The Effect of Catecholamines and Fasting on Cyclic-AMP and Release of Glycerol from Human Adipose Tissue

Abstract

The effects of catecholamines and fasting on levels of cyclic AMP and release of glycerol from human adipose tissue have been studied. Isoprenaline (10-5 M) produced a prompt rise and fall in levels of cyclic-AMP associated with release of glycerol and fatty acids into the medium. Noradrenaline (10-4 M) had a similar effect which was potentiated by phentolamine (an α-adrenergic blocker). Insulin (10-8 M) reduced tissue levels of cyclic-AMP and release of glycerol that had been stimulated by isoprenaline (10-7 M). However, at higher doses of insulin (10-7 M) the reverse tendency was noted. Prostaglandins E1, E2 and A2 likewise inhibited the release of glycerol and reduced tissue levels of cyclic-AMP, whereas prostaglandins A1 and F2α were without effect. However, a period of fast (10 days) activated lipolysis as judged by an increase in basal release of glycerol without altering tissue levels of cyclic-AMP. Furthermore, at the end of the fast, isoprenaline still stimulated release of glycerol and increments in cyclic-AMP to a similar extent as before fasting. This suggests that lipolysis produced by fasting may not be dependent on stimulation of triglyceride-lipase by cyclic-AMP, since the lipase is still in an activatable state at the end of a fast.