Factors influencing sperm-zona pellucida binding in vitro using the intact zona model

The zona pellucida binding assay assesses the ability of spermatozoa tobind to the zona pellucida. The present study investigated the influenceof: (i) prior oocyte exposure to spermatozoa on subsequent sperm-zonapellucida binding in vitro; and (ii) cryopreservation of oocytes. Onlyoocytes obtained from fertile donors were used and the binding capacity ofnon-inseminated, cryopreserved oocytes was compared with bothinseminated/unfertilized, cryopreserved oocytes andinseminated/unfertilized, non-cryopreserved oocytes recovered from in-vitro fertilization cultures on sperm-zona pellucida binding using anintact zona model. There was no statistically significant difference insperm-zona binding between non-inseminated, cryopreserved oocytes (range9.6-23.2), inseminated/unfertilized, cryopreserved oocytes (range15.0-16.0) and inseminated/ unfertilized, non-cryopreserved oocytes (range3.3-23.0). The coefficient of variation for sperm binding to all oocytegroups was very large (range 37-121%). We conclude that neither priorexposure of human oocytes to human spermatozoa nor cryopreservation ofhuman oocytes influences the subsequent binding of a different populationof spermatozoa to the zona pellucida. However, large oocyte-to-oocytevariation of sperm-zona binding may diminish the usefulness of this assayin clinical practice and as a research tool.