ABSTRACT
Many of the hormones interacting with membrane receptors exert their effects at least partially through the activation of "adenylate cyclase." Certain hormones which attach to cell membrane receptors do not appear to activate adenylate cyclase. Diploid fibroblasts have been employed to compare age-related changes in insulin responsiveness to changes in insulin-receptor concentrations. Since hormone binding to receptors is the initial and in many cases a regulatory step in hormone actions, receptor changes during aging have been studied extensively. As with steroid receptors, despite a few possibly controversial cases, a great number of membrane hormone receptors are lost during aging. V. K. Moudgil and M. S. Kanungo reported a progressive decrease with age in the ability of estradiol to induce the enzyme acetylcholinesterase in rat brain in vivo. Changes in certain hormone-receptor concentrations may provide explanations for many cases of altered responsiveness to hormones during aging.
