EFFECT OF ATRIAL-NATRIURETIC-FACTOR ON CORTICOTROPIN-RELEASING HORMONE-INDUCED ADRENOCORTICOTROPIN RELEASE IN THE MATURE OVINE FETUS

1. Atrial natriuretic factor (ANF) and its analogues have been shown p reviously to inhibit corticotrophin-releasing hormone (CRH)-induced ad renocorticotrophin (ACTH) release, both in vivo and in vitro, and it h as been suggested that ANF may be a, or the, physiological ACTH-inhibi tory factor, To determine whether ANF is relevant in the regulation of ACTH secretion in the ovine foetus, the present study examines the ef fect 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 infusion s of ovine CRH (4 mu g/h) 120 min after the start of a sustained infus ion of human ANF(5-28) (10 mu g/h) or saline (1.2 mL/h), Appropriate c ontrol experiments were performed, with foetuses receiving ANF or sali ne infusion only, CRH, ACTH, ANF and cortisol levels were measured by sensitive and specific radioimmunoassays. Each animal received all fou r treatments, with the order being randomized and 2-3 days being allow ed between experiments. 3. It was found that pretreatment (120 min) wi th ANF(5-28) (at levels devoid of significant cardiovascular actions) had no effect on mean basal or peak ACTH and cortisol levels during CR H infusion, Given the current experimental parameters, these results s uggest that ANF does not acutely modulate basal or CRH-stimulated ACTH and cortisol release in the mature ovine foetus.