BETA-ADRENERGIC REGULATION OF RAT-LIVER GLYCOGENOLYSIS DURING AGING

Studies from a number of laboratories demonstrate a biphasic change in beta adrenergic regulation of hepatic glycogenolysis over the life sp an of the male rat. The beta adrenergic response is prominent in immat ure animals, declines rapidly during subsequent development to a minim um by the time of young adulthood, and then reemerges during postmatur ational development. Age changes in beta adrenergic-responsive adenyla te cyclase activity follow a ''U''-shaped curve similar to that descri bed by changes in liver glycogenolytic responsiveness during aging. De velopmental and postmaturational changes in beta adrenergic-sensitive adenylate cyclase activation are related to parallel alterations in th e density of beta adrenergic receptors and also to functional changes in nonreceptor components of the enzyme. The prevailing view that cate cholamines stimulate hepatic glycogenolysis by an alpha adrenergic rec eptor-mediated, cyclic AMP-independent mechanism is based almost entir ely on evidence from young adult male rats. We propose that current co ncepts of alpha adrenergic-responsive liver glycogenolysis underestima te a physiological role for beta adrenergic responsiveness over the ma jority of the life span.