Origin of a motility inhibitor within the male reproductive tract

Seminal plasma contains a motility inhibitor of demembranated reactivated spermatozoa. We investigated its origin within the reproductive tract. The highest level of inhibitor was detected in seminal vesicle fluids from the three species investigated (bull, rat, rabbit). Significant levels of inhibitor were also observed in prostatic fluids. Testes and epididymal fluids, as well as bulbo-urethral and coagulating gland homogenates were essentially devoid of inhibitor. On a mg protein basis, the inhibitor in seminal vesicle fluid was about four times less active than the inhibitor of seminal plasma. The high level of inhibitor in seminal plasma can not be explained by the synergistic effect of the combination of seminal vesicle, prostatic and epididymal fluids. Dialysis experiments suggested that the high level of inhibitor in seminal plasma was mainly due to the presence of a dialysable activator. This activator is capable of potentiating up to four-fold the inhibitor present in seminal vesicle fluid.