Assessment of quantitative dual-parameter flow cytometric analysis for the evaluation of testicular toxicity using cyclophosphamide- and ethinylestradiol-treated rats.

In the drug discovery process, effects to the human spermatogenesis must be fully evaluated before the first human trial. To estimate testicular toxicity, histopathological evaluation has been recommended in addition to the traditional mating procedure. However, it is laborious and time-consuming. Flow cytometric analysis (FCM) has also been applied to estimate testicular toxicity because of its speed, simplicity, and the objectivity of the data. Using cyclophosphamide (CP)- and ethinylestradiol (EE)-treated rat testis, we attempted to validate our dual-parameter, DNA ploidy and cell-size FCM, in a high-throughput toxicity study. Our results showed that CP damaged some spermatogonia and some early meiotic spermatocytes and EE caused severe decrease of spermatogenic cells except for spermatogonia as well as marked decrease of somatic cells, most probably Leydig cells. This is the first report discriminating between the changes of spermatogonia and that of somatic cells with FCM analysis. These results demonstrate that this method is a very useful and powerful tool to assess testicular toxicity, especially in high-throughput toxicological studies.