AJP - Endocrinology and Metabolism, Vol 270, Issue 3 E477-E482, Copyright © 1996 by American Physiological Society
Effect of chronic hypoxia on myometrial responsiveness in the pregnant rat
J. W. Rhee, L. D. Longo, W. J. Pearce, N. H. Bae, G. J. Valenzuela and C. A. Ducsay
Department of Physiology, Loma Linda University, School of Medicine, California 92350, USA.
Mechanisms involving the timing of normal parturition are not well
understood in most animal species. To gain a greater understanding of the
mechanisms, we employed hypoxia to perturb the normal system of
parturition. The present study was designed to investigate the effects of
chronic hypoxia on myometrial contractility in the near-term pregnant rat.
Rats were exposed to room air (control) or to continuous hypoxia (10.5% O2)
either from experimental days 19 through 21 (2-day exposure) or from
experimental days 15 through 21 (6-day exposure). On day 21, blood was
collected for hormone assays, and the uterine horns were collected from
each dam. One horn was snap-frozen in liquid nitrogen for oxytocin (OT)
receptor analysis, and the other was used for in vitro assessment of
myometrial contractile responses to cumulative doses of OT or arginine
vasopressin (AVP). Hypoxic exposure resulted in approximately 60% reduction
of the maximal myometrial contractile response to OT and a significant
reduction in OT binding sites from 256.9 +/- 34.9 to 84.9 +/- 21.3 fmol/mg
protein (P<0.01). In contrast, the contractile response to AVP was
unaffected after exposure to chronic hypoxia (P> 0.05). Additionally, we
observed no difference in the plasma concentrations of estrogen,
progesterone, and corticosterone. We conclude that chronic hypoxia
decreased the effectiveness of OT-specific contractile mechanisms, at least
partially through a decrease in OT binding sites.
