Abstract

Women using oral contraceptives of the combined oestrogen-progestogen type excrete elevated levels of a number of metabolites of the tryptophan-nicotinic acid ribonucleotide metabolic pathway in urine collected after an oral dose of the amino acid. Increased excretions of N₁-methylnicotinamide reflect an enhanced capacity for the conversion of L-tryptophan to nicotinic acid derivatives, although an additional factor responsible for the abnormal excretion of tryptophan metabolites may be interference with the coenzymic function of vitamin B₆.

Similar changes in tryptophan metabolism are observed in human subjects treated with oestrogens alone.

The possible mechanisms for this disturbance of amino acid metabolism, and its clinical significance are discussed.