Potential indicators of reproductive toxicity: testicular sperm production and epididymal sperm number, transit time, and motility in Fischer 344 rats.

Comprehensive assessment of the effects of chemicals on male reproductive functioning requires study of effects on spermatogenesis and the quality of spermatozoa produced. As potential indicators of toxic effects, we have examined sperm production rate (SPR) and epididymal sperm numbers, transit time, and motility (percentage motile cells and swimming speeds) in Fischer-344 (F-344) rats. Groups (n = 14 or 15) of rats at 6, 8, 10, 15, and 20 weeks of age were studied to investigate the suitability of these indicators for detecting toxic effects, and to establish the age at which this strain of rat sexually matures. Mean SPRs (10(6) sperm/rat/day), as measured by enumerating spermatids in testicular homogenates, were 2 +/- 3, 22 +/- 6, 41 +/- 7, 49 +/- 6, and 46 +/- 7 at 6, 8, 10, 15, and 20 weeks, respectively. Epididymal sperm numbers and the percentage of motile spermatozoa also increased with age. No correlation was found between SPR and either testis weight or epididymal sperm number at 10, 15, or 20 weeks of age. Our results indicate that male F-344 rats become sexually mature between 10 and 15 weeks of age, and that testis weight and epididymal sperm number are unreliable quantitative indicators of sperm production rate. The low variability among adult rats in SPR and some of the other indicators of testicular and epididymal functioning examined in this study suggest that they should be sensitive measures of male reproductive toxicity.