In vitro release of progesterone and estrone by the porcine placenta throughout gestation

In vitro release of progesterone (P4) and estrone (E1) by the porcine placenta was characterized at 12 days of gestation between d 20 and 110. Placental P4 rose linearly from d 25 to 40, plateaued between d 40 and 50, continued to increase to a peak concentration at d 100, then decreased sharply to d 110. Placental E1 decreased abruptly from d 30 to a nadir at d 40, then increased continuously from d 70 to peak values at d 110. This biphasic pattern for E1 mimicked the pattern observed in allantoic fluid and maternal plasma pools. Only trace amounts of testosterone (T) were measured at d 20, 50, 60, and 100, suggesting rapid aromatization of C19 steroids to estrogens. The results of this in vitro study indicate that the porcine placenta collected throughout gestation can release large quantities of P4, although the lack of an increase in systemic P4 suggests that under in vivo conditions P4 is utilized and/or metabolized within the uterus.