AJP - Endocrinology and Metabolism, Vol 272, Issue 1 E133-E138, Copyright © 1997 by American Physiological Society
Insulin regulates liver glycogen synthase and glycogen phosphorylase activity reciprocally in rhesus monkeys
H. K. Ortmeyer, N. L. Bodkin and B. C. Hansen
Department of Physiology, School of Medicine, University of Maryland at Baltimore 21201, USA.
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. 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 three time points: basal
(fasting), that is, immediately before the onset of the clamp, and during
insulin infusion at 130 and 195 min. Glycogen synthase (GS), glycogen
phosphorylase (GP), glucose 6-phosphate (G-6-P), 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 with basal. The
changes in fractional activity of GS and in activity ratio of GP were
inversely related (r = - 0.68, P < 0.05), G-6-P concentration was
decreased during insulin stimulation compared with 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.
