AJP - Endocrinology and Metabolism, Vol 258, Issue 1 E109-E116, Copyright © 1990 by American Physiological Society
Mechanisms underlying enhanced glycogenolysis in livers of 3,5,3'-triiodothyronine-treated rats
S. Nebioglu, P. Wathanaronchai, D. Nebioglu, E. L. Pruden and D. M. Gibson
Department of Biochemistry, School of Pharmacy, University of Ankara, Tandogan-Ankara, Turkey.
Rats trained on a diurnal controlled meal-feeding schedule and injected
with a single dose of 3,5,3'-triiodothyronine (T3) failed to accumulate
liver glycogen and incorporated less D-[6-3H]glucose into glycogen than
normally observed during the feeding period. In the experimental group, the
concentration of liver adenosine 3',5'-cyclic monophosphate (cAMP) did not
fall during feeding and the pattern of activities of glycogen
phosphorylase, glycogen synthase, and phosphorylase kinase remained
conductive to glycogenolysis. Liver lysosomal alpha-glucosidase activity
normally fell during feeding periods. After T3 treatment the activities of
alpha-glucosidase and two lysosomal cathepsins (B1 and D) were elevated.
The evidence suggests that T3 may induce both liver phosphorylase kinase
and lysosomal alpha-glucosidase. This outcome of T3 excess, in concert with
previously described T3-inducible systems, provides a plausible explanation
for the failure of glycogen accumulation in this experimental model.
