The persistence of placental remnants, beyond the normal period of gestation, in rats ovariectomised at day 12 of pregnancy.

The uterus, mammary glands and vaginal epithelium were examined in rats ovariectomised at day 12 of pregnancy and killed between 10 and 16 days later, and in a group of normal post partum rats. All the animals were injected with tritiated thymidine one hour before death. Some placental remnants persisted in all the ovariectomised animals and were associated with incorporation of tritiated thymidine in the uterine epithelium and smooth muscle. A pronounced cellular infiltration occurred in the endometrium and metrial gland of the normal post partum animals, with a marked increase in nuclear labelling. In comparison, the cellular reaction in the endometrium of the ovariectomised animals was delayed and very much reduced, and there was no reaction in the metrial gland. The breasts of the ovariectomised animals were secreting up to 12 days after operation; in all the ovariectomised animals the vaginal epithelium was of low, stratified squamous form, with nuclear labelling in the basal layers. The results are discussed in relation to the possible endocrine environment prevailing in the ovariectomised animals, and in relation to the possible factors affecting the influx of blood-borne cells to the uterus.