Adrenalectomy but not gonadectomy affects rat pineal β-adrenergic receptor density

Bilateral adrenalectomy, like chronic pineal denervation by means of superior cervical ganglionectomy, induced an increase in the morning levels of [¹²⁵I]iodopindolol (IPIN) binding to rat pineal membranes; this change may be related to the reduced input of catecholamines to the pinealocytes as suggested by the decrease in nocturnal pineal melatonin synthesis previously reported in adrenalectomized rats. Castrated rats did not show changes in IPIN binding to pineal membranes when measured either at middark or in chronically superior cervical ganglionectomized rats, suggesting that the regulation of pineal β-adrenergic receptors is independent from gonadal control.