In vivo regulation of adrenocorticotrophin secretion in the immature ovine fetus. Modulation by ovine corticotrophin releasing hormone and arginine vasopressin.
This study investigates the in vivo regulation of ACTH secretion in the immature ovine fetus by AVP and oCRH. Previously we have demonstrated that whilst AVP-containing neurones are present from 42 days, oCRH-containing neurones cannot be detected in the fetal paraventricular nucleus or median eminence until after 90 or 100 days respectively. In acutely exteriorized fetuses aged between 64-90 days (n = 5), a haemorrhagic stress elicited a significant increase (P less than 0.01) in ACTH values. There was also a significant correlation between plasma ACTH and AVP concentrations in these fetuses. In chronically cannulated fetuses less than 100 days (n = 6) injection of AVP (200 ng) significantly elevated fetal plasma ACTH values at 10 min (P less than 0.01) post injection. Simultaneous injection of AVP (200 ng) and oCRH (10 micrograms) into these fetuses produced a plasma ACTH value that was significantly greater at 10 min (P less than 0.05) than the summed response obtained with separate injection of oCRH and AVP. When AVP and oCRH were injection in equimolar amounts to fetuses between 101-118 days, AVP (2 micrograms) was found to have a greater effect on ACTH than was oCRH (2 micrograms). Pretreatment with a specific vascular antagonist of AVP-d(CH2)5Tyr(Me)AVP failed to significantly inhibit the increase in mean arterial pressure associated with AVP (2 micrograms) injection but partially antagonized (P = 0.04) the decrease in fetal heart rate. The antagonist however completely abolished any effect of AVP on fetal plasma ACTH values. This study suggests that AVP most likely acts through receptors in the fetal pituitary with V1 characteristics.
MacIsaac
R J
RJ
Department of Physiology, University of Melbourne, Parkville, Australia.
Congiu
M
M
Levidiotis
M
M
McDougall
J G
JG
Wintour
E M
EM
D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology*; D005260:Female; D005312:Fetal Blood / Q000032:analysis; D005333:Fetus / Q000378:metabolism*; D005865:Gestational Age; D006340:Heart Rate, Fetal / Q000187:drug effects; D006470:Hemorrhage / Q000503:physiopathology; D007263:Infusions, Parenteral; D007275:Injections, Intravenous; D011247:Pregnancy; D013312:Stress, Physiological / Q000503:physiopathology; D013552:Swine
D001127:Arginine Vasopressin; D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone