Beta adrenergic regulation of rat liver glycogenolysis during aging

Abstract

Studies from a number of laboratories demonstrate a biphasic change in beta adrenergic regulation of hepatic glycogenolysis over the life span of the male rat. The beta adrenergic response is prominent in immature animals, declines rapidly during subsequent development to a minimum by the time of young adulthood, and then reemerges during postmaturational development. Age changes in beta adrenergic-responsive adenylate cyclase activity follow a "U"-shaped curve similar to that described by changes in liver glycogenolytic responsiveness during aging. Developmental and postmaturational changes in beta adrenergic-sensitive adenylate cyclase activation are related to parallel alterations in the density of beta adrenergic receptors and also to functional changes in nonreceptor components of the enzyme. The prevailing view that catecholamines stimulate hepatic glycogenolysis by an alpha adrenergic receptor-mediated, cyclic AMP-independent mechanism is based almost entirely on evidence from young adult male rats. We propose that current concepts of alpha adrenergic-responsive liver glycogenolysis underestimate a physiological role for beta adrenergic responsiveness over the majority of the life span.