Effect of heterologous seminal plasma on the fertilizing capacity of human spermatozoa as assessed by the zona-free hamster egg test

Abstract

The spermatozoa from 8 of 27 men showed a major increase (greater than 15%) in the oocyte penetration rate, the spermatozoa from 7 men showed a major decrease (less than 15%), and no major changes were noted in the other men when the spermatozoa were washed and preincubated with heterologous seminal plasma for 20 minutes before assessing their activity in the zona-free hamster egg assay. No difference was noted in motility or forward progression between the test and control spermatozoa. The increase or decrease in the oocyte penetration rate was consistent for all the ejaculates of a donor; i.e., a donor whose sperm showed an increase in the rate never showed a decrease, and vice versa. Additionally, the oocyte penetration rate of "epididymal-like" spermatozoa, obtained by ejaculation of the first fraction of a semen sample into a large volume of buffer, was enhanced when the spermatozoa were preincubated in their own seminal plasma, obtained from the other fraction of the ejaculate. It is concluded that seminal plasma can have a beneficial influence on the oocyte-penetrating capacity of spermatozoa that is independent of an effect on motility. However, the influence is probably often masked by the presence of antifertility factors in seminal plasma. The penetration-enhancing factor of seminal plasma has a molecular weight of less than 10,000, is quite heat-labile, but is stable at 4 degrees C. The penetration-enhancing factor is somewhat less stable at -20 degrees C and is unstable to lyophilization and reconstitution in H2O. Fertil Steril 40:512, 1983.