DOES THE ZONA-PELLUCIDA SELECT SPERMATOZOA FROM THE MEDIUM WITH HIGHER FERTILIZING POTENTIAL

The present study was carried out to test whether the zona pellucida s elects spermatozoa with higher fertilization potential. Fertilization rates of mouse oocytes after sperm microinjection under the zona pellu cida (SMUZ) of zona-bound spermatozoa and of spermatozoa incubated in the absence of oocytes and treated (acid-treated group) or not (contro l group) with acid Tyrode's solution were compared. SMUZ was performed at 15, 30, 60, and 90 min after the insemination of fresh oocytes req uired for selecting spermatozoa bound to the zona pellucida. At these- times, the percentages of acrosome-reacted spermatozoa (PARS) were eva luated using the chlortetracycline fluorescence method. Fertilization rate in the three groups analysed increased from 25.9% to 47.3% in the control group, from 29.3% to 44.0% in the acid-treated group, and fro m 19.5% to 40.0% in the zona-bound group from 15 to 90 min after insem ination, respectively. The global fertilization potential was signific antly lower in the zona-bound group compared to the other two groups. The PARS in the zona-bound group at 15 (11.48 +/- 3.02), 30 (16.74 +/- 3.71), and 90 (19.68 +/- 3.68) min after insemination were significan tly (P < 0.05) lower than those found in the acid-treated group (39.26 +/- 6.69, 38.20 +/- 6.24, and 42.83 +/- 5.39, respectively). At 90 mi n after insemination, the PARS in the zona-bound group was also signif icantly (P < 0.05) lower than the control group (36.72 +/- 4.51). No s ignificant correlation between either time and PARS or PARS and fertil ization rate was observed. It appears that the zona pellucida does not select from the medium spermatozoa with higher fertilization potentia l. (C) 1993 Wiley-Liss, Inc.