Origin and distribution of potassium bromate-induced testicular and peritoneal mesotheliomas in rats

Tissue sections were examined from a 2-year bioassay of male Fischer 334 ra ts treated with potassium bromate administered in drinking water. All anima ls exhibiting peritoneal mesotheliomas also had mesotheliomas of the tunica vaginalis testis mesorchium (the reverse was not true), and the correlatio n of these 2 types of mesotheliomas was highly significant (r(2) = 0.98). M apping of the tunica vaginalis tumors at all time points and at all bromate concentrations revealed a pattern of increasing incidence of tumor formati on on the mesothelium of the tunica vaginalis testis as a function of proxi mity to the mesorchial ligament. Thus, the mesorchium appears to be the maj or mesothelial target site for potassium bromate-mediated carcinogenesis. T he frequency of occurrence of mesotheliomas by location was tunica vaginali s testis (25%), mesosplenium (20%), mesentry (10%), mesojejunum/mesocolon ( 8%), bladder (6.5%), mesogastrium (13%), liver serosa (5%), and kidney, sma ll intestine, and rectum (1% each). A complete cross-section of the rat tes tis was prepared and used I:to construct a complete map of the mesothelium. Any attempt to determine the role of local dose and tissue susceptibility for the purpose of interspecies risk extrapolation must take into account t he complex anatomy and physiology of this region of the visceral and testic ular suspensory apparatus. Improved histologic approaches are needed for ad equate assessment of this delicate suspensory system.