Human sperm penetration into zona-free hamster oocytes as a test to evaluate the sperm fertilizing ability

Human sperm entry into zona-free hamster oocytes was used to test the fertile ability of spermatozoa from semen samples of men attending an Infertility Clinic. Sperm chromatin dispersion as seen under the phase-contrast microscope, was used as criterion for sperm entry. The ultrastructural study showed that the behaviour of the gamete membranes during fusion did not basically differ from that of normal fertilization. Eighty four samples were classed as normal (according to the spermiogram) but only 62 (74%) gave a positive test, as compared to only 30 (32%) positive test of 95 samples with abnormal spermiograms. Eight hundred and ten oocytes inseminated with spermatozoa from normal samples gave a 25% penetration, while 1046 oocytes inseminated with spermatozoa from abnormal samples gave a 7% penetration. The normality of hamster oocytes was demonstrated by contemporary insemination with human and hamster spermatozoa. While the percentages of human sperm penetration remained low, hamster sperm penetration was over 70%. The present bioassay is recommended as an additional parameter to the spermiograms for the study of male fertility.