Estrogens, Progesterone and Chorionic Gonadotropin in Pregnant Rhesus Monkeys

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Abstract
Ten adult female rhesus monkeys were mated 11 days after the onset of menstruation. Blood samples were taken on the first day of mating and subsequently at 10-day intervals throughout gestation as well as one week postpartum. Plasma levels of 17β-estradiol and progesterone were determined by radioimmunoassay and competitive protein-binding assay, respectively. Continuous daily urine collections were made in early (days 7–35) and late (ISO days until 7 days post-partum) pregnancy for quantitation of chorionic gonadotropin and estrone excretion. Estradiol concentrations in plasma were elevated 3 times during the fertile cycle and pregnancy: (1) preovulatory, (2) at 20 days in pregnancy, and (3) during a plateau that was maintained from day 100 until term. The 20-day estradiol peak was associated with the time of highest chorionic gonadotropin activity. During the initial 40 days of gestation, peak levels of plasma progesterone were associated with nadirs in estradiol and vice versa. However, both progesterone and estradiol levels increased progressively during mid-gestation with little deviation from the 90th through the 150th day of pregnancy. Urinary estrone rose about 3- fold during the 2 weeks immediately preceding parturition, reaching a peak 4 days before delivery, and fell precipitously during the last 3 days of pregnancy. Chorionic gonadotropin activity was not detected by bioassay of 24-hr urines collected during the final 2 weeks of gestation. (Endocrinology91: 896, 1972)

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