AJP - Endocrinology and Metabolism, Vol 248, Issue 5 560-E566, Copyright © 1985 by American Physiological Society
cAMP-independent stimulation of glycogen phosphorylase in newborn rat hepatocytes
A. Noguchi, P. A. Jett and A. H. Gold
Postnatal development of glycogen phosphorylase activation by the
cAMP-independent pathway was examined in isolated rat hepatocytes from
control and propylthiouracil-treated congenital hypothyroid rat pups. At 5
days postnatum there was complete phosphorylase activation by
beta-adrenergic stimulation, glucagon, and the calcium ionophore A23187,
but no activation by alpha-adrenergic stimulation. Activation of
phosphorylase by angiotensin or vasopressin was less than in hepatocytes
from adult rats (P less than 0.01). At 28 days postnatum activation by all
of these hormones was complete. In the propylthiouracil-treated group
hormone responsiveness was similar to the control at 5 days postnatum.
However, alpha-adrenergic (P less than 0.025), angiotensin, and vasopressin
(P less than 0.05) activation was decreased at 28 days postnatum, and
beta-adrenergic, glucagon, and A23187 activation was complete. The
attenuated responses were restored by thyroxine replacement from 15 days
postnatum. [32P]Pi incorporation into phosphatidylinositol by epinephrine
and vasopressin in 28-day propylthiouracil-treated rats was lower than the
control (P less than 0.01). We speculate that the diminished phosphorylase
response of hepatocytes to alpha-adrenergic, vasopressin, or angiotensin
stimuli in the early neonatal period could be related to low receptor
numbers and the weaker phosphoinositide response during this period. Also,
the depressed phosphorylase response to alpha-adrenergic, vasopressin, and
angiotensin stimulation in congenital hypothyroidism at 28 days postnatum
could be related to a decrease in number of plasma membrane receptors for
these agonists.
