Effect of early ovariectomy and steroid hormone replacement of embryo transport, development and implantation in mice.

Bilateral ovariectomy on Day 1 of pregnancy increased abnormal embryo numbers on Day 4 and delayed passage of embryos to the uterus. Progestins given on Day 1 reversed these effects; given on Day 3 they reduced numbers of abnormal embryos, but did not restore normal transport. Oestrogen given alone after ovariectomy increased embryo loss, but restored preimplantation embryo development to normal when given on Day 3 after progestins on Day 1. The results suggested that both oestrogen and progesterone were necessary for normal preimplantation embryo development in vivo. However, although Day-1 progestins produced the greatest improvement in embryo transport and preimplantation development, they supported only low implantation rates compared with progestins starting on Day 3, and no progestin treatment returned implantation rates to normal. Sham ovariectomy on Day 1 also reduced implantation rate, suggesting that surgical stress of Day-1 ovariectomy had major adverse effects on embryo viability. This view was supported by experiments involving unilateral ovariectomy, which produced abnormalities in embryo transport, development and implantation, but only on the operated side. Furthermore, the major abnormality induced in embryo development by unilateral and bilateral ovariectomy, viz embryonic autolysis, was not increased in experiments in which pregnancy was blocked by non-surgical antagonism of progesterone. It is concluded that abnormalities in embryo development induced by early ovariectomy are not caused by a deficit of endogenous hormones, but result largely from effects of surgical trauma on oviduct function which can be reversed by treatment with exogenous hormones.