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Myometrial Contracture-Related Increases in Plasma Adrenocorticotropin in Fetal Sheep in the Last Third of Gestation are Abolished by Maintaining Fetal Normoxemia^*

Laboratory for Pregnancy and Newborn Research, Department of Physiology, New York State College of Veterinary Medicine (P.W.N., C.K.), Cornell University Ithaca, New York 14853
Department of Obstetrics and Gynaecology (B.R. W., J.G.A.), State University Groningen, The Netherlands

Address all correspondence and requests for reprints to: Dr. Peter W. Nathanielsz, M.D., Ph.D., Director, Laboratory for Pregnancy and Newborn Research, NYS College of Veterinary Medicine, Department of Physiology, Cornell University, Ithaca, New York 14853.

Abstract

Low amplitude, long-lasting epochs of myometrial activity, contractures, occur throughout the majority of pregnancy in all species studied to date. Contractures are associated with a fall in fetal oxygenation and changes in fetal behavioral state. In the present study we observed that contractures produced by the administration of 70 mil oxytocin iv to the pregnant ewe at 125–139 days gestational age (term 145–150 days) result in a fall in fetal carotid arterial PO₂ of approximately 2.5 mm Hg and are followed by a rise in fetal carotid arterial plasma ACTH of 16.3 ± 9.6 pg-ml^-1 (mean ± SEM). When the contractu re-induced fal! in fetal arterial PO₂ was prevented by administration of oxygen to the ewe, fetal ACTH did not rise after the contracture. In conclusion, these observations demonstrate that the relatively small fall in fetal PO₂ that accompanies a contracture can be sensed by the fetus and is an essential part of the stimulus to the increased secretion of fetal ACTH that accompanies a contracture. These findings support the view that myometrial activity is one of the factors that influence fetal ACTH secretion. (Endocrinology 129:1709–1713,19911

Footnotes

^* This work was supported by the NIH Grant HD 21350, and a grant from the Ter Meulen Fund, Royal Netherlands Academy of Arts and Sciences (toB.R.W,).

Received November 2, 1991.

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