Circulatory Changes in the Reproductive Tissues of Ewes during Pregnancy

Abstract

The blood flows to reproductive organs were measured by means of radionuclide-labeled microspheres in 24 pregnant ewes with gestational ages ranging from 38 to 141 days. The microspheres were injected in the left ventricle of the non-anesthetized animal 4–7 days after surgery and while uterine blood flow was recorded continously by means of electromagnetic probes on both uterine arteries. The blood flow to ovaries with corpus luteum was maximum in early pregnancy and greater than in ovaries without corpus luteum. Placental blood flow increased from ∼30 to ∼300 ml/min during the stage of placental growth (40–90 days). In the last 50 days of pregnancy placental weight declined, whereas placental flow continued to rise and attained ∼1,500 ml/min near term. The growth curves of fetal weight and placental blood flow followed a similar pattern, but the early increase in placental flow was more rapid than the increase in fetal weight. Hence placental flow per gram of fetus was larger in early pregnancy (∼9 ml/min·g) than near term (∼0.25 ml/min·g). In twin pregnancies the placenta of each fetus received a smaller blood flow than the placenta of a singleton of comparable age. Mammary blood flow demonstrated no change until the last 60 days, when it increased from ∼10 to ∼200 ml/min. This phenomenon coincided with an increase in mammary weight and the final progressive increase of placental blood flow.