Endocrine responses of the ovine fetus to sustained hypoxemic
stress after chronic fetal placental embolization.
Gagnon, Robert, Jun Murotsuki, John R. G. Challis, Larry Fraher, and
Bryan S. Richardson.
Department of Obstetrics and Gynaecology and of Physiology, MRC
Group in Fetal and Neonatal Health and Development, the University of
Western Ontario, London, Ontario, and Departments of Physiology and
Obstetrics and Gynecology, University of Toronto, Toronto, Ontario,
Canada
APStracts 4:0013E, 1997.
The purpose of this study was to determine the endocrine and
circulatory responses of the ovine fetus, near term, to sustained
hypoxemic stress superimposed on chronic hypoxemia. Fetal sheep were
chronically embolized (n=7) for 10 days between 0.84 and 0.91 of
gestation via the descending aorta until arterial oxygen content was
decreased by 30%. Control animals (n=8) received saline only. On
experimental day 10, both groups were embolized over a 6 hour period
until fetal arterial pH decreased to 7.00. Regional distribution of
lower body blood flows was measured on day 10, before and at the end
of acute embolization. On day 10, the chronically embolized group had
lower arterial oxygen content (p<0.05), pO2 (p<0.01)
and placental blood flow (p<0.05) than controls, and higher
prostaglandin E2 (PGE2) and noradrenaline plasma concentrations (both
p<0.05). In response to a superimposed sustained hypoxemic
stress, there was a two-fold greater increase in PGE2 in the
chronically embolized group compared with the control group
(p<0.05). However, the increase in fetal plasma cortisol in
response to superimposed hypoxemic stress was similar in both groups
despite significantly lower adrenocorticotrophin and adrenal cortex
blood flow responses in the chronically hypoxemic group (both
p<0.05). We conclude that PGE2 response to a sustained
superimposed reduction in placental blood flow leading to metabolic
acidosis, is enhanced under conditions of chronic hypoxemia and may
play an important role for the maintenance of the fetal cortisol
response to an episode of superimposed acute stress.
Received 8 July 1996; accepted in final form 6 January 1997.
APS Manuscript Number E317-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 19 February 1997