Age-related alterations of isoproterenol-stimulated adenylyl-cyclase activity are partially corrected by thymic graft.

Previous experimental results have demonstrated progressive impairments in beta-adrenergic responsiveness with advancing age. Beta-adrenoceptors are involved in the alterations as their density progressively decreases during aging. Alterations in both in vivo responsiveness and receptor density are corrected by neonatal thymic grafts. In the present paper adenylyl-cyclase (AC) activity has been studied in the same animal models used before. Results show that no statistically significant changes can be observed when AC is assayed in absence of beta-adrenergic stimulation. On the contrary, when assayed after Isoproterenol stimulation, AC activity shows a shift of the peak and a decrease of its height in aged animals. A neonatal thymus grafted into old recipients one month before the experiment was performed, is capable of correcting the altered height of the peak but not the peak concentration.