Enzymatic metabolism, xenobiotics mammals

The principal pathway by which unsubstituted and many substituted aromatic hydrocarbons are metabolized in mammals consists of the initial formation of arene oxides, which undergo a variety of enzymatic and nonenzymatic reactions prior to excretion of the resulting more polar, oxidized hydrocarbons via bile or urine. Taken together, these pathways represent an attempt on the part of the animal to detoxify or eliminate such nonpolar xenobiotic substances for which it has no apparent use. Although detoxification is the probable role of the arene oxide pathway, it is equally clear that chemically reactive species mediate this process. Thus, studies over the past several years have either implicated or established arene oxides in a causative role in such adverse biological reactions as cytotoxicity, mutagenesis, and carcinogenesis via covalent interaction of arene oxides with biopolymers,... 

Xenobiotic GSH conjugates are metabolically unstable in higher plants and rapidly undergo additional enzymatic and/or nonenzymatic transformations to a variety of products by processes that have been reviewed recently (15,26, ). With several exceptions, the primary routes of metabolism of GSH conjugates in plants are similar to those observed in mammals as discussed by Baldce in Chapter I6. In sorghum and corn, the first step in the catabolism of a xenobiotic... 

Unlike mammals, fish do not appear to exhibit a defined relationship between portal spaces and terminal hepatic venules. This apparent lack of organization also has been reported on the biochemical level. Enzymatically, heterogenous zones of hepatocytes as found in mammals are not evident in fish (35,36). In addition hepatic perfusion is poor in fish with rates 1/2 to 1/4 of those found in mammals. These features may be important in regards to metabolism and toxicity of xenobiotics. 

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