Glucocorticoids in metabolic control during exercise: glycogen metabolism.

In order to evaluate the participation of glucocorticoids in the control of glycogen metabolism during exercise, experiments were performed on male adrenalectomized and normal rats. In adrenalectomized rats swimming for 4 hours induced less pronounced increases in lactate concentrations in skeletal muscles than in normal rats (in FG fibers up to 10.7 +/- 1.0 vs 14.8 +/- 1.2 and in SO fibers up to 9.1 +/- 0.7 vs 12.5 +/- 0.7 mg x g-1 wet tissue). The glycogen drop in liver and oxidative muscles was also less pronounced (in liver by 14% vs 52%, in SO fibers by 33% vs 54% in normal rats). Swimming until exhaustion led to an extremely low glucose level in blood (1.89 +/- 0.12 mMol x L-1) in adrenalectomized rats. When they were treated with dexamethasone, the swimming duration was longer (12 +/- 1 hours vs 9 +/- 0.8 hours in saline treated), blood glucose level at exhaustion was higher (3.07 +/- 0.23 mMol x L-1) and the drop of hepatic and muscle glycogen was more pronounced. In normal rats hepatic glycogen content dropped by 68% after swimming for 4 hours. After swimming for 8 or 12 hours further decreases in hepatic glycogen content were insignificant. High levels of corticosterone in blood was found after swimming for 4 and 8 hours. After swimming for 16 hours corticosterone concentration was below normal and a new drop in liver glycogen (until a level constituting only 11% initial) was recorded. The results support the suggestion that glucocorticoids, regulate hepatic glycogen and peripheral glucose utilization during exercise, and also participate in the control of glycogenolysis in muscles.