Presence of a chorionic gonadotrophin-like factor in mouse placental cultures during the second half of gestation.

Gonadotrophin-like activity in the cultures of mouse placentae, from Days 10 to 18 of gestation, was determined by using a sensitive mouse Leydig cell testosterone bioassay. The limit of detection of the bioassay was 0.05 mi.u. for the 2nd International Standard of hCG. Serial dilution of placental culture media gave dose-response curves parallel to those of the hCG standard. Gonadotrophin-like activity was detected in cultures of placentae from different stages of gestation, and a biphasic variation appeared: the first peak of activity was present at Day 12 (0.853 +/- 0.070 mi.u. hCG) while the second appeared on Day 17 of gestation (0.595 +/- 0.093 mi.u. hCG). These results suggest that the mouse placenta is capable of secreting a gonadotrophin-like factor in vitro.