Placental and nonplacental drainage of the uterus in the pregnant rhesus monkey

Abstract

The proportion of placental to nonplacental drainage of the pregnant uterus of the anesthetized term rhesus monkey was assessed by means of a steady-state transplacental diffusion technique involving infusion of tritiated water at a constant rate into the fetal circulation and determination of the concentrations of radioactivity in the principal veins draining the uterus. No placental blood appeared to be drained through the hypogastric veins. There was considerable variation in the proportion of placental to nonplacental blood in each of the ovarian veins among the 6 animals studied. Ligation of one of the ovarian veins invariably resulted in a decrease in the transplacental clearance of tritiated water. It is concluded that blood samples from the ovarian veins of the pregnant rhesus monkey are generally not representative of the venous drainage of the placentas, which poses an important problem in the application of a diffusion equilibrium technique in this primate for measurement of uterine blood flow and consumption of gases based on the Fick principle.