Influence of aging and thymus on the beta-adrenergic dependent adenylyl cyclase activity in mouse brain cortex

Beta-adrenoceptor (betaAR) density has previously been found altered in brain cortex of aging mice. In the present paper the question has been addressed whether adenylyl cyclase (AC) also presents similar age-related changes. Due to the fact that age-related receptor impairments have previously been corrected by thymic grafts, the influence of thymus was also studied. Therefore, experiments were performed on young, athymic nude young, old and thymus-grafted old mice. BetaAR characteristics and basal and isoproterenol-stimulated AC activity were assayed in the same membrane preparations. Our results confirm a decrease of receptor density of beta(1) subtype in both old and athymic nude young mice, paralleled by a decreased isoproterenol-stimulated AC activity. A neonatal thymus grafted into old recipients is able to correct the changes in receptor density and the height of the peak of AC response. The location of the peak, however, remains shifted to the right, as it occurs in nude and in untreated old mice. It can be concluded that alterations may occur at different steps along the stimulus transducing chain, as suggested by the differential effect induced by thymus on receptor changes, which are completely recovered, and AC activity alterations, only partially corrected.