Placental and luteal steroidogenesis in the pregnant rhesus monkey

Progesterone, 20alpha-dihydroprogesterone, estrone and estradiol-17beta concentrations were estimated by radioimmunoassay in blood plasma from uterine, uteroovarian and femoral veins of rhesus monkeys (Macaca mulatta) on days 22, 49, 128 and 160 of gestation. Steroids were consistently more concentrated in uterine and uteroovarian that in femoral venous plasma and in many cases levels in the uteroovarian vein were also higher than those in the uterine vein indicating luteal secretion of both progestins and estrogens thoughout gestation. In some animals, however, the corpus luteum appeared quiescent. As reflected in the decline in the uterine venous progesterone/estradiol-17beta concentration ratio, a shift in steroid contribution from the uterus and its contents occurred between days 22 and 49 of gestation with progesterone declining more rapidly than estradiol-17beta. Progesterone/20alpha-dihydroprogesterone was higher in both uterine and uteroovarian than in femoral venous plasma suggesting peripheral metabolism of progesterone to 20alpha-dihydroprogesterone.