Je. Michaels et Rr. Cardell, LOCALIZATION OF GLYCOGEN-SYNTHASE ACTIVITY IN LIVER OF FASTED NORMAL AND ADRENALECTOMIZED RATS AFTER INJECTION OF DEXAMETHASONE, The Anatomical record, 236(3), 1993, pp. 486-492
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.