Development of the hypothalamic-hypophysial-gonadotrophic activities in fetal rats.

Pituitary responsiveness to LHRH and anti-LHRH serum was investigated in fetal rats aged 18.5-22.5 days. Synthetic LHRH injection in utero into fetuses brought about a remarkable depletion of pituitary-LH with a corresponding increase of serum-LH on day 18.5. On the contrary, anit-LHRH serum administration to day-20.5 fetuses caused a significant augmentation of pituitary-LH 1 day later. These data indicate that LH-gonadotrophs respond to LHRH even on day 18.5, and that endogenous LHRH begins to affect LH gonadotrophs on day 20.5.