ENDOCRINE AND ENDOMETRIAL SECRETORY PROTEIN-CHANGES ASSOCIATED WITH UTERINE RECEPTIVITY IN SHEEP

Crossbred ovariectomized ewes were treated with steroid therapies dete rmined previously to be adequate (progesterone-primed) or inadequate ( unprimed) for embryonic development in order to determine actual serum concentrations of replaced steroid hormones achieved by such treatmen ts and to identify secreted endometrial proteins that might mediate ut erine receptivity. Ewes received estradiol-17-beta on day 0, and on da ys 1-4, either vehicle (unprimed; N=16) or progesterone (primed; N=16) daily. All ewes then received ''estrus estradiol'' (at 8 hr-intervals ), followed by ''maintenance progesterone'' (at 12 hr-intervals), to m imic endocrine profiles of intact ewes at and following estrus. Jugula r blood samples were obtained at 4-hr intervals from 6 ewes/treatment on day 0-15 to determine serum progesterone, estradiol, and PGFM conce ntrations. Endometrium from two ewes/treatment on days 11-15 was cultu red in vitro with [H-3]leucine and radiolabeled proteins in media were analyzed electrophoretically. Results demonstrated that 1) treatments generated transient serum estradiol levels slightly greater than thos e reported in intact animals at estrus, 2) serum progesterone concentr ations due to treatments were similar to those reported in the luteal phase of intact ewes, 3) progesterone-priming was specifically associa ted with a small, sustained (24-36 hr) elevation in serum PGFM, and th at 4) priming was not associated with the presence or absence of major , secreted endometrial proteins that might act either as factors requi red for development or as embryotoxins. These results suggest that pos itive effects of progesterone-priming on embryo survival are not due t o pharmacological doses of exogenously administered hormones, nor are due to changes in secretion of hormonally-regulated, major endometrial proteins.