Effects of compound 48/80 on hepatic glycogen and glucose-6-phosphatase early in the diurnal cycle of the rat.

The amount and distribution of glycogen as well as the activity of glucose-6-phosphatase (G-6-Pase) in the livers of rats were analyzed by biochemical and/or histochemical techniques. During the first 5 hr of the light cycle, livers of rats were sampled prior to and 30 min following an injection of compound 48/80 or Ringer's solution. Glycogen decreased significantly in response to sampling; however, treatment with compound 48/80 provoked an additional significant decrease in hepatic glycogen. These differences occurred irrespective of the time during the 5 hr that this was studied. The livers of the majority of the rats treated with compound 48/80 displayed a periportal distribution of glycogen, while those treated with Ringer's showed a more uniform pattern. Hepatic G-6-Pase activity was unchanged in either the Ringer's or compound 48/80 treated rats. These results indicated that (1) the significant glycogenolytic response occurs independently of the amount of glycogen present, (2) G-6-Pase activity is not affected within 30 min following the stimulation of glycogenolysis, (3) variation in glycogen patterns during depletion depends on the nature of the stimulus and/or degree of response, and (4) the amount of glycogen available for release is limited.