Glycogen content and glucose uptake in stimulated frog sartorius muscle: effects of prolonged incubation, insulin, and testosterone.

Abstract

Anin vitro preparation of electrically stimulated sartorius muscle of the frog was used as a model to investigate the effects of insulin and testosterone on the increased glycogen content of frog skeletal muscle that was observedin vivo 48 h after an exhaustive bout of treadmill exercise. Thein vitro preparation could effectively extract glucose from the bathing medium and continue glycogen synthesis for incubation periods up to 60 h, and the electrical stimulation depleted glycogen by 68%. Electrical stimulation enhanced rates of glucose uptake and glycogen synthesis when these variables were measured after prolonged periods of poststimulation incubation but did not cause an overshoot of glycogen storage similar to that observedin vivo. Stimulation did not produce increments in glycogen synthesis that were additive to those of insulin or testosterone. The absence of glycogen overshoot in thein vitro system may have resulted from the absence of neural factors.