Lysis of Oocytes by Bovine Sperm and Seminal Plasma

Abstract

This study examined the lytic activity of bovine seminal plasma on zona-free oocytes commonly used to assess bovine capacitanon. Exposure of hamster oocytes (intact or zona-free) to undiluted seminal plasma resulted in lysis within 5min. With intact oocytes, 1:5 to 1:20 seminal plasma resulted in swelling of the oocytes. With zona-free oocytes, seminal plasma (1:0 to 1:1000) resulted in lysis within 1min to 3h depending on dilution. Heating seminal plasma to inactivate complement did not reduce lytic activity, but boiling destroyed it. Lytic activity was present in seminal plasma from vasectomized bulls and in seminal vesicle fluid. After elution of seminal plasma through Sephadex G-200, lytic activity was only associated with the fraction containing proteins of 200,000 to 45,000 dal. Lytic activity remained with washed capacitated bull sperm only when 107 sperm/ml or more were coincubated with zona-free oocytes at 37°C for 3h. In conclusion, both bovine seminal plasma and capacitated sperm were lytic in the zona-free hamster oocyte assay. The results may explain why so few sperm are normally found at the site of fertilization.