Disturbance of tryptophan metabolism and its correction during hormonal contraception

Abstract

A relative pyridoxine deficiency was found in 80 % of 100 women using oral contraceptives. This was due to disturbed tryptophan metabolism, expressed in increased xanthurenic acid (XA) excretion ( ≥ 60 μ mol 8 h ) during 8 hours following oral administration of 2 g L-tryptophan. These contraceptives contained a combination of oestrogens and progestogens. Normalization of the excretion was nearly always achieved by giving a large dose of pyridoxine hydrochloride (vitamin B6) ( 100 mg 24 h for 4 weeks). A previously normal XA excretion always showed a significant decrease after treatment with pyridoxine hydrochloride. The blood vitamin B6 concentration is not affected by the use of oral contraceptives or intramuscular medroxyprogesterone acetate (MPA) injections (150 mg every 12 weeks). In the literature, the synthetic oestrogens are regarded as responsible for the disturbance in tryptophan metabolism. The progestogen component of the combined oral contraceptives was found to exert an influence on maximum XA excretion. This could be explained by the intrinsically oestrogenic and anti-oestrogenic properties of the progestogens used. Relative pyridoxine deficiency due to disturbed tryptophan metabolism was found also in 5 out of 15 women who used MPA as contraceptive agent.