Cyclic AMP regulation of fuel metabolism during exercise: regulation of adipose tissue lipolysis during exercise.

Adipocytes from trained rats release more free fatty acids in response to hormonal challenge compared to fat cells from sedentary rats. Lipolysis results from increased triglyceride hydrolysis that is catalyzed by a hormone-sensitive lipase, which, in turn, is activated by a phosphorylation mechanism involving cyclic AMP-dependent protein kinase. Cyclic AMP levels within the fat cell are regulated by beta-adrenergic receptor/adenylate cyclase interactions and cyclic AMP phosphodiesterase activity. This review focuses on cyclic AMP regulation of lipolysis in adipocytes from trained and sedentary animals. Although lipolysis is elevated in fat cells from trained rats, no differences are found in beta-adrenergic receptor number or affinity, adenylate cyclase activity, protein kinase activity, or partially purified hormone-sensitive lipase activity when compared to sedentary rats. The major lipolytic alteration induced by exercise training appears to occur at a site distal to hormonal regulation of the beta-adrenergic receptor.