The Interactions between Vitamin B6 and Hormones

Abstract

Treatment with estrogen-containing oral contraceptives causes elevated urinary excretions of xanthurenic acid, kynurenine, 3-hydroxykynurenine, and 3-hydroxyanthranilic acid. It is found that in addition to tryptophan metabolites, women taking estrogen-containing oral contraceptives excrete increased levels of N'-methylnicotinamide, but not N′-methyl-2-pyridone-5-carboxamide, in urine collected with or without tryptophan loading. Estradiol disulfate and diethylstilbestrol sulfate, the ester of a nonsteroidal estrogen, are the most potent inhibitors, the former being effective at a concentration as low as 0.5 μM. A number of vitamin B6-dependent enzymes are inducible by estrogens, either directly or because estrogen treatment causes an increase in the level of circulating glucocorticoids, which in turn stimulates enzyme protein synthesis. Erythrocyte alanine aminotransferase and aspartate aminotransferase activities are widely used indicators of vitamin B6 nutritional status in humans. It is found that erythrocyte alanine aminotransferase and aspartate aminotransferase activities, and the degree of stimulation in vitro by pyridoxal phosphate, were similar in oral contraceptive users and controls before the consumption of the vitamin B6-deficient diet, and, as depletion progressed, the groups showed similar changes in the two enzymes.