Metabolism and testicular toxicity of 1,3-dinitrobenzene in rats of different ages.

Susceptibility to 1,3-dinitrobenzene (1,3-DNB)-induced testicular damage is known to increase with age. The present study investigated the possibility that age-dependent differences in metabolism and disposition could account for differences in toxicity. [14C]1,3-DNB (25 mg/kg, ip) was administered to Sprague-Dawley rats which were 31, 75, or 120 days of age. Levels of 1,3-DNB and 1,3-DNB metabolites were determined in blood and urine. As animal age increased, peak blood concentrations of 1,3-DNB were lower and declined more slowly indicating an age-dependent decrease in rate of metabolism and a possible increase in volume of distribution. In younger animals, faster elimination rates were associated with higher blood levels of metabolites. Urinary metabolites were generally similar for all age groups with the exception of the diacetamidobenzene metabolite which was significantly lower in the urine of 31 days old rats. There were clear differences in the toxicokinetic profile for 1,3-DNB between the 31 day old rats and the other two age groups. However, differences between the 75 and 120 day old animals were less marked. Testicular damage induced by 1,3-DNB (25 mg/kg, ip) was hardly detectable in the youngest animals, while the intermediate age group showed a moderate lesion particularly in later stages of spermatogenesis. For the oldest animals, testicular damage was more severe, particularly in the earlier stages of spermatogenesis. Overall, the rapid elimination rate could account for the lack of 1,3-DNB toxicity in very young animals. However, simple metabolic differences were less likely to adequately explain the increase in testicular damage found as animal age increased from 75 to 120 days.