Placental and serum hormone changes during the second half of pregnancy in the hamster

The concentrations of androgen, estrogen, progesterone, and prolactin-like hormones in serum, placentae, and media from placental incubations during the second half of pregnancy in the hamster were determined. Concentrations of prolactin-like activity in serum, placentae, and media from placental incubations increased from Day 8 to Day 14 of gestation. On Day 16 of pregnancy the content and in vitro release of placental prolactin-like activity declined; however, serum prolactin-like activity increased. The in vitro release of 3H-protein by hamster placentae showed gestational changes resembling the pattern of in vitro placental lactogen release. Serum and placental content of progesterone increased from Day 8 to Day 14 of gestation and declined from Day 14 to Day 16. In vitro placental progesterone release increased from Day 8 to Day 12 and declined from Day 12 to Day 16. Serum estrogen levels were elevated during the second half of pregnancy, whereas serum androgen levels were minimal. Neither estrogen nor androgen production by hamster placentae could be detected.