Estrogens in the Uteroovarian, Uterine, and Peripheral Plasma in Pregnant Rhesus Monkeys

Estrone and estradiol were measured in the uteroovarian vein (UOV), uterine vein (UV) and peripheral plasma at Days 22, 42, 76 and 157 of gestation in the rhesus monkey. Based on UOV and UV estrogen levels, both the ovary containing the corpus luteum (CL) and the placenta were secreting estrone and the placenta estradiol at Day 22 of gestation. During the rest of gestation the fetoplacental unit was the major source of these estrogens. UV estradiol increased progressively and substantially from Day 22 (mean = 285 pg/mI) to Day 76 (4,106 pg/mI), but decreased by Day 157 (552 pg/mI). UV estrone, on the other hand, decreased markedly from Day 22 (1,746 pg/mI) to Day 42 (208 pg/mI), but then increased gradually throughout the rest of gestation (Day 157 = 1,381 pg/mI). Although UV estrone was considerably higher than UV estradiol at Days 22 and 157, the peripheral levels of these estrogens were essentially the same. These data indicate that: 1) the ovary containing the CL is producing estrogens during early gestation, but not during mid or late gestation; 2) the placenta or fetoplacental unit produces estrogens throughout most of gestation; 3) during the latter half of pregnancy there is a decrease in placental production of estradlol concurrent with an increase in placental production of estrone, the significance of which may be related to the initiation of parturition and 4) the concentrations of estrone in the reproductive vasculature are considerably higher than those of estradiol during early (Day 22) and late (Day 157) gestation; peripheral estrone and estradiol concentrations at these times, however, are essentially the same.