A surgical technique for the selective extirpation of corpora lutea of pregnancy is described. Numbers of corpora lutea in the pregnant rat were reduced to three or less on the 5th day post coitum. Although two corpora lutea sufficed for the decidual response of nidation, three were the minimum for successful post-nidation pregnancy in a majority of rats.
Vaginal cornification usually followed reduction of the numbers of corpora lutea. If the ova implanted, no new corpora lutea were formed at this time, but if implantation was blocked oestrus was accompanied by ovulation and a prolonged period of leucocytic vaginal smears followed, presumably a pseudopregnancy. The results suggest that, even when progesterone levels from the reduced numbers of corpora lutea were still high enough to maintain pregnancy, they did not inhibit gonadotrophin secretion.