The presence of zonae pellucidae influences fusion rates between spermatozoa and zona free hamster oocytes.

Human zonae pellucidae were added to suspensions of capacitating spermatozoa. The zonae were prepared from oocytes that remained unfertilized in our in-vitro fertilization (IVF) programme. After capacitation, zona free hamster oocytes were added and the penetration rate of the hamster oocytes was determined. Controls without the addition of zonae were run in parallel. A distinct enhancement of the penetration rate was found when zonae were present during capacitation, using sperm of fertile donors. Sperm of several infertile men did not respond to the presence of zonae with higher penetration rates. It was concluded that the zona pellucida is involved in the induction of the acrosome-reaction of human spermatozoa. In addition the incubation system with zonae as described might be useful for the identification of infertile semen.