No abstract

In six ewes heat stressed from 39 to 125 days gestation and studied in a normothermic environment at 135 days, fetal and placental masses were less than in control sheep (1,645 vs. 3,112 and 149 vs. 356 g, respectively, P less than 0.01). Umbilical glucose uptakes (Rf,UP) were measured keeping maternal arterial plasma glucose at 70 mg/dl at spontaneously occurring fetal plasma glucose values (state A) and at two additional fetal glucose levels, to determine the transplacental glucose difference (delta) vs. Rf,UP relation. At normal delta of 49.2 mg/dl, Rf,UP was less in the experimental group (3.2 vs. 5.6 mg.min-1.kg fetus-1, P less than 0.05). Differences in placental perfusion and glucose consumption could not account for this result, thus indicating a reduced placental glucose transport capacity. In state A, fetal hypoglycemia enlarged significantly (P less than 0.01) the delta to 56.7 mg/dl and increased Rf,UP approximately 50% over the Rf,UP at a normal delta. In heat-induced fetal growth retardation, fetal hypoglycemia increases the flux of maternal glucose across a placenta with reduced glucose transport capacity.

A method is described for the simultaneous estimation of uterine and umbilical blood flows and oxygen uptakes. A test stubstance, antipyrine, was infused at constant rate in the fetal circutlation. About 50 min. after starting the infusion a steady state was attained in which the rate of transplacental diffusion of the test substance was equal, blut for small corrections, to the rate of infusion. During the steady state, blood samples were collected from uterine and umbilical arteries and veins and analyzed for antipyrine and oxygen. Flows and oxygen uptakes were calculated according to Fick's principle. Thie results of sixteen experiments on sheep and goats sh1ow that: (1) transplacental diffusion of antipyrine is mainly flow‐limited, (2) the placenta simulates a concturrent system of exchange, and (3) the oxygen uptakes of the fetus and the utero‐placental mass were, in many cases, of similar magnitude.

No 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.