LOCALIZATION OF GLYCOGEN-SYNTHASE ACTIVITY IN LIVER OF FASTED NORMAL AND ADRENALECTOMIZED RATS AFTER INJECTION OF DEXAMETHASONE

Hepatic glycogen synthase activity was localized in normal and adrenal ectomized (ADX) rats after fasting overnight and in fasted ADX rats af ter injection of dexamethasone (DEX) 2-8 h prior to sacrifice to stimu late glycogen synthesis. Cryostat sections were incubated in medium co ntaining substrate to demonstrate glycogen synthase activity as indica ted by glycogen synthesized during incubation. Sections from fasted no rmal rats showed limited dispersed glycogen synthase activity in both periportal and centrilobular regions. In contrast, activity for glycog en synthase in hepatocytes from fasted ADX rats appeared as large aggr egates in random hepatocytes throughout the lobule. Two hours after in jection of DEX the reaction product appeared as aggregates in some hep atocytes, 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 r eaction product. The results suggest that synthase activity becomes co ncentrated in limited regions of selected hepatocytes in fasted ADX ra ts. DEX stimulation of glycogen synthesis for 4-8 h results in increas ed enzyme activity.