LOCALIZATION OF GLYCOGEN-PHOSPHORYLASE ACTIVITY IN LIVER OF FASTED NORMAL AND ADRENALECTOMIZED RATS AND IN FASTED ADRENALECTOMIZED RATS AFTER INJECTION OF DEXAMETHASONE
Je. Michaels et Rr. Cardell, LOCALIZATION OF GLYCOGEN-PHOSPHORYLASE ACTIVITY IN LIVER OF FASTED NORMAL AND ADRENALECTOMIZED RATS AND IN FASTED ADRENALECTOMIZED RATS AFTER INJECTION OF DEXAMETHASONE, The Anatomical record, 248(3), 1997, pp. 406-412
Background: The intralobular distribution of activity of glycogen phos
phorylase (GP), a key enzyme in the breakdown of glycogen, was evaluat
ed to determine changes during early glycogen synthesis, Hepatic GP ac
tivity was localized in normal and adrenalectomized (ADX) rats after f
asting overnight and in fasted ADX rats stimulated to synthesize glyco
gen by administration of dexamethasone (DEX) 2-8 h prior to sacrifice,
Methods: Cryostat sections were incubated in medium containing approp
riate substrate for demonstration of GP activity as indicated by glyco
gen synthesized by the enzyme during incubation. Results: In sections
from fasted normal rats, GP activity in hepatocytes varied from undete
ctable to substantial amounts with no notable periportal to pericentra
l gradient evident, In contrast, GP activity in sections from adrenale
ctomized fasted rats was concentrated in discrete aggregates in random
hepatocytes throughout lobules, Two hours after DEX injection, GP enz
yme activity occurred as single aggregates or in a dispersed pattern i
n many hepatocytes, By 4 h after DEX administration, most cells displa
yed GP enzyme activity, the concentration of which appeared to be grea
ter in pericentral cells than in periportal cells, Eight hours after i
njection of DEX, GP enzyme activity had increased and appeared more ev
enly distributed throughout the lobules, Conclusions: These results su
ggest that GP activity became concentrated in limited regions of selec
ted hepatocytes in fasted ADX rats, DEX stimulation of glycogen synthe
sis in these rats resulted in increased GP activity that was concentra
ted in pericentral cells after 4 h, After 8 h, activity increased and
was more evenly distributed throughout the lobules, The increase in GP
enzyme activity concurrent with overall glycogen synthesis suggests t
hat the enzyme may participate in glycogen turnover. (C) 1997 Wiley-Li
ss, Inc.