AJP - Regulatory, Integrative and Comparative Physiology, Vol 272, Issue 4 1128-R1134, Copyright © 1997 by American Physiological Society

ARTICLES

Modulation of ovine fetal adrenocorticotropin secretion by androstenedione and 17beta-estradiol

C. J. Saoud and C. E. Wood
Department of Physiology, University of Florida College of Medicine, Gainesville 32610-0274, USA.

Parturition in sheep is initiated by increases in activity of the fetal hypothalamic-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 adrenocorticotropic hormone (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), 17beta-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 microg/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.

This article has been cited by other articles:

				C. E. Wood and H. Tong Central nervous system regulation of reflex responses to hypotension during fetal life Am J Physiol Regulatory Integrative Comp Physiol, December 1, 1999; 277(6): R1541 - R1552. [Abstract] [Full Text] [PDF]

				S. C. Purinton, H. Newman, M. I. Castro, and C. E. Wood Ontogeny of estrogen sulfatase activity in ovine fetal hypothalamus, hippocampus, and brain stem Am J Physiol Regulatory Integrative Comp Physiol, June 1, 1999; 276(6): R1647 - R1652. [Abstract] [Full Text] [PDF]

				M. Keller-Wood ACTH responses to hypotension and feedback inhibition of ACTH increased by chronic progesterone treatment Am J Physiol Regulatory Integrative Comp Physiol, January 1, 1998; 274(1): R81 - R87. [Abstract] [Full Text] [PDF]

				M. Keller-Wood Evidence for reset of regulated cortisol in pregnancy: studies in adrenalectomized ewes Am J Physiol Regulatory Integrative Comp Physiol, January 1, 1998; 274(1): R145 - R151. [Abstract] [Full Text] [PDF]