Relative importance of nitric oxide and carbon monoxide in regulating the ACTH response to immune and non-immune signals

Role of hypothalamic corticotropin-releasing factor in mediating alcohol-induced activation of the rat hypothalamic-pituitary-adrenal axis

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis through brain-based mechanisms in which endogenous corticotropin-releasing factor (CRF) plays a major role. This review first discusses the evidence for this role, as well as the possible importance of intermediates such as vasopressin, nitric oxide and catecholamines. We then illustrate the long-term influence exerted by alcohol on the HPA axis, such as the ability of a first exposure to this drug during adolescence, to permanently blunt neuroendocrine responses to subsequent exposure of the drug. In view of the role played by CRF in addiction, it is likely that a better understanding of the mechanisms through which this drug stimulates the HPA axis may lead to the development of new therapies used in the treatment of alcohol abuse, including clinically relevant CRF antagonists.

Comparison between the influence of the intravenous and intracerebroventricular injection of a nitric oxide donor on adrenocorticotropic hormone release and hypothalamic neuronal activity

We investigated the ability of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1) to release adrenocorticotropic hormone (ACTH) and up-regulate hypothalamic neurones following its intravenous (i.v.) injection. i.v. SIN-1 (0.2-1.8 mg/kg) produced dose-related increases in plasma ACTH levels which were blocked by prior neutralization of endogenous corticotropin-releasing factor (CRF) but not by vasopressin antibodies. In contrast, the intracerebroventricular (i.c.v.) injection of 50-microg SIN-1 released significantly larger amounts of ACTH, a response blunted by either CRF or vasopressin antibodies. While i.c.v. SIN-1 markedly up-regulated transcripts of the immediate early gene NGFI-B in the paraventricular nucleus (PVN) of the hypothalamus, no such response was observed following the i.v. injection of up to 2.0 mg/kg SIN-1. Finally, we found no evidence that the influence of the peripheral administration of SIN-1 on ACTH secretion is mediated by altered pituitary responsiveness to CRF or vasopressin. The fact that NO has a profound hypotensive influence in the periphery suggests that it may have released ACTH through this mechanism, although the absence of PVN neuronal response in regions that are activated by decreased blood pressure casts some doubt on this hypothesis. As the systemic injection of arginine derivatives that block NOS activity potently augment the ACTH response to circulating pro-inflammatory cytokines or vasopressin, the present findings indicate that the mechanisms responsible for this phenomenon are distinct from those responsible for ACTH released by i.v. SIN-1.