Uteroplacental blood flow and uteroplacental shunt rates in normal and prolonged pregnancies in rats.

To reveal the regulatory function in uteroplacental blood flow we measured, using the method of double tracer microspheres, the rates of uteroplacental blood flow (UPBF) and uteroplacental shunt (UP-shunt) in SD-strain rats of normal and prolonged pregnancy. (1) In the group of rats of normal pregnancy, the rate of UPBF attained a peak on the 20th day of gestation, while the UP-shunt rate was highest on the 18th day of gestation. (2) In the progesterone-induced prolonged pregnancy group, the rate of UPBF remained at an 8% level until the the 22nd day, i.e., the first day of prolonged pregnancy, and dropped to 6.6% on the 23rd day. The UP-shunt rate in the progesterone-administered group was about 27% on the 20th day, more favorable than the corresponding rate in the normal group, but thereafter rapidly decreased. The rate of increase in fetal body weight in this group became lower, showing a fetal death rate of 4.6%. (3) The decreases in placental alkaline phosphatase and leucine aminopeptidase examined as markers of placental function lagged behind the fall in the UP-shunt rate. On the 23rd day of gestation when the rates of UPBF and UP-shunt dropped, the decreases in their placental enzyme activities were remarkable.