Short-term male reproductive toxicity study with sulfasalazine in the rat.

Sulfasalazine (2-hydroxy-5-[[4-[(2-pyridinylamino) sulfonyl] phenyl]azo]benzoic acid; SASP) was administered to rats in a short-term male reproductive toxicity study to further examine the utility of this grouping of techniques and to generate reference data with a substance that is known to cause reversible infertility in men. Adult male CD rats (10/group) were orally administered 0, 150, 300, or 600 mg SASP/kg body weight in divided doses for 14 d followed by a 2-week period without treatment. Males were killed on test day (TD) 15 or 29. At each time point, the reproductive system was evaluated by comparing testicular and epididymal weights, DNA ploidy distributions of testicular cell suspensions, testicular and epididymal histopathology, and epididymal sperm concentrations, motion, morphology, and breakage. Adding time as a factor in the protocol aids in distinguishing testicular from posttesticular effects. Changes in sperm quality after 2 weeks of test article administration (TD 15) predominantly reflect effects that occurred after the sperm entered the epididymis, while testicular effects predominated on TD 29. Beginning on TD 14, males to be killed on TD 29 were cohabited with untreated females (1:2). Females were killed at midgestation and examined for pregnancy status. Body weight gain was depressed in all SASP groups during the first 3 d of test article administration. Food consumption was depressed at the 300- and 600-mg/kg dose levels. No changes were seen in testicular weight, but epididymal weight was depressed at the 600-mg/kg dose level. DNA ploidy distributions determined by flow cytometry did not indicate that the kinetics of spermatogenesis were disturbed. However, alterations in sperm release, which have not previously been reported, were seen at all SASP dose levels. On TD 29, the percentage of progressively motile sperm was depressed and beat/cross frequency was increased at the 600-mg/kg dose level. No changes were observed in sperm morphology or breakage. Fertility was slightly depressed at the 600-mg/kg dose level. In this study, testicular histopathology provided the most sensitive endpoint for reproductive toxicity. The impairment of fertility immediately after treatment was stopped, when no changes were apparent in sperm release or sperm motion, suggested that decreased sperm concentrations and altered motility, while contributory, may not be the primary causes of SASP-mediated infertility.