Corticotropin-releasing factor but not urocortin is involved in adrenalectomy-induced adrenocorticotropin release.

Urocortin, a new corticotropin-releasing factor (CRF)-related peptide, has been reported to have the ability to bind to CRF receptors and to stimulate adrenocorticotropin (ACTH) secretion from the rat anterior pituitary in vivo and in vitro. In this study, we examined the effect of intravenous administration of urocortin-antiserum to investigate the role of endogenous urocortin on ACTH secretion from rat anterior pituitary after adrenalectomy. Male Sprague-Dawley rats, which were maintained in a conscious and undisturbed condition, were administered non-immunized rabbit serum (NRS), CRF-antiserum or urocortin-antiserum at a volume of 1 ml/kg b.w. 15 min before the injection of secretagogues. Synthetic rat urocortin (2 microg/kg B.W.) increased plasma ACTH concentrations by about sixfold the basal concentration. The pretreatment with urocortin-antiserum but not CRF-antiserum abolished the urocortin-induced increase in plasma ACTH concentrations. In adrenalectomized rats, plasma ACTH concentrations were markedly increased at basal conditions, and rapidly reduced after the administration of CRF-antiserum. By contrast, administration of urocortin-antiserum did not alter ACTH secretion induced by adrenalectomy. Our results suggest that endogenous urocortin is unlikely to be involved in ACTH release in adrenalectomized rats.