Catalase-like and superoxide dismutase-like activities in human seminal plasma

Human spermatozoa are highly susceptible to oxidative injury but are naturally protected from such injury by the antioxidant properties of seminal plasma. We measured catalase-like and superoxide dismutase (SOD)-like activities in the seminal plasma of fertile and vasectomized men in order to gain insight into the potential source(s) and function(s) of these antioxidants in semen. Semen samples were obtained from fertile men ( n=11) and men post-vasectomy ( n=16). Catalase-like activity was measured by the decrease in hydrogen peroxide concentration after incubation with seminal plasma. SOD-like activity was measured as the inhibition of nitroblue tetrazolium reduction due to superoxide anion generation by xanthine plus xanthine oxidase. Mean seminal catalase-like activity (+/-1SD) in the fertile group was not significantly different from that of the post-vasectomy group (389+/-163 and 325+/-119 U/ml, respectively). Similarly, mean seminal SOD-like activity in the fertile group was not significantly different from that of the post-vasectomy group (37+/-10 and 36+/-10 U/ml, respectively). Our data suggest that the testis and epididymis are not an important source of catalase-like and SOD-like activities in semen. These findings indicate that antioxidants in semen are primarily of post-testicular origin and probably serve to protect ejaculated spermatozoa from oxidative stress such as that which occurs in the female reproductive tract.