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Earlier investigations on the metabolism of pyridoxine in animals have involved the study of degradation products by chemical methods and microbiological assay procedures (1-5).The present knowledge of the metabolism of Vit. Be (pyridoxine, pyridoxamine: and pyridoxal) in man and other animals, obtained by using these procedures. has been summarized by Snell (6). Low recoveries of ingested or injected pyridoxine in previous metabolic studies in animals have led to the speculation that a portion of the "missing" pyridoxine is excreted in conjugated forms as yet unidentified. An alternate hypothesis for the low recoveries would be that the ingested drug was stored in the tissues. This latter explanation was discounted by Rabinowitz and Snell(5) on the basis that no great storage oi the vitamin would be expected in normal animals, and on the fact that excretion levels rapidly returned to base levels in human subjects. The present study of the turnover times and urinary and fecal excretion of H3-pyridoxine was undertaken to investigate these hypotheses further.Methods. Tritium-( H3) labeled pyridoxine hydrochloride was obtained by exchange of pyridoxine borate in tritium water over platinum catalyst ( 7). Chemical and radioactive purity was established by paper chromatography. Specific activity of the H:;pyridoxine hydrochloride was 308 pc/mg. The solution used for injection contained 2 mg (616 pc) of labeled and 18 mg of unlabeled pyridoxine hydrochloride/ml. All injections were intravenous via the jugular *Work performed under the auspices of U. S. Atomic Energy Commission.--sinus route. The rats weighed between 250 and 350 g . Rat A received 184.8 pc H3pyridoxine HCl. Rats B and C received 369.6 pc, while rats D through K received 616 pc H3-pyridoxine HCl. Following injection of the drug, the rats were placed individually in standard meta.bulism cages.Rats A, B, and C had blood and urine samples taken at various time intervals post injection. Urine and fecal samples were cdlected from rats D to K for detailed urinary and fecal excretion and chromatographic studies .Blood and urine specimens were measured for tritium using the liquid scintillation-d,ioxane system as described previously by Richmond et d ( 8 ) . The feces were homogenized in distilled water, decolorized with charcoal, and counted as above. The counting efficiency of each sample was determined with the use of an internal standard. All calculations were in absolute counting rates (dpm) and results expressed as % of injected dose.All urine specimens obtained up to 5% hours after injection were chromatographed by the descending methd(9). One-tenth ml of urine was placed directly on No. 1 Whatman filter paper strips. In all instances, this was a t least 5 X l oG dpm of H3 activity.Eighty per cent propanol was the solvent system used. It was necessary to expose the chromatogram strips to X-ray film for at least 4 weeks to get satisfactory exposures on the film. Results.Concentrations of H3 activity in blood as a function of time after administration of l...

In most instances of metabolic antagonism the essential metabolite and the inhibitory agent have been similar in chemical structure. The structural appearance of isoniazid: lead to the speculation that its mode of action might represent interference with the utilization of nicotinamide or some other essential metabolite of similar structure. This report deals with the screening of certain vitamins, some of which are structurally similar to isoniazid, for possible isoniazid reversal.Materials and methods. The method chosen to study the mode of action of isoniazid was similar to that of hlcIlwain ( 1 ) , and Lampen and Jones (2 ) . \7arious organisms with known nutritional requirements were inhibited with the drug and reversal of the inhibition was initially attempted with nicotinic acid, nicotinamide, pyridoxine, thiamine, riboflavin, pantothenic acid, and p-aminobenzoic acid. Studies were later limited to pyridoxine and its derivatives when the initial results showed that only these compounds gave a competitive reversal of inhibition. The final steps were to study the effects on various species of Mycobacterium. No attempt was made to study any organism in any medium when a concentration of greater than M of the isoniazid was required for inhibition. The organisms employed in this study were obtained from the American Type Culture Collection, Washington, D.C., unless otherwise stated. Synthetic medita were used whenever possible to control the amount of essential metabolites present. Some comparisons were made between synthetic and nonsynthetic media and Table I lists the organisms, media, references, and the method of measuring and detecting growth. Lactobacillus plantarum (arabinosus) 17-5 was chosen because of its wide external *Work done under the auspices of the AEC. t Sandia Base with station at Los Alamos. $ Kindly supplied as Nydrazid by Squibb and Co., and as Rimifon by Hoff mann-LaRoche, Inc. nutritional requirements which included those of major interest, nicotinic acid and pyridoxine. I t also discriminates between pyridoxine and its derivatives, pyridoxal and pyridoxamine, the latter 2 being more active than pyridoxine as growth promoters. In all experiments using LactobaciElus changes in growth were observed grossly over 72 hours and the medium titrated for acid production at that time. Streptococcus pyogenes was used only because of its external pyridoxine requirement. Saccharomyces carlsbergensis was chosen because of its use in assay of vit.B6 and its uniform response to BG and its derivatives. Final turbidity readings for determination of growth were made after 18 hours incubation at 30°C. The effect of isoniazid inhibition was studied in relation to: the growth of 2 Escherichia coli strains which do not require added B6, one mutant strain of which requires nicotinic acid or its amide. The final turbidity readings were made after 18 hours incubation at 37°C. The E. coEi strains are similar to the Mycobacteyium which also have no external requirement for pyridoxine or its derivatives. Both are k...

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