Critical aspects of histopathological evaluation

Identifying the histopathologic consequences of severe endocrine disruption in the male reproductive system is not difficult. Marked changes in organ weights of the various tissues are accompanied by significant morphologic changes in the same tissues. Detection of weak endocrine disrupting activity is much more difficult because the weight changes, and more importantly the histopathologic changes, are much more subtle and require the pathologist to have a detailed knowledge of spermatogenesis as well as the cell and stage specific changes that are characteristically associated with hormonal perturbation in the reproductive system. The more subtle the changes, the more important it is to have ideal fixation, consistent trimming of tissues and an excellent knowledge of the background variation of the normal structure and function of the tissues being examined. The TG407 protocol utilizes only 5 animals/sex/group and so weak endocrine disruptors may produce subtle changes in only a proportion of those few animals; this makes overinterpretation of findings a real risk. The following points are provided to aid the investigator in deciding what is “within normal range” and what the most sensitive indicators of endocrine disruption are. Microscopic Finding Sensitivity of the finding as an endpoint of endocrine disruption Variability in normal animals Testes Spermatid retention One of the earliest and most sensitive indicators of low intratesticular testosterone, but may also be seen with other mechanisms of testicular toxicity. Needs to be interpreted in conjunction with other endpoints. Occasionally seen in control testes at the lumen of stage IX-XI tubules. Stage XII tubules may have 1-3 retained spermatids in basal cytoplasm. Stage VII/VIII degeneration of round spermatids and pachytene spermatocytes Very specific and sensitive marker of low intratesticular testosterone. Only a few cells may be affected in any given tubular profile, but the celland stage-specificity is critical and highly diagnostic Not generally seen as a background finding in control animals.