Modulation of ovine fetal adrenocorticotropin secretion by
androstenedione and 17[beta]-estradiol.
Saoud, Christine J., and Charles E. Wood.
Department of Physiology, University of Florida College of
Medicine
APStracts 3:0392R, 1996.
Parturition in sheep is initiated by increases in activity of the
fetal hypothalamus-pituitary-adrenal axis. We have previously
reported that cortisol negative feedback efficacy is decreased at the
end of gestation. The present study was designed to test the
hypothesis that increasing plasma estrogen and/or androgen
concentrations in the fetus might increase plasma ACTH concentration,
either by stimulating ACTH secretion or by altering the negative
feedback effect of cortisol on ACTH. Fetal sheep were chronically
catheterized and treated with no steroid (control), 17[beta]
-estradiol, or androstenedione (each approximately 0.24 mg/day). After
catheterization and implantation of steroid pellet, fetuses were
subjected to two short (10 min) periods of sodium nitroprusside
-induced hypotension with or without pretreatment with intravenous
infusion of hydrocortisone sodium succinate -0.5 [mu]g/min) to test
fetal ACTH responsiveness to stress and cortisol negative feedback
efficacy. Estradiol treatment significantly increased basal plasma
ACTH and cortisol concentrations relative to control fetuses, but did
not interfere with the inhibition of ACTH secretion by cortisol.
Fetal plasma ACTH responses to hypotension were significantly
suppressed approximately 60% in both control- and estradiol-treated
groups. Androstenedione treatment significantly increased basal fetal
plasma ACTH and decreased basal fetal plasma cortisol concentration.
Androstenedione did not alter stimulated levels of fetal ACTH, but
did block the inhibition of stimulated ACTH by cortisol. We conclude
that increased fetal cortisol and ACTH secretion at the end of
gestation may be due to the combined effects of the gonadal steroids
in that estradiol increases basal plasma ACTH secretion while
androstenedione reduces cortisol negative feedback efficacy.
Received 28 March 1996; accepted in final form 14 October 1996.
APS Manuscript Number R186-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996