THE EFFECT OF PARTIAL ZONA DISSECTION ON THE FERTILIZING-CAPACITY OF CHRONICALLY OBSTRUCTED MOUSE CAPUT EPIDIDYMAL SPERM

Purpose: Having observed that sperm from the chronically obstructed ca put epididymis fertilize poorly in vitro, we investigated the effect o f partial zona dissection (PZD) on fertilization in a murine model of unilateral proximal epididymal obstruction. Cleavage rates were compar ed for zona-intact oocytes and PZD oocytes incubated with sperm from t he following epididymal segments: the obstructed caput, the contralate ral nonobstructed caput, the contralateral cauda, and a sperm-free pre paration to control for parthenogenesis. Results: Unilateral epididyma l obstruction resulted in significantly higher sperm counts in the obs tructed caput compared to the nonobstructed caput, although there was no difference in motility. Cleavage rates for ova incubated with sperm from the obstructed caput and the nonobstructed caput were uniformly poor and did not differ significantly from those for the sperm-free co ntrols. Cauda sperm fertilized significantly better than all other spe rm groups (P < 0.05). Partial zona dissection did not improve cleavage rates in any group. Conclusion. We conclude that sperm from the chron ically obstructed caput epididymis, like sperm from the normal caput, are unable to fertilize ova, and PZD does not enhance this poor fertil izing capacity. Furthermore, the finding that PZD does not improve the fertilizing capacity of the presumably mature cauda sperm in our mous e model suggests that any beneficial effect of PZD may be strain-speci fic.