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.
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