Effect of Immobilization Stress on Rat Pineal β‐Adrenergic Receptor‐Mediated Function

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Abstract
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 [5-hydroxytryptamine] 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, they are related to changes in sympathetic neuronal activity and not mediated by stress-induced elevations in plasma catecholamines.