Effect of aging on properties and function of beta-adrenoceptors in rat lung

beta-Adrenoceptor density and ligand affinity, basal adenylate cyclase activity and cAMP synthesis upon stimulation with forskolin, fluoride, guanine nucleotides (GTP or guanylyl imidodiphosphate (GppNHp) or isoproterenol in the presence of the nucleotides were studied in membranes prepared from lungs of young (aged 2-3 months) and of old (aged 24-25 months) male Wistar rats. There was a significant (P less than 0.05, 21%) increase in beta-receptor density and a significant (P less than 0.05, 38%) decrease in the percentage of high-affinity binding sites for isoproterenol. Both basal adenylate cyclase activity and that after stimulation with guanine nucleotides or isoproterenol in the presence of nucleotides were unaltered with age. Forskolin stimulation of cAMP synthesis was significantly reduced (by 24%, P less than 0.05) in tissues from older animals. It is suggested that the age-dependent changes in properties of beta-receptors in rat lungs are compensatory, in order to ensure equal cAMP production for equal agonist stimulation.