Physiological roles of estrogen and TGF-α in the maintenance of pregnancy

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Pregnancy and its maintenance are essential for reproduction of farm animals. This study was performed to clarify the physiological roles of estrogen and TGF-α in pregnancy, and the final objective is to contribute towards the increase of pregnancy rates in farm animals.Continuous treatment with an inhibitor of estrogen. production, fadrozole hydrochloride (Fad), during early pregnancy delayed preimplantation embryo development, zona shedding by embryos and the period of maximum sensitivity to a decidualizing stimulus in rats. Since the treatment delayed the initiation of implantation by 1 or 2 days, it was speculated that estrogen might stimulate the embryo development and prepare the uterus for implantation. Continuous treatment with Fad during late pregnancy reduced the concentration of plasma estrogen and increased the uterine mRNA expression of lysyl oxidase (LO), which is necessary for the formation of intra-and inter-molecular cross-links of collagen. The treatment reduced the s … More ize and compliance of the uterine tissue framework and increased the intrauterine pressure by 4-fold to cause injuries in about one-quarter of fetuses. These results suggest that estrogen inhibits uterine expression of LO and keeps the physical environment suitable for the rapidly growing fetuses in late pregnancy. On the other hand, expression of TGF-α and its receptor (EGF-R) in the embryo and endometrium was found in the ovine implantation process, and it was speculated that TGF-α might stimulate the embryo growth and regulate proliferation and differentiation of endometrial cells. Furthermore, expression of TGF-α and EGF-R was observed in the canine endometrium, and the possibility of their involvement in the proliferation, differentiation and regression of endometrial epithelial cells was suggested.In conclusion, estrogen enhances the embryo growth and regulates the proliferation, difforentiation and regression of endometrial cells, resulting in establishment of implantation. Estrogen also regulates uterine expression of LO and keeps the uterine physical states suitable for fatal growth. Furthermore, TGF-α expressed in the uterus may play important roles in the embryo growth and the proliferation, differentiation and regression of endometrial cells. Less