Effect of atrial natriuretic factor on corticotrophin-releasing hormone-induced adrenocorticotrophin release in the mature ovine foetus.

Abstract

1. Atrial natriuretic factor (ANF) and its analogues have been shown previously to inhibit corticotrophin-releasing hormone (CRH)-induced adrenocorticotrophin (ACTH) release, both in vivo and in vitro, and it has been suggested that ANF may be a, or the, physiological ACTH-inhibitory factor. To determine whether ANF is relevant in the regulation of ACTH secretion in the ovine foetus, the present study examines the effect of ANF on CRH-stimulated ACTH release in the mature ovine foetus. 2. Five chronically cannulated foetuses, studied between 129 and 140 days of gestation (term 145-150 days), received intraarterial infusions of ovine CRH (4 micrograms/h) 120 min after the start of a sustained infusion of human ANF5-28 (10 micrograms/h) or saline (1.2 mL/h). Appropriate control experiments were performed, with foetuses receiving ANF or saline infusion only. CRH, ACTH, ANF and cortisol levels were measured by sensitive and specific radioimmunoassays. Each animal received all four treatments, with the order being randomized and 2-3 days being allowed between experiments. 3. It was found that pretreatment (120 min) with ANF5-28 (at levels devoid of significant cardiovascular actions) had no effect on mean basal or peak ACTH and cortisol levels during CRH infusion. Given the current experimental parameters, these results suggest that ANF does not acutely modulate basal or CRH-stimulated ACTH and cortisol release in the mature ovine foetus.