Disruption of cellular associations within the granulosal compartment of periovulatory ovine follicles: relationship to maturation of the oocyte and regulation by prostaglandins.

Temporal relationships were defined in sheep between the onset of the preovulatory surge of luteinizing hormone (LH; 0 h), dispersion of mural granulosal cells and cumulus oophorus, resumption of meiosis of the oocyte, and ovulation. A quantitative increase in intercellular spacing among mural granulosal and cumulus cells was detected at the light-microscopic level 12 h following the onset of the surge of LH. Evidence of breakdown of the germinal vesicle of oocytes was apparent at 16 h and thereafter. Ovulation occurred near 24 h. Systemic administration of indomethacin, an inhibitor of prostaglandin/PG biosynthesis, at 8 h subsequently prevented dissociation of mural granulosal and cumulus cells and suppressed maturation of the oocyte. The action of the drug was reversed by intrafollicular injection of PGE2 at 12 h; PGF2 alpha was ineffective in this regard. Prostaglandin E2 appears to be involved in preovulatory ovine follicles in the dissolution of cell-to-cell contacts and in maturation of the oocyte.