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 de rived fi om postmortem ovarian tissue were used for this study. Method s: Oocytes were randomly incubated either in synthetic human tubal flu id medium (untreated zonae) or in a chemically defined medium (treated zonae). Results: Sperm binding experiments using hemizona assay condi tions exhibited a 10-fold increased binding of sperm to treated compar ed to untreated oocytes (272.7 +/- 43 versus 24.3 +/- 15 sperm bound, respectively; P < 0.0001). pH recordings during incubation showed elev ated pH levels of 8.1 compared to pH 7.2 among treated and untreated z onae, respectively, Ultrastructural examination showed a spongy appear ance of the surface of treated zonae, whereas untreated zonae appeared compact with smooth surface. Conclusions: The marked increase in sper m binding among treated zonae, together with the ultrastructural findi ngs, suggest that the altered zona surface enhances sperm binding. The physiological maturational process of the zona pellucida might be man ipulated in vitro, thus increasing sperm binding to the zona.