusa-ku, Nagoya 464-01, Japan; and Department of
Bioscience, Nagoya Institute of Technology, Showa-ku, Nagoya 466,
Japan
APStracts 3:0070A, 1996.
We examined the effects of exercise training initiated prior to
maturation or after maturation on insulin sensitivity and GLUT-4
content in membrane fractions of skeletal muscle. Female Wistar rats
(4 wk of age) were divided into sedentary and exercise trained
groups. At 12 wk of age, a subset of the trained animals (TR) was
sacrificed along with a subset of sedentary controls (SED). Half of
the remaining sedentary animals remained sedentary (SED-SED) while
the other half began exercise training (SED-TR). The remaining rats
in the original trained group continued to train (TR-TR). Euglycemic
clamp (insulin infusion rate at 6 mU/kg body weight/min) was
performed at 4 wk, 12 wk, and 27 wk. Following euglycemic clamp in
all animals except 4 wk of age, hindlimb (gastrocnemius and part of
quadriceps) muscles were removed for preparation of membrane
fractions. In sedentary rats, glucose infusion rate (GIR) during
euglycemic clamp was decreased from 15.9 mg/kg/min at 4 wk of age to
9.8 at 12 wk of age and 9.1 at 27 wk of age. In exercise trained
rats, the GIR was not significantly decreased by maturation (at 12
wk) and further aging (at 27 wk). Initiation of exercise after
maturation restored the GIR at 27 wk of age to the same levels as
that for the corresponding exercise trained rats. GLUT-4 content in
plasma and intracellular membrane fractions of hindlimb muscle
obtained just after euglycemic clamp showed the same trend as the
results of GIR. These results suggest that exercise training
prevented the maturation-induced decrease in insulin sensitivity.
Improvement of insulin sensitivity caused by exercise training were
attributed at least in part to the increase in insulin-sensitive
GLUT-4 on the plasma membrane in skeletal muscle.
Received 6 July 1995; accepted in final form 17 January 1996.
APS Manuscript Number A726-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96