beta-Adrenergic receptors in aged rat brain: reduced number and capacity of pineal gland to develop supersensitivity.

The density but not the affinity of beta-adrenergic receptors declined significantly with age in rat pineal gland, corpus striatum, and cerebellum, as determined by the binding of tritiated dihydroalprenolol. Exposing rats to light for 12 hours increased the binding of this radioligand in 3-month-old but not in 24-month-old rats. The reduced responsiveness to catecholamines seen in aging may be due to a decrease in the number of beta-adrenergic receptors which, in turn, may be caused by an impaired capacity of receptors in aged animals to adapt to changes in adrenergic neuronal input.