Influence of elevated pH levels on structural and functional characteristics of the human zona pellucida: functional morphological aspects.

PURPOSE

A total of 86 fresh and salt-stored immature human oocytes derived from postmortem ovarian tissue were used for this study.

METHODS

Oocytes were randomly incubated either in synthetic human tubal fluid medium (untreated zonae) or in a chemically defined medium (treated zonae).

RESULTS

Sperm binding experiments using hemizona assay conditions exhibited a 10-fold increased binding of sperm to treated compared to untreated oocytes (272.7 +/- 43 versus 24.3 +/- 15 sperm bound, respectively; P < 0.0001). pH recordings during incubation showed elevated pH levels of 8.1 compared to pH 7.2 among treated and untreated zonae, respectively. Ultrastructural examination showed a spongy appearance of the surface of treated zonae, whereas untreated zonae appeared compact with smooth surface.

CONCLUSIONS

The marked increase in sperm binding among treated zonae, together with the ultrastructural findings, suggest that the altered zona surface enhances sperm binding. The physiological maturational process of the zona pellucida might be manipulated in vitro, thus increasing sperm binding to the zona.