This study was conducted to investigate the effect of plasmin and heparin on in vitro ovine spermoocyte interaction. Different concentrations of plasmin (0, 1, 10, 100 ng/ml) and heparin (0, 5, 10 IU/ml) were added alone or simultaneously into fertilization medium. After sperm and oocyte co-culture, binding and penetration of sperm to zona pellucida (ZP) were assayed. Treatment with 1 and 10 ng/ml plasmin resulted in higher sperm binding to ZP than those in control. The rates of sperm binding to ZP were increased with highest heparin concentrations (10 IU/ml). Heparin had no effect on penetration rate of sperm to ZP. Simultaneously effects of plasmin and heparin were not significant on penetration rate of sperm to ZP. But, 5 or 10 IU/ml heparin in the present of 1 ng/ml plasmin had higher effect on sperm binding to ZP than that in the other groups. These results suggest that plasmin and heparin (alone/simultaneously) might play a role in events related to fertilization in ovine
