Localization of glycogen synthase activity in liver of fasted normal and adrenalectomized rats after injection of dexamethasone

Abstract

Hepatic glycogen synthase activity was localized in normal and adrenalectomized (ADX) rats after fasting overnight and in fasted ADX rats after injection of dexamethasone (DEX) 2-8 h prior to sacrifice to stimulate glycogen synthesis. Cryostat sections were incubated in medium containing substrate to demonstrate glycogen synthase activity as indicated by glycogen synthesized during incubation. Sections from fasted normal rats showed limited dispersed glycogen synthase activity in both periportal and centrilobular regions. In contrast, activity for glycogen synthase in hepatocytes from fasted ADX rats appeared as large aggregates in random hepatocytes throughout the lobule. Two hours after injection of DEX the reaction product appeared as aggregates in some hepatocytes, but other cells revealed dispersed enzyme activity. Glycogen synthase activity was evident in more hepatocytes after 4 h treatment with DEX and after 8 h virtually all hepatocytes contained abundant reaction product. The results suggest that synthase activity becomes concentrated in limited regions of selected hepatocytes in fasted ADX rats. DEX stimulation of glycogen synthesis for 4-8 h results in increased enzyme activity.