Effects of corticotropin-releasing factor, neurohypophyseal peptides, and catecholamines on pituitary function

In freely moving rats, ovine corticotropin-releasing factor (CRF) and rat CRF, which are equipotent in stimulating adrenocorticotropin (ACTH) release, can exert this effect after either i.v. or intracerebroventricular (i.c.v.) administration. Oxytocin and epinephrine also elevate plasma ACTH levels, an effect that is abolished by immunoneutralization of endogenous CRF. Inasmuch as oxytocin and epinephrine show additivity with CRF, these results suggest that these two secretagogues stimulate ACTH secretion in vivo by interacting with endogenous CRF. Apart from its effect on ACTH release, CRF injected i.c.v. markedly inhibits luteinizing hormone (LH), but not follicle-stimulating hormone, secretion in rats in the absence of circulating levels of steroids. A similar effect is observed after i.c.v. administration of sauvagine, a peptide analogous to CRF, whereas arginine vasopressin exhibits lower potency and shorter duration of action than CRF. Because these peptides do not modify LH release by cultured pituitary cells, they probably lower plasma LH levels through centrally mediated mechanisms. These results indicate that CRF can exert a broad spectrum of action to regulate pituitary function directly or indirectly.