Glycogen metabolism and cyclic AMP levels in isolated islets of lean and genetically obese mice.

The levels of glycogen and cyclic AMP, incorporation of glucose into glycogen and activities of glycogen synthetase and phosphorylase were determined in pancreatic islets isolated from genetically obese mice and their lean litter-mates. Islets from obese mice had elevated glycogen levels, increased phosphorylase activity and an increased amount of glycogen synthetase in the physiologically more effective I-form, indicating an increased turnover of glycogen. There was no significant difference in cyclic AMP levels between islets of lean and obese mice, but inhibition of phosphodiesterase or stimulation of adenyl cyclase increased cyclic AMP levels more in obese than in lean mouse islets, indicating a more rapid turnover of cyclic AMP in the former. It is suggested that cyclic AMP stimulated phosphorolytic breakdown of glycogen may be one of the mechanisms responsible for the increased insulin secretory response to glucose observed in islets from genetically obese mice.