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It has long been known that nicotine is metabolized to the corresponding amide cotinine (McKennis et al., 1957). The metabolism of nicotine has been investigated extensively (see Gorrod and Jenner, 1975; Nakayama, 1988). It has been suggested that the enzymatic formation of cotinine occurred via an intermediate (Hucker et al., 1960), which was then metabolized by “aldehyde” oxidase or “iminium oxidase” to form cotinine (Brandange and Lindblom, 1979; Hibberd and Gorrod, 1980). Evidence of a reactive intermediate probably from the cytochrome P-450 dependent oxidation of nicotine, was achieved when a stable product, identified as 5′-cyanonicotine was formed when cyanide was present during the metabolism (Murphy, 1973). This observation led Murphy (1973) to propose nicotine ∆l ′(5′) iminium ion as the reactive intermediate. To determine the site of enzyme activity responsible for the production of this reactive intermediate, experiments were carried out as in the original work by Hucker et al. (1960), and Booth and Boyland, (1971). Incorporation of radioactivity from 14C-cyanide by the substrate was examined by various cell fractions, i.e. isolated microsomes, and 140,000g soluble fraction. The metabolism of nicotine has been studied in many species. Miller and Larson, (1953) observed its metabolism by tissue slices from mouse, rabbit, rat, and dog. Enzymic oxidation of nicotine has also been observed in guinea pig (Booth and Boyland, 1971), and rabbit (Hucker et al., 1960). It was therefore decided to investigate the in vitro metabolism of nicotine to the cyanonicotine adduct by different mammalian laboratory species. |
