Uterine luminal proteins at the time of implantation in rats

Changes in rat urerine luminal proteins were analysed during pregnancy and after ovariectomy on Day 3 of pregnancy plus daily administration of progesterone, when delay of implantation is imposed. Total protein levels reached a peak level on Day 5 of pregnancy, the day of implantation, in the intact but not the ovariectomized females. Qualitative analyses of protein-SDS complexes showed an increase in a protein of molecular weight of approximately 70.000 and others of higher molecular weight during pregnancy, but in ovariectomized females the proteins of higher molecular weight were virtually undetectable by Day 10. The entry of blastocysts into quiescence after ovariectomy appears to be an adaptation by the embryos to suboptimal uterine luminal conditions.