Adenylate cyclase in senescence: catecholamine and parathyroid hormone pathways.

There are significant changes in the adenylate cyclase complex of many tissues with age. These changes are not due to a single defect in the system. Rather, the defects may vary from tissue to tissue and may be multiple in nature. There are age-related changes described in the receptor, N-protein, and catalytic components of the adenylate cyclase receptor. Alteration of the level of the receptor may reflect increases in the circulating levels of the agonist with age. The mechanisms responsible for alterations in the N-protein and catalytic unit activity remain to be elucidated. Further work is also needed to determine if the age-related changes in cAMP production result in age-related changes in cAMP-dependent protein kinase activity and the phosphorylation of specific proteins. However, the age-related changes in adenylate cyclase activity that have already been described may at least partially explain the decreased responsiveness of some target tissues to hormones and drugs.