Rat chorionic gonadotropin: augmentation of bioactivity in the absence of the pituitary.

Significant gonadotropin-like bioactivity, as measured by rat interstitial cell testosterone assay, is present in the serum and placenta of pregnant rats. The patterns of activity for this putative rat chorionic gonadotropin (rCG) in serum and placenta are distinct from those observed for rat placental lactogen (rPL) radioreceptor activity. Placental and serum rCG (and rPL) activities are substantially increased, as are placental weights, following removal of the maternal pituitary on day 12 of pregnancy. These findings strengthen the evidence for the existence of a rat CG and suggest a novel role for the maternal pituitary in regulating placental function during normal gestation.