Effects of long-term hypoxemia on pituitary-adrenal function in
fetal sheep.
Murotsuki, Jun, Robert Gagnon, Stephen G. Matthews, John R. G.
Challis.
Medical Research Council Group in Fetal and Neonatal Health and
Development, Department of Ob/Gyn and of Physiology, University of
Western Ontario, and Lawson Research Institute, St. Joseph's Health
Centre, London, Ontario, N6A 4V2; and, Department of Physiology,
University of Toronto, Toronto, Ontario, M5S 1A8 Canada
APStracts 3:0055E, 1996.
Effects of long-term hypoxemia on pituitary-adrenal function in fetal
sheep. To test the hypothesis that long-term hypoxemia causes
premature activation of the fetal pituitary-adrenal function, we
embolized the fetal side of the placenta in pregnant sheep and
examined the changes in concentrations of immunoreactive (ir-) ACTH,
cortisol and prostaglandin E2 (PGE2) in fetal plasma, and levels and
localization of pro-opiomelanocortin (POMC) mRNA in the pars distalis
and pars intermedia of the fetal pituitary. Twelve fetal sheep were
studied (6 embolized and 6 controls) for 21 days between 0.74 and
0.88 of gestation. Daily injections of nonradiolabelled microspheres
were given into the fetal abdominal aorta to decrease fetal arterial
oxygen content by 40-50 % of the pre-embolization values. In the
embolized group, concentrations of ir-ACTH, PGE2 and cortisol in
fetal plasma increased gradually and were significantly (p<0.05)
elevated above controls after day 10, day 16 and day 20,
respectively. POMC mRNA levels in the pars distalis of the fetal
pituitary were not different from controls, but were significantly
reduced in the pars intermedia (p<0.05). We conclude that levels
of POMC mRNA in the pars distalis are unchanged during long-term
hypoxemia possibly due to negative feedback effects of elevated
cortisol on the pituitary gland. During long-term fetal hypoxemia,
there is a differential regulation of POMC mRNA expression in the
pars distalis and pars intermedia.
Received 25 August 1995; accepted in final form 10 January 1996.
APS Manuscript Number E413-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96