Effect of Adrenalectomy on the Diurnal Variation in Glycogen Metabolism in Starved-Refed Rats

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Abstract
The role of glucocorticoid (GC) in the diurnal variation of glycogenesis, glycogenolysis and hepatic glycogen levels was studied in starved-refed rats. Intact, adrenalectomized (ADX) and ADX-GC supplemented rats were either ad libitum fed a 65% glucose diet or starved for 48 hours and refed the glucose diet. At the end of the starvation period and at 4-hour intervals thereafter, rats from all six treatment groups were killed and hepatic glycogen levels, glycogen synthase and phosphorylase activity determined. Ad libitum-fed animals displayed the usual diurnal glycogen and enzyme activity rhythms. Adrenalectomy was without effect in the ad libitum-fed rats on glycogen level and glycogen synthase activity and, at most points, on phosphorylase activity. Starvation-refeeding profoundly affected both the synthesis and degradation of glycogen and these effects could, in part, be attributed to the presence or absence of the adrenals. The phosphorylase activity and the hepatic glycogen level appeared to be cued by GC, whereas GC was without effect on glycogen synthase. Starvation-refeeding stimulated glycogen synthase activity within the first 4 hours of refeeding in the intact rats and within the first 8 hours of refeeding in the ADX-GC rats. These results suggest that the glycogen response to starvation refeeding is, in part, mediated by the adrenal hormones.