Fetal and maternal endocrine responses to prolonged reductions in uterine blood flow in pregnant sheep.

To examine the effects of sustained (48-hour) hypoxemia on fetal and maternal adrenocorticotropic hormone concentrations and on maternal progesterone, uterine blood flow was reduced in eight sheep at day 128 of pregnancy by means of an adjustable Teflon clamp placed around the maternal common internal iliac artery. Control measurements were made in four animals in which the vascular clamp was not adjusted. Fetal PaO2 fell from 20.6 +/- 1.1 mm Hg (mean +/- SEM) to 16.6 +/- 0.6 mm Hg within 1 hour after application of the clamp and remained suppressed during 48 hours. There was a transient acidemia at 1 to 2 hours that had corrected by 8 hours. Fetal adrenocorticotropic hormone levels rose from 24 +/- 6 to 1320 +/- 205 pg/ml at 2 hours but decreased by 16 hours. Measured by high-pressure liquid chromatography, more than 95% of immunoreactivity corresponded to adrenocorticotropic hormone1-39. Fetal cortisol levels rose by 6 hours and remained elevated through 48 hours. Maternal adrenocorticotropic hormone, cortisol, and progesterone levels were unchanged during the study period. We conclude that fetal hypoxemia-acidemia after restriction of uterine blood flow provokes fetal adrenocorticotropic hormone release, but the elevation in adrenocorticotropic hormone is not sustained. However, the level of fetal cortisol rises progressively, consistent with fetal adrenal activation.