1. The metabolism of [2,6-14C]pyridine in vivo has been investigated in the rat, hamster, mouse, gerbil, rabbit, guinea-pig, cat and man, and the quantitative determination of the various urinary metabolites carried out by radiochromatographic analysis. 2. Unchanged pyridine and its N-methylated metabolite, N-methylpyridinium ion, were determined using a Partisil-10 SCX cation-exchange h.p.l.c. column, whereas the C- and N-oxidation products were assayed by reverse-phase chromatography, using a Partisil-10 ODS column. 3. Most of the species studied produce pyridine N-oxide, N-methylpyridinium ion, 2-pyridone, 3-hydroxypyridine and 4-pyridone as metabolites, but the proportion of the dose excreted as each of these metabolites is species-dependent.
A new titrimetric method is described for determining certain sulphonamides. The proposed method is based on the fact that N-bromosuccinimide readily and quantitatively brominates an aqueous acidic solution of the sulphonamide and is itself irreversibly reduced to succinimide. The mechanism of the reaction is illustrated. The experimental error is within 5 1 per cent.CEKTAIS sulphonamides, such as sulphanilamide, sulphaguanidine and sulphacet amide, cannot be determined by the silver nitrate meth0d.l Further, sulphanilamide and sulphaguanidine cannot be estimated by the recent complexometric method,2 whose error in case of sulphacetamide sodium amounts to more than 20 per cent.This paper describes a new method for determining these sulphonamides. The proposed method is based on the fact that N-bromosuccinimide readily and quantitatively brominates an aqueous acidic solution of sulphanilamide, sulphaguanidine or sulphacetamide to the corresponding 3,5-dibromo derivative and is itself irreversibly reduced to succinimide, as repreGnted 6v the equation-CHZ-CO, >NBr + H,NH-~SO,-NH.R 2 C I_ HZ-CO'
IN the presence of dilute hydrochloric acid, N-bromosuccinimide readily and quantitatively oxidises aqueous solutions of isoniazid. The reaction takes place a t room temperature and N-bromosuccinimide is irreversibly reduced to succinimide. The mechanism of the reaction is discussed. The micro determination of isoniazid itself, and in certain pharmaceutical preparations with standard N-bromosuccinimide solution is described. The experimental error does not exceed &
The N-methylation of pyridine in vitro, using dialysed and undialysed hepatic, pulmonary, renal and brain preparations from rabbits, is described. Analysis of the quaternary metabolite, N-methylpyridinium ion, was carried out by selective ion-pair extraction and cation-exchange high-performance liquid chromatography (h.p.l.c.) using a u.v. detector, and also by direct cation-exchange h.p.l.c. of incubates containing S-adenosyl-L-[methyl-3H]methionine using a flow-through radioactivity detector. N-Methylation of pyridine could be readily demonstrated with dialysed homogenates, 9000 g and 100 000 g supernatant fractions from lung, kidney and liver, but not with any of the brain preparations. 'Pyridine N-methyltransferase' activity was confined to the tissue cytosol, and this enzyme utilized S-adenosyl-L-methionine as the methyl donor. Since the activity of the 'pyridine N-methyltransferase' in rabbit tissues is increased many fold by dialysis, this enzyme, in common with most other N-methylating enzymes, is subject to inhibition by a low-molecular-weight endogenous substance.
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