Effect of immobilization stress on rat pineal beta-adrenergic receptor-mediated function.

The results of this investigation indicate that stress produced by immobilization alters rat pineal function. Chronic stress reduced the density of pineal beta-adrenergic receptors and the activities of the intracellular enzyme serotonin N-acetyltransferase (NAT), its product N-acetylserotonin (NAS), and the pineal hormone melatonin, which was measured during the dark phase of the diurnal lighting cycle. Removal of the adrenal medulla did not prevent the reduction of pineal beta-adrenergic receptor binding sites that is observed after chronic stress. Acute immobilization stress suppressed the dark-induced elevations of pineal NAT activity and NAS levels 10 h after the stress session without altering pineal beta-adrenergic receptor binding. Although the precise mechanisms responsible for these effects are not completely clear, the results indicate that they are related to changes in sympathetic neuronal activity and not mediated by stress-induced elevations in plasma catecholamines.