Effects of castration on thiol status in rat spermatozoa and epididymal fluid

Mammalian spermatozoa gain their fertilizing ability as they mature in the epididymis, a process which is accompanied by oxidation of sperm protein thiols. Since sperm maturation is dependent upon normal androgenic support to the epididymis, the present work was designed to study the effects of castration on thiol status. Spermatozoa and epididymal fluid were isolated from the epididymides of male rats 5 days after castration or after 11 daily injections of the antiandrogen, cyproterone acetate. Spermatozoa and epididymal fluid were labeled with the fluorescent thiol labeling agent monobromobimane. Intact spermatozoa were evaluated by fluorescence microscopy, protein thiols were analyzed by electrophoresis, and fertilizing ability was examined after insemination of sperm suspension into the uterine horns of immature superovulated female rats. We found that both treatments resulted in an increase in cauda sperm thiols as shown by increased fluorescence in the intact spermatozoa. Protamines and nonbasic proteins were found to have increased levels of reactive thiols. The protein profiles of epididymal fluid from castrated rats were different from those of the controls, and the fluorescence patterns corresponded to the protein profiles. Our results indicate that testosterone withdrawal leads to inhibition of sperm thiol oxidation.