Effects of plasmin on sperm-oocyte interactions during in vitro fertilization in the pig

The present study was undertaken to examine the effect of plasmin on sperm viability and sperm-oocyte interaction during in vitro fertilization in the pig. Porcine sperm, which were washed in Dulbecco's PBS were re-suspended and incubated in fertilization medium (mTBM; modified Tris-buffered medium) containing 0, 0.1, 1.0, 10.0 or 100.0ng/mL of plasmin. Sperm viability was not affected by plasmin treatment. Addition of plasmin in doses ranging from 0.1 to 100.0ng/mL for 2, 4 or 6h to washed boar sperm resulted in enhancement of acrosome reaction (AR) compared with untreated cells. The concentration of 0.1ng/mL plasmin (95+/-18 sperm/oocyte) had no effect on sperm binding, whereas 1.0ng/mL (123+/-21 sperm/oocyte), 10.0ng/mL (124+/-16 sperm/oocyte) and 100.0ng/mL (124+/-15 sperm/oocyte) of plasmin increased sperm binding compared with the control (83+/-15 sperm/oocyte). The zona pellucida solubility (zona dissolution time) was less in medium with 1.0ng/mL (123+/-24s), 10.0ng/mL (99+/-15s) or 100.0ng/mL (95+/-19s) plasmin compared with control (176+/-27s). When pig oocytes and sperm were co-incubated in various concentrations of plasmin for 6h, the penetration rate was greater in medium with 1.0ng/mL plasmin (77.5+/-3.1%) compared with the control. However, there were no differences in the polyspermic rates and mean number of sperm (MNS)/oocyte between the groups treated with plasmin and control. These results suggest that plasmin might play a role in events related to fertilization.