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  • Title: N-methylation as a toxication route for xenobiotics. II. In vivo formation of N,N'-dimethyl-4,4'-bipyridyl ion (paraquat) from 4,4'-bipyridyl in the guinea pig.
    Author: Godin CS, Crooks PA.
    Journal: Drug Metab Dispos; 1989; 17(2):180-5. PubMed ID: 2565208.
    Abstract:
    The biotransformation of 4-phenylpyridine and 4,4'-bipyridyl to N-methylated quaternary ammonium metabolites in guinea pig and rabbit has been examined. Neither animal species excreted the neurotoxin N-methyl-4-phenylpyridinium ion as a urinary metabolite after ip administration of 4-phenylpyridine. However, treatment of rabbits with 4,4'-bipyridyl resulted in the formation of N-methyl-4,4'-bipyridinium ion in the urine (1.2% of the administered dose), and ip administration of 4,4'-bipyridyl to guinea pigs afforded both N-methyl-4,4'-bipyridinium ion and N,N'-dimethyl-4,4'-bipyridinium ion (paraquat) as urinary metabolites (0.8% and 2.9%, respectively, of the administered dose). The detection of the lung toxin paraquat as a urinary metabolite of 4,4'-bipyridyl is a significant finding, in that it represents the first documented report of the formation of a toxic metabolite via the N-methylation pathway.
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