title: Age-related reduction of beta-adrenoceptor sensitivity in rat heart occurs by multiple mechanisms.
abstract: Myocardial responsiveness to catecholamines was evaluated by measuring isoproterenol-stimulated adenylate cyclase activities in myocardial particulate fractions from Fischer 344 rats of 3, 12, and 24 months of age. Dose-response curves of isoproterenol revealed a progressive increase in the activation constant (Kact) with advancing age. In addition, the maximal velocity (Vmax) for 12- and 24-month-old groups was about 20-25% lower than for the 3-month-old group. Analysis of receptor-binding data and nonreceptor-mediated enzyme activities suggests that the age-related decrease in Vmax for isoproterenol may result from a loss of myocardial beta-receptors, whereas the increase in Kact is probably due to a deficit in the postreceptor components of the receptor-cyclase complex.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000375:Aging; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D004082:Dihydroalprenolol / Q000378:metabolism; D006321:Heart / Q000187:drug effects / Q000254:growth & development*; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
chemical_list: D011943:Receptors, Adrenergic, beta; D004082:Dihydroalprenolol; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D007545:Isoproterenol