Adrenergic beta-receptor activity and cyclic AMP metabolism in vascular smooth muscle; variations with age.

The relaxing effect of isoproterenol on aortic strips from rats decreases and disappears with increasing age of the animal. In aortas from young rats (1 month) the cAMP level increases after stimulation with isoproterenol (3.6 muM), whereas in old aortas (6 months) the cAMP level was unchanged. Basal and NaF stimulated adenyl cyclase activities are increased in aortas from rats 6 months of age compared with those one month old. The phosphodiesterase activities decrease with increasing age both low (10-7M) and high (10-4M) substrate concentration.