The effect of progesterone on estrogen-induced uterine blood flow

The effect of progesterone on estrogen-induced uterine blood flow was investigated in repeated experiments in seven nonpregnant, oophorectomized ewes with chronically implanted electromagnetic flow probes and catheters inserted into branches of the uterine arteries. Administered alone, progesterone has no effect on base-line uterine blood flow. Following intramuscular injection of progesterone (3 to 5 mg-per kilogram of body weight), peak uterine blood flow responses to 1 microng of estradiol-17beta were suppressed by 25 per cent compared to those of control animals. Direct intra-arterial infusion of progesterone, at concentrations sufficient to reproduce uterine venous levels observed in late pregnancy in the sheep, inhibited estrogen-induced uterine blood flow by 20 per cent. The findings support the hypothesis that progesterone modulates the estrogen-induced flow responses in both the pregnant and nonpregnant uterine vascular bed.