Glycogen metabolism in muscle. The circadian influence on the in vitro model.

Hemidiaphragms isolated from normal mice were incubated in a glucose-rich medium and the glycogen increments induced by this procedure were determined at 04(00), 08(00), 12(00), 16(00), 20(00) and 00(00) on different days. It was found that although the glycogen values were greater after the incubation than in the non-incubated hemidiaphragms, the increments were different according to the time-span studied. Thus, glycogen synthesis in muscle, even under in vitro conditions, undergoes circadian variation.