AJP - Endocrinology and Metabolism, Vol 242, Issue 4 262-E272, Copyright © 1982 by American Physiological Society
Effect of vasoactive intestinal polypeptide on glycogen metabolism in rat hepatocytes
C. L. Wood and J. J. Blum
The effects of vasoactive intestinal polypeptide (VIP) on several enzymes
of glycogen metabolism in rat hepatocytes were compared with those of
glucagon and of vasopressin (ADH). VIP caused phosphorylase activation and
glycogenolysis in hepatocytes from fed rats. In hepatocytes from fasted
rats incubated with glucose, lactate, and pyruvate, VIP inhibited net
glycogen deposition, inactivated glycogen synthase, and activated
phosphorylase. VIP was about 100-fold less potent than glucagon and
1,000-fold less potent than ADH in causing activation of phosphorylase. The
ability of VIP to activate phosphorylase was not altered by chelation of
the calcium in the medium. The half maximal effective doses of VIP for both
phosphorylase activation and stimulation of glycogenolysis were 10-30 nM.
Treatment with VIP, ADH, or glucagon did not decrease phosphorylase
phosphatase activity. Each of these hormones, however, lengthened the lag
time before synthase phosphatase activity was expressed in vitro. Other gut
hormones tested did not affect hepatocyte glycogen metabolism. These
results do not support the concept of physiologic control of hepatic
glycogen metabolism by VIP or by other gut hormones.
