Metabolism of Tritium-Labeled Pyridoxine in Rats.

Abstract

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...

The absorption of tritium-labelled pyridoxine HCl in control subjects and in patients with intestinal malabsorption

“…Failure to excrete unts of radiomore of the administered radioactivity must reflect technique is some alternative metabolic pathway than urinary vitamin B12 excretion. A similar situation has been recorded in applied to the studies of the metabolism of 3H-pyridoxine in the ne in the rat rat (Cox, Murray, and Boone, 1962). ation that the In six out of 13 patients with idiopathic steators the urinary rhoea there was evidence of impaired absorption of rther indicates pyridoxine, for they excreted less radioactivity in loxine behaves the urine than any of the control subjects (Table III).…”

Dietary Reference Values for vitamin B6

“…In studies using labelled PN in humans (Tillotson et al., ) or rats (Cox et al., ), only about 3% of the ingested dose of vitamin B6 is excreted through the faeces. Using labelled isotopes, the excretion of 4‐PA in urine is similar in either conventional and germ‐free guinea pigs or rats (Coburn and Townsend, ).…”

Vitamin Tolerance of Animals

“…Differences have been reported in the efficiency of absorption and retention of this vitamin among species. Following an administered dose of PN, the amount recovered in urine was 50 to 70 percent for the rat (Cox et al, 1962), 20 percent for the dog (Scudi et al, 1940), and less than 10 percent for HYPERVITAMINOSIS Adverse effects following the ingestion of elevated amounts of folic acid to animals have not been observed. The vitamin is generally regarded as nontoxic.…”