These results suggest that FCS also inhibits cortical and/or zona reactions in bovine oocytes. In the present study, we used BSA, not FCS, in our culture and fertilization media, and these conditions can produce embryos that are more viable by preventing polyspermic penetration. It is possible that these media induce more normal cortical and zona reactions than do other media that have been used in pig IVF Further, during normal fertilization (in the oviduct), sperm heads were observed only in the ZP, not in the PVS, suggesting that pig oocytes have a strong zona block to polyspermic penetration under physiological conditions. Although the reasons for high polyspermy with pig IVF are not completely understood, it is suggested that oviductal secretions may participate in the prevention of polyspermy. In our IVF studies, sperm begin to penetrate oocytes 3 h after insemination. Therefore, it is possible that by 3 h after A23187 treatment, a sufficient cortical reaction has occurred to induce a zona and/or PVS block, although the actual time was not determined. It has been reported that the zona reaction requires 17-35 min in the hamster, 60-120 min in the mouse, and 10-100 min in the rat. Further experiments are necessary to examine the zona reaction time of pig oocytes during fertilization. Recently, we also found that there were major differences between the extracellular matrices (ZP and PVS) of pig oocytes matured in vitro and those flushed from oviducts. The changes in the extracellular matrix may participate in the block to polyspermic penetration by an as yet unknown mechanism. buy asthma inhalers
In conclusion, the present study indicates that A23187-induced activation of pig oocytes is positively correlated to the ability of A23187 to induce a Ca2+ transient, and also provides the experimental evidence that [Ca2+], changes play an important role(s) in oocyte activation. The Ca2+ transients that follow oocyte activation induced by A23187 are concentration-dependent. In addition, the A23187-in-duced cortical reaction can establish a block to sperm penetration, indicating that the cortical reaction and modification^) in the ZP and/or PVS by CG materials in pig oocytes are functional. A determination of cortical and zona reaction time during oocyte activation is needed to investigate further cause(s) of polyspermy in pig oocytes after IVF.