AJP - Endocrinology and Metabolism, Vol 243, Issue 6 464-E469, Copyright © 1982 by American Physiological Society
Influence of physical training on insulin release and glucose utilization by islet cells and liver glucokinase activity in the rat
W. Zawalich, S. Maturo and P. Felig
The effect of physical training on insulin release and glucose utilization
by perifused islets and on liver glucokinase activity was examined in rats
that exercised spontaneously by running (in wheel cage) up to 4-6 mi/day
for 36 +/- 4 days and in sedentary controls kept in standard cages.
Perifusion of islets with 4 mM glucose resulted in comparable rates of
insulin release from islets obtained from trained and sedentary control
rats. In contrast, when the perifusion glucose concentration was raised to
10 mM, the biphasic increase in insulin release was 40-50% lower in the
trained rats as compared with untrained rats. This decrease in
glucose-stimulated insulin release occurred in the face of comparable rates
of glucose utilization by islets from control and trained rats. Glucose
phosphorylation by liver homogenates from trained rats was reduced at all
concentrations of glucose examined (0.5-100 mM). The calculated glucokinase
activity was diminished by 40%, whereas hexokinase activity was decreased
by 15% in the livers from trained rats. We conclude that 1) hypoinsulinemia
induced by exercise training is due to decreased sensitivity of the
beta-cell to the stimulant action of glucose independent of changes in
islet cell utilization of glucose, and 2) exercise training results in a
diminution of liver glucokinase activity that may be a consequence of the
hypoinsulinemia.
