Tissue B-6 Vitamer Concentrations in Rats Fed Excess Vitamin B-61

Abstract

Diets containing 1, 10, 100, 175 or 250 times the NRC recommended level of pyridoxine HCl (7 mg/kg) were fed to rats (218 g, 12 per group) to evaluate the effects on tissue B-6 vitamer concentrations. After 10 wk, food intake and body weights did not differ among groups. Overt toxicity was not observed. Tissues were taken from five rats of each group after overnight food deprivation (unfed rats); the remaining seven rats in each group were allowed access to food (fed rats). In plasma of unfed rats, 4-pyridoxic acid and pyridoxal concentrations increased significantly (P < 0.05) with increasing dietary pyridoxine; pyridoxal phosphate was not affected by dietary pyridoxine. Concentrations of pyridoxal phosphate and pyridoxal increased significantly with increasing dietary pyridoxine in erythrocytes of unfed rats. Excretion of urinary B-6 vitamers and 4-pyridoxic acid in a 24-h period increased with dietary pyridoxine in fed rats. As dietary pyridoxine was increased, kidney pyridoxal concentrations increased significantly in fed rats only. Dietary pyridoxine did not affect vitamer concentration in muscle and liver of either unfed or fed rats, or in brain of unfed rats. Muscle glycogen phosphorylase, which contains pyridoxal phosphate, was not affected by dietary pyridoxine. There was a marginally significant (P = 0.058) increase in erythrocyte alanine, but not in aspartate, aminotransferase activity with increasing dietary pyridoxine. Plasma concentration of pyridoxal phosphate, which is used as a measure of vitamin B-6 status, did not reflect intake of pyridoxine in this study. Likewise, muscle pyridoxal phosphate and glycogen phosphorylase, advanced as possible reservoirs of vitamin B-6 because of positive correlations with dietary vitamin B-6 under some conditions, were unresponsive to excess dietary vitamin B-6.