A HIGH-MOLECULAR-WEIGHT PREOVULATORY STAGE-RELATED PROTEIN IN EQUINE FOLLICULAR-FLUID AND GRANULOSA-CELLS

The high-molecular-weight proteins of equine follicular fluid were exa mined to determine whether some polypeptides are unique to certain phy siological conditions. Fluids from ovarian follicles of various diamet ers and physiological stages during the follicular phase were recovere d by ultrasound-guided follicular aspiration. Granulosa cells and cumu lus-oocyte complexes (COG) were recovered by scraping the intrafollicu lar wall during puncture. Follicular fluids and corresponding serum, a s well as granulosa cell lysates, were analyzed by one-dimensional SDS -PAGE and silver staining. COC morphology was assessed microscopically . A 200-kDa protein band was demonstrated in fluids from preovulatory follicles, in natural conditions or after induction of ovulation. This protein band was absent in fluids from follicles at earlier stages, s ubordinate follicles, and serum. The presence of this protein at the p reovulatory (PO) stage was ascertained through recovery of the fluid f rom follicles twice during their growth. Its appearance was time depen dent after induction of ovulation but was not induced by an intrafolli cular injection of a physiological dose of progesterone. We also demon strated the presence of this 200-kDa protein in granulosa cells lysate s recovered from preovulatory follicles. The expression of this protei n in the follicular fluid was related to the cumulus aspect and chroma tin configuration of the enclosed COG. No relation was found between i ts presence in the follicular fluid at the PO stage and subsequent ovu lation of the punctured follicle or embryo production. The identificat ion of this molecule is approached and discussed. These results show a novel PO stage-related protein in equine follicular fluid, which may be involved in the differentiation and maturation mechanisms occurring in the follicle during the preovulatory period.