The cortical reaction in pig oocytes during in vivo and in vitro fertilization

The structure of pig oocytes after in vivo and in vitro fertilization and following treatment with the ionophore A23187 with differing levels of calcium are described, with particular reference to the cortical granules. Fertilization in vivo and in vitro resulted in cortical granule exocytosis. Sperm penetration in vivo was more rapid than in vitro and resulted in the dispersal of the cortical granules' contents in the perivitelline space following exocytosis. The contents of the granules remained adjacent to the plasmalemma after in vitro fertilization and suboolemmar vesicles were less numerous than after in vivo fertilization. High calcium levels were necessary to induce the dispersal of the cortical granule contents following treatment with ionophore. The observations are discussed regarding their relevance to the blockage to polyspermy.