Modulation of beta-adrenergic receptors in the pituitary gland following adrenalectomy in rats

Beta-adrenergic receptor subtypes in human pineal gland

The secretion of melatonin by the pineal has been promoted as a direct monitor of adrenergic function in depressive illness. However, discrepant findings have been reported, possibly reflecting a complex adrenergic regulation of pineal output. In order to clarify the anatomical localization and relative density of beta-adrenergic receptors and their subtypes in human pineal, quantitative autoradiographic analysis was conducted of beta-adrenergic receptors in postmortem specimens using the high affinity radioligand 125I-pindolol. Dense specific binding was found throughout the gland. beta 1 -adrenergic receptors were more numerous, but beta 2-receptors were present in an overlapping anatomical distribution with beta 1-receptors.

Cyclic AMP-dependent modulation of interleukin-1 receptors in the mouse AtT-20 pituitary tumor cell line

Previous studies have demonstrated an upregulation of interleukin-1 (IL-1) receptors following treatment of mouse AtT-20 pituitary tumor cells with corticotropin-releasing factor (CRF). In the present study, we determined the modulation of IL-1 receptors and adenylate cyclase activity in AtT-20 cultures following treatment with CRF, isoproterenol, forskolin, somatostatin and dexamethasone. CRF, isoproterenol and forskolin dose-dependently increased cAMP production and [125I]IL-1 alpha binding. In contrast, somatostatin and dexamethasone significantly inhibited CRF-stimulated cAMP production and decreased both basal and CRF-mediated increases in [125I]IL-1 alpha binding. Parallel modulation of IL-1 receptors by agents that stimulate (CRF, isoproterenol and forskolin) or inhibit (somatostatin) cAMP production in AtT-20 cells suggest the importance of this second messenger in regulating IL-1 receptors.

Adrenalectomy but not gonadectomy affects rat pineal beta-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 beta-adrenergic receptors is independent from gonadal control.

Alpha-adrenergic stimulation of growth hormone release in perifused rat anterior pituitary reaggregate cell cultures

It has been previously shown that beta-adrenergic agonists stimulate growth hormone (GH) release from perifused rat anterior pituitary cell aggregates cultured in serum-free defined medium for 5-6 days. The present data show that the natural beta-agonist epinephrine (EPI) stimulates GH release through an additional alpha-adrenergic mechanism. The involvement of this mechanism was suggested by the following findings. The intrinsic activity of EPI, at concentrations greater than 10 nM, was significantly higher than that of isoproterenol (ISO) in stimulating GH release. Phenylephrine (PHE), a specific agonist of alpha 1-adrenergic receptors, provoked a significant rise of GH release. The effect was concentration dependent between 100 nM and 10 microM. The stimulatory effect of EPI and PHE was lowered, respectively blocked, by low concentrations of the potent alpha 1-adrenergic antagonist prazosin. The EPI-induced GH release could be totally blocked only by administration of both alpha- and beta-receptor antagonists. Under the same conditions and using concentrations up to 1 microM, the alpha 2-agonist clonidine had no or only a slight stimulatory effect; dopamine had no effect. Administration of both PHE and ISO resulted in a more than additive stimulation of GH release. The effectiveness of PHE but not clonidine, together with the high potency of the alpha 1-blocker prazosin suggest that the alpha-adrenergic receptor is predominantly of the alpha 1-subtype. When tested on days 1, 3, 6 and 8 in culture, both alpha- and beta-adrenergic responses appeared to be higher in the presence of the glucocorticoid dexamethasone compared to the responses in the absence of dexamethasone.(ABSTRACT TRUNCATED AT 250 WORDS)