Effects of the male antifertility agent ornidazole on sperm function in vitro and in the female genital tract.

Infertility is induced in male rats by oral administration of 400 mg ornidazole kg-1 body mass day-1 within 10 days, without drastic effect on the motility of epididymal spermatozoa obtained after 15 days of treatment. Spermatozoa were recovered from the female tract 9 h after mating with males treated with ornidazole for 10 days to identify the cause of infertility. The number and motility of spermatozoa in the uterus indicated normal seminal deposition. Spermatozoa could pass the utero-tubal junction but total numbers of spermatozoa and their velocities in the oviductal isthmus were significantly lower than those recovered from females mated to fertile, control males fed vehicle alone. However, the number of spermatozoa recovered from the ampulla was not different from control and the number of spermatozoa that had penetrated the cumulus mass was lower and none of the eggs was fertilized by spermatozoa from rats treated with ornidazole. The ability of cauda epididymal spermatozoa from ornidazole-fed rats to penetrate viscous media in vitro was lower than that of the controls. When incubated in media containing different concentrations of substrates and ions, a reduction in movement of spermatozoa was observed when glucose was the only exogenous substrate or after preincubation in substrate-free medium. These results indicate that the antifertility action of orally administered ornidazole occurs via damage to spermatozoa in the upper regions of the female tract, possibly reflecting a failure in capacitation as a result of reduced energy production.