A 250 kDa secretory protein was isolated from the uterine luminal fluid (ULF) obtained from estradiol-treated ovariectomized rats. Antiestrogens blocked the production of this protein. The protein components were separated and purified by SDS-PAGE. Polyclonal antibodies were raised against the 250 kDa protein and used to identify the protein by Western blot. 17 beta-estradiol (E2) at a dose of 0.005 mg/kg/d administered s.c. for 3 days to ovariectomized rats stimulated a marked increase in the production of the 250 kDa protein. Anordiol at a low dose of 5 mg/kg/d x 3 p.o. or 0.25 mg/kg/d x 3 s.c. stimulated the production of the 250 kDa protein. Treatment with higher doses (10 mg/kg/d x 3 p.o., or 1.25 mg/kg/d x 3 s.c.) was less effective in inducing production of this protein. Also anordiol partially inhibited the stimulatory action of E2; whereas ICI 182,780, a pure antiestrogen, at a dose of 0.3 mg/kg/d x 3 s.c. completely blocked the stimulatory action of E2. The 250 kDa protein was not detected in the blood obtained from E2-treated ovariectomized rats. The anti-complement C3 and anti-alpha 2-macroglobulin antibodies did not react with the ULF 250 kDa protein. The present results show that the production of the ULF 250 kDa protein is regulated by estradiol and is not a component of blood plasma. It is proposed that the estrogen-responsive 250 kDa protein may be involved in maintaining the viability of the fertilized ova and in the implantation of the blastocyst.
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