[Histologic and biochemical studies of the uteri of ovariectomized gilts during the first two months of pregnancy after different hormone substitutions. 3. Local effects of the conceptus on the structure of the placenta and its modification by different progesterone and norgestrel administration].

Optical light microscopy was used in investigations of ovariectomised gravid gilts to which progesterone doses between 120 mg and 40 mg as well as 250 micrograms of oestradiol benzoate had been daily applied to preserve gravidity, with 12 mg of norgestrel being additionally administered to some of them. These investigations were conducted for the purpose of studying locally delimited effects of conception on the placental structure. Uterus tissue was sampled from living and dead embryos (centre and sides of ampullae) as well as from uterus regions free of foetal membranes (in-between ampullae). With adequate progesterone supply, embryos were shown to clearly affect the endometrial structures. Endometrium in the centre of ampullae, with living embryos, was lower than at points without embryos. Surface epithelium was flattened, and endometrial stroma was more strongly oedematised. Strongly pronounced hyperaemia occurred to subepithelial stroma in the centre of ampullae, and uterine glandular function was unambiguously stimulated. These embryo-triggered effects were much less or no longer detectable at all under conditions of inadequate progesterone supply (40 mg/die). Administration of 12 mg of norgestrel, in addition to 40 mg/die of progesterone, enabled embryos to exercise gravidity-specific influence upon the endometrium, as in cases of sufficient progesterone supply.