A Two-Step Mechanism by Which Corticotropin- Releasing Hormone Releases Hypothalamic β-Endorphin: The Role of Vasopressin and G-Proteins*

Abstract

It is well established that in the pituitary gland corticotropin-releasing hormone (CRH) stimulates the release of beta-endorphin (beta-E) via a cAMP-linked mechanism. Studies of the mechanisms underlying the CRH stimulation of beta-E release from rat hypothalamic slices perifused in vitro are reported in this paper. The data indicate that both a cAMP-dependent and non-cAMP-dependent mechanism mediate the action of CRH in the hypothalamus. The presence of a cAMP-linked mechanism was suggested by the finding that cholera toxin (0.1-10 nM) and forskolin (2.5 x 10(-6) M), both of which act to raise intracellular cAMP levels, stimulated the release of beta-E. In both cases, no further stimulation was seen upon addition of CRH (10(-8)M). However, it was also found that preincubation of the tissue with pertussis toxin (PTX; 100 ng/ml) prevented both the CRH- and forskolin-stimulated release of beta-E. This indicated that, in addition to the cAMP-linked mechanism, a further messenger system which is connected to a PTX-sensitive G-protein may also play a role. The latter observation also implied that a further substance, which utilizes a separate second messenger system, might be involved in the CRH stimulation of beta-E release. In this regard the role of arginine vasopressin (AVP) was investigated due to the known interaction between CRH and AVP in the pituitary gland. AVP (10(-12) to 10(-6)M) itself potently and dose-dependently stimulated beta-E release, producing a maximal increase of 220% above basal levels. The AVP-induced release of beta-E was abolished in PTX-pretreated hypothalami. The apparently obligatory requirement of AVP for the CRH-stimulation of beta-E release was illustrated by the finding that blockade of AVP receptors using the AVP antagonist d(CH2)5 [Tyr(OEt)2,Val4]-AVP almost completely attenuated the CRH-stimulated release of beta-E. Furthermore, in the presence of a high concentration of AVP (10(-6)M) no further stimulation of release was seen with CRH (10(-8)M). These data therefore strongly indicate that CRH acts via the intermediacy of AVP to release beta-E from hypothalamic slices in vitro and that two separate second messenger systems are involved: a cAMP-linked mechanism connected to a cholera toxin-sensitive G-protein (CRH) and a second system linked to a PTX-sensitive G-protein (AVP).

Hypothalamic-Pituitary-Adrenal Axis Suppression and Inhaled Corticosteroid Therapy

“…A lateral group of CRH neurons is primarily involved in connections with the brainstem noradrenergic centers. Some paraventricular neurons mediate an analgesic effect by projecting to the arcuate nucleus and to pain control areas in the brainstem and spinal cord, initiating release of POMC-derived opioid peptides [35,36]. These peptides simultaneously inhibit the stress system by participating in the negative-feedback-loop mechanisms suppressing CRH and norepinephrine secretion.…”

Organization and Integration of the Endocrine System: The Arousal and Sleep Perspective

“…PVN CRH and AVP neurons also send projections to and activate pro-opiomelanocortin (POMC)-containing neurons in the arcuate nucleus of the hypothalamus, which in turn project to the PVN CRH and AVP neurons, innervate LC/NE-sympathetic neurons of the central stress system in the brain stem, and terminate on pain control neurons of the hindbrain and the spinal cord. [3][4][5]30] …”

“…[14,30,61] Activation of the stress system stimulates hypothalamic POMCderived peptides, such as a-melanocyte-stimulating hormone and b-endorphin, which reciprocally inhibit the activity of both central components of the stress system and, through projections to the hindbrain and the spinal cord, produce analgesia.…”

Hypoglycemia-induced Suppression of Luteinizing Hormone (LH) Secretion in Intact Female Rhesus Macaques: Role of Vasopressin and Endogenous Opioids

“…Naloxone can reverse the CRH inhibitory activity on GnRH release (Gindoff and Ferin, 1987;Ferin, 1999), indicating that opioids are also involved in stress-induced suppression of LH secretion. The complex interaction of these factors is shown by the observation that CRHinduced release of endorphin from the hypothalamus in vitro requires AVP as an obligatory mediator (Burns et al, 1989).…”