Origin of the human seminal plasma motility inhibitor within the reproductive tract

The origin of a human seminal-plasma sperm-motility inhibitor was investigated. Seminal vesicle and prostatic fluids, testes, epididymides, prostate and seminal vesicles were collected from young cadavers. The motility inhibitor, as measured by its capacity to block the motility of demembranated-reactivated sperm was present in significant amounts only in seminal vesicle fluid. The level of biological activity in this fluid was 13.6-fold higher than in seminal plasma. However, the concentration of motility inhibitor, as measured by ELISA, using an antibody generated against the motility inhibitor purified from human seminal plasma, was only 1.54-fold higher than in seminal plasma. The data suggest that the seminal plasma motility inhibitor originates from seminal vesicle fluid and that it is processed into a nine-fold less biologically active form when seminal vesicle fluid is mixed with other accessory gland secretions at ejaculation.