Although there was no evidence to suggest that increased zona binding in itself resulted in enhanced instability, the concomitance of the zona binding changes and of cell death in response to IVF conditions was in accord with the general concept of capacitation as a destabilizing process.
As well as noting the heterogeneity of response within a sperm population, we also noted considerable variation between ejaculates. A particular point of interest is that sperm in the ejaculates described above, taken from boars in the Babraham Institute colony, showed attenuated but perceptible increases in sZP binding during incubation in the absence of bicarbonate. However, in later experiments on ejaculates from boars at a Dutch Al station, the percentage of live sperm with increased zona binding capacity barely rose at all during incubation in the absence of bicarbonate, remaining on average below 10% (46 ejaculates of 18 boars, manuscript in preparation). Given the biphasic nature of the overall response, the question arises as to whether the cells that undergo rapid changes represent the competent population or whether a slow population response is more desirable (better survival in vivo?). Regardless of the answer, such variations in development of what we consider to be a physiologically relevant characteristic suggest that acquisition of zona binding ability under IVF conditions might be a useful parameter for assessing the fertilizing ability of boar semen samples. flovent inhaler