Insulin regulates liver glycogen synthase and glycogen
phosphorylase activity reciprocally in rhesus monkeys.
Ortmeyer, Heidi K., Noni L. Bodkin, and Barbara C. Hansen.
Obesity and Diabetes Research Center, Department of Physiology,
School of Medicine, University of Maryland at Baltimore, Baltimore,
MD 21201
APStracts 3:0210E, 1996.
In skeletal muscle of both humans and monkeys the effects of in vivo
insulin during a euglycemic hyperinsulinemic clamp on the enzymes and
substrates of glycogen metabolism have been well established. In
liver, such effects of insulin during a clamp have not been
previously studied in primates. In order to examine insulin action at
the liver, euglycemic hyperinsulinemic clamps were performed in 10
lean young adult male rhesus monkeys. Liver biopsies were obtained at
3 time points: basal (fasting) - immediately before the onset of the
clamp, and during insulin infusion at 130 min and 195 min. Glycogen
synthase (GS), glycogen phosphorylase (GP), glucose 6-phosphate (G6P)
and glycogen were determined at each time point, with the greatest
effects observed most frequently at 195 min. Whole-body insulin
-mediated glucose disposal rate was related to the change in the
independent activity of GS (r=0.63, p<0.05). Insulin increased
the GS fractional activity (p<0.005) and decreased the
activity ratio of GP (p<0.001) compared to basal. The changes
in fractional activity of GS and in activity ratio of GP were
inversely related (r=-0.68, p<0.05). G6P concentration was
decreased during insulin stimulation compared to basal (p=0.01).
Glycogen concentration was not significantly different between the
basal and insulin-stimulated time points. We conclude that insulin
during a euglycemic clamp activates liver GS while inhibiting liver
GP, and that insulin action on liver GS is positively related to
whole-body insulin-mediated glucose disposal rates in lean young
adult rhesus monkeys.
Received 18 March 1996; accepted in final form 3 August 1996.
APS Manuscript Number E138-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996