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  • Title: Effects of oral contraceptives on tryptophan metabolism and vitamin B6 requirements in women.
    Author: Brown RR, Rose DP, Leklem JE, Linkswiler HM.
    Journal: Acta Vitaminol Enzymol; 1975; 29(1-6):151-7. PubMed ID: 1244084.
    Abstract:
    To evaluate the effect of oral contraceptive usage on the nutritional requirement for vitamin B6, control women and oral contraceptive users were depleted of vitamin B6 for 1 month followed by a month of repletion with 0.8, 2.0, or 20.0 mg of pyridoxine hydrochloride per day. At weekly intervals a number of indices of vitamin B6 nutrition were measured. Marked elevation in excretion of tryptophan metabolites occurred in oral contraceptive users after tryptophan loads. However, other indices of vitamin B6 nutritional state, including urinary 4-pyridoxic acid excretion, urinary cystathionine excretion, plasma pyridoxal phosphate concentrations, and erythrocyte aspartate and alanine aminotransferases were not different between controls and oral contraceptive users. The excretion of metabolites after oral loading doses of L-kynurenine (which bypasses tryptophan oxygenase) was elevated in oral contraceptive users indicating that abnormal metabolism of tryptophan was not due only to induced tryptophan oxygenase. The data indicate that use of oral contraceptives does not generally change the requirement for vitamin B6 but rather produces a specific change in activity of enzymes beyond kynurenine in the pathway of tryptophan metabolism. 10 healthy control women (mean age 22.3 years) and 15 women (23.2 years) who had used oral contraceptives (OCs) for at least 6 months were given a diet low in vitamin-B6 containing the equivalent of .19 mg of pyridoxine/day for 4 weeks. All subjects were started on the study at the same time in their menstrual cycle. After this depletion period, subjects continued to ingest the same diet but with daily supplements of .8, 2, or 20 mg of pyridoxine hydrochloride for another 4 weeks. Before starting the depletion diet, and at weekly intervals throughout the study, several indexes of vitamin-B6 nutrition were measured in each subject. Marked elevation in excretion of trytophan metabolites occurred in OC users after tryptophan loads. However, other indexes of vitamin-B6 nutritional state, including urinary 4-pyridoxic acid excretion, urinary cystathionine excretion, plasma pyridoxal phosphate concentrations, and erythrocyte asparate and alanine aminotransferases, were not different between controls and OC users. The excretion of metabolites after oral loading doses of L-kynurenine (which bypasses tryptophan oxygenase) was elevated in OC users, indicating that abnormal metabolism of tryptophan was not due only to induced tryptophan oxygenase. The data indicate that OC use does not generally change the requirement for vitamin-B6, but rather produces a specific change in activity of enzymes beyond kynurenine in the pathway of tryptophan metabolism.
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