Histology discussion

Allopurinol has been shown to attenuate lipid peroxidation in ethanol-fed rats (Kato etal., 1990). However, this was not correlated with any possible effect on histological damage and, as discussed previously, the significance of lipid peroxidation is unclear. Despite the evidence suggesting that oxidative stress and increased oxidative metabolism may play a role in the pathogenesis of human alcoholic liver disease, it remains to be shown that treatment with specific antioxidants will modify this process. 

Histological changes in the spleen related to diisopropyl methylphosphonate intake were not observed in male or female rats exposed to 1 mg/kg/day of diisopropyl methylphosphonate in their drinking water for 26 weeks (Army 1978). As discussed in Section 2.2.2.1, there is some confusion concerning the concentration units and purity of the diisopropyl methylphosphonate used in the Army (1978) study (EPA 1989), and therefore results from the Army (1978) study are considered inappropriate for human health risk assessment. No changes in spleen weight were noted in male or female mink exposed to... 

Significant increases in serum urea nitrogen and serum creatinine levels (which may be indicative of impaired renal function) were observed in Pasteurella-infected rabbits exposed to 2,875 or 5,750 mg/kg/day of Fyrquel 220 for an intermediate duration (MacEwen and Vemot 1983). The results of the histological examination were not reported, and the renal effects of the infection were not discussed. 

As discussed in the previous section, long-standing inflammation may result in accumulation of iron in the reticuloendothelial system. In HIV-1 infection, a good example of a prolonged inflammatory process, such an excessive deposition of iron has been documented, and it may be responsible for an enhanced risk of certain infections (Boelaert etal., 1996). For instance, two studies reported an increased risk of Mycobacterium avium infection when such an excess of iron was present, as histologically documented (A1 Khafaie et ah, 1997 De Monye et ah, 1999). 

There are no studies in animals focusing specifically on the nervous system. In the lethality studies of Rowe et al. (1952) discussed in Section 2.2.1.1, rats and guinea pigs exposed by inhalation to higher concentrations of 1,2-dibromoethane had central nervous system depression (exact clinical signs not specified). Brain tissue apparently was not examined histologically. 

Liver was not examined histologically in the subchronic study used to set concentrations for the NCI chronic gavage bioassay of 1,2-dibromoethane (NC11978). In the NCI (1978) gavage bioassay (discussed in detail in Section 2.2.2.8), a nonneoplastic hepatic lesion, peliosis hepatis, occurred in a small number of treated male and female Osborne-Mendel rats and had an equivocal relationship to... 

A comprehensive histology evaluation was performed in this study, but the liver is the only tissue specifically mentioned as having been examined. Due to the total number of tissues examined (21) and route of exposure, it is probable that the gastrointestinal tract was examined but not discussed because no histopathologic changes were observed. 

While the risk that hormone replacement therapy may cause endometrial tumors has been widely discussed, less attention has been given to the possibility that it could increase the risk of epithelial ovarian cancer. Since cancer of the ovary has some risk factors in common with endometrial cancer (notably low parity and obesity), this possible risk needs to be considered, especially in view of the fact that the endometrioid epithelial type of ovarian tumor is histologically so similar to adenocarcinoma of the endometrium. 

Early dental caries (incipient lesions) are non-cavitated and limited to the outer enamel surface. Clinically, these lesions are identified as visible white spots when the tooth is air-dried (Fig. 11.1). The incipient lesion is known as a subsurface lesion since the surface appears intact. However, histological investigations have shown that below the surface, there are zones that vary in porosity (voids from mineral loss) as well as biochemical composition (e.g. fluoride, water and carbonate content) [29]. The enamel caries can vary from a depth of 100-250 J.m (for incipient caries) to entirely through the enamel ( 1.5mm deep), at which point the cavitated lesion has extended into the underlying dentin [35]. The diagnostic challenge remains early caries detection and the focus has been on caries lesions that form on the tooth crown affecting the enamel. The remainder of the discussion will therefore concentrate on enamel caries. 

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