Oral contraceptives and tryptophan metabolism: effects of oestrogen in low dose combined with a progestagen and of a low-dose progestagen (megestrol acetate) given alone

The effect upon tryptophan metabolism of the use of combined oestrogen-progestagen oral contraceptives containing a low (0.05 mg) dose of oestrogen, or of the continuous administration of megestrol acetate, has been studied by determining the excretion of tryptophan metabolites in urine collected after a 2 g oral dose of the amino acid. An investigation of 10 women before being given oral contraceptives and after 21 days and three months of their use showed that xanthurenic acid excretion is increased within 21 days and that by three months the urinary levels of xanthurenic acid, kynurenine, 3-hydroxykynurenine, and 3-hydroxyanthranilic acid may all be elevated. Ten other women studied after taking a combined type of oral contraceptive for six months or longer excreted significantly higher levels of all four metabolites than did those who had been treated with these steroids for only three months. The abnormal urinary excretion of tryptophan metabolites was completely reversed by treatment with pyridoxine hydrochloride, 20 mg daily for one month. Studies of four women when they were taking an oestrogen-containing oral contraceptive and at intervals after they had discontinued its use showed that abnormal tryptophan metabolism may persist for three months or longer. Megestrol acetate, a progestagen used as an oral contraceptive, was found to have no significant effect upon tryptophan metabolism.The possible clinical significance of the effects of oral contraceptives upon tryptophan metabolism is discussed.

The effect of tryptophan load and vitamin B 6 supplementation on urinary excretion of tryptophan metabolites in human male subjects

1. Urinary excretion of tryptophan metabolites of the kynurenine pathway before and after a loading dose of 2 g of l-tryptophan (both before and during supplementation with vitamin B6) was studied in normal young male subjects and in elderly male subjects with prostatic diseases.

2. The increase in urinary excretion of tryptophan metabolites in the normal male subjects after a loading dose of 2 g of l-tryptophan was unchanged after vitamin B6 supplementation, indicating that this dose does not exceed the normal capacity of the kynurenine pathway.

3. It is therefore concluded that a loading dose of 2 g of l-tryptophan is preferable when studying the capacity of the kynurenine pathway.

4. In about three-quarters of the elderly male subjects with prostatic diseases, the capacity of the kynurenine pathway was normal.

5. In about one-quarter of the subjects with prostatic diseases after a loading dose of 2 g of l-tryptophan there was abnormally high urinary excretion of one or several tryptophan metabolites, which could be normalized by vitamin B6, indicating that the capacity of the kynurenine pathway had been exceeded in these subjects.

6. Urinary excretion of individual tryptophan metabolites after a loading dose of 2 g of l-tryptophan was constant in the same subject when studied under unchanged conditions, whether there was a normal or a decreased capacity of the kynurenine pathway.

7. It is concluded that a single determination of urinary excretion of tryptophan metabolites after a loading dose of 2 g of l-tryptophan is sufficient to determine the capacity of the kynurenine pathway.

Effects of acetylsalicylic acid on serum protein binding and metabolism of tryptophan in man

In normal persons, ingestion of aspirin causes a release of tryptophan from its binding site on serum albumin. There is a fall in bound and total serum tryptophan concentrations and a rise in free tryptophan concentrations. The urinary excretion of 3-hydroxyanthranilic acid is decreased, that of xanthurenic acid is increased and that of 3-hydroxykynurenine was increased in 4 out of 6 subjects, indicating an effect on the enzyme systems involved in the metabolism of tryptophan. Conjugates of these metabolites were shown to interfere with the method of assay of the unconjugated hydroxy acids by column chromatography. To overcome this difficulty all urine samples were first boiled in molar hydrochloric acid to hydrolyse any conjugates present. Any results obtained using non-hydrolysed urines would be misleading. This work shows that it is important to take account of the drugs used in treatment before ascribing changes in tryptophan metabolism to pathological states.