ON ROLE OF ADENYL CYCLASE IN REGULATION OF LIPOLYSIS IN FASTING

Epididymal fat pads from fasting rats were more sensitive to the lipolytic effects of theophylline than fat pads from fed animals, but the maximum response to this agent was the same in both groups. From these results it may be inferred that fasting did not change the amount of adipose tissue lipase. The amount of activatable adenyl cyclase in adipose tissue was increased about 2-fold by fasting, as shown by direct assay of the enzyme as well as by the increase in the maximum lipolytic response to norepinephrine (NE) in vitro. However, in vivo the adenyl cyclase appears to be activated by a nonadrenergic system, since the rise in free fatty acids (FFA) is not inhibited by propranolol, a beta adrenergic blocking drug, though it is inhibited by nicotinic acid. Kinetic analysis of the inhibitory effects of propranolol on lipolytic responses to NE in vitro suggest that characteristics of the receptor, presumably adenyl cyclase, are similar in fasting and fed animals. © 1969.