Renal hypertension and pregnancy in the sheep. I. behavior of uteroplacental vasomotor tone during mild hypertension.

The progressive changes in arterial pressure and uteroplacental hemodynamics were studied in 13 pregnant sheep from about the eightieth gestational day. All animals were followed to term. The results revealed a progressive increase in uteroplacental blood flow as the pregnancy progressed in the seven control animals. In six of the animals, mild hypertension was induced by unilateral renal artery constriction at about the one hundred fifteenth day. Following the induction of mild hypertension, there was a transient increase in uteroplacental vascular resistance and a reduction in uteroplacental blood flow. The arterial pressure remained significantly increased throughout the remainder of the gestation.