The present study demonstrates the reproductive toxic and spermatotoxic effects of THP and DNB by conventional means (histology and DIC microcopy) and by novel approaches, including flow cytometric analysis of isolated epididymal spermatozoa and transcriptional profiling of select gene products within the proteolytic UPP. Our goal was to determine if transcriptional analysis and flow cytometry could capture minor changes in the male reproductive system of rats exposed to reprotoxic chemicals. We were particularly interested in examining threshold toxic exposures at which a conventional histological examination did not reveal any pathology.
No damage to testicular or epididymal tissues was identified by histology prior to Day 30 of THP exposure (Supplemental Table 1). Similarly, only some of the 2-mg/kg DNB-exposed animals showed testicular or epididymal histopathology (Supplemental Table 2).
Contrary to ambiguous histopathological findings, the THP-induced sperm damage and breakdown were manifested by altered flow cytometric median values of ubiquitin on Days 30 and 42 (Fig. 3). While the difference on Day 18 was not significant (P = 0.79), several treated samples already exhibited a flattened, shifted flow cytometry histogram, suggestive of sperm fragmentation, and a subpopulation of highly fluorescent cells, suggestive of increased sperm ubiquitination (see Fig. 3B).