Effect of chronic hypoxia on myometrial responsiveness in the
pregnant rat.
Rhee, Joon W., Lawrence D. Longo, William J. Pearce, Nicholaus H. Bae,
Guillermo G. Valenzuela, and Charles A. Ducsay.
Center for Perinatal Biology, Departments of Physiology,
Pediatrics, and Obstetrics & Gynecology, Loma Linda University,
School of Medicine, Loma Linda, CA 92350
APStracts 2:0222E, 1995.
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. Methods Rats were exposed to room air (control),
or to continuous hypoxia (10.5% O2) either from E19 through E21 (2D
exposure) or from E15 through E21 (6D 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, while the other was used for in
vitro assessment of myometrial contractile responses to cumulative
doses of OT or arginine-vasopressin (AVP). Results Hypoxic exposure
resulted in approximately 60% reduction of the maximal myometrial
contractile response (TMAX) to OT and a significant reduction in OT
binding sites from 256.9 34.9 to 84.9 21.3 fM/mg protein (p <
0.01). In contrast, the contractile response to AVP was unaffected
following exposure to chronic hypoxia (p > 0.05). Additionally,
we observed no difference in the plasma concentrations of estrogen,
progesterone, and corticosterone. Conclusion Chronic hypoxia
decreased effectiveness of oxytocin-specific contractile mechanisms,
at least partially through a decrease in OT binding sites.
Received 11 May 1995; accepted in final form 30 October 1995.
APS Manuscript Number E215-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95