Tryptophan and neutral amino acids in premenstrual syndrome.

An abnormality of the serotonin system may play a role in the genesis of the symptoms of premenstrual syndrome, especially those related to mood and appetite. Whole blood and platelet uptake of serotonin are decreased during the luteal phase in women with premenstrual syndrome. The ratio of L-tryptophan (the amino acid precursor of serotonin) to the sum of the other neutral amino acids that compete for the same protein carrier cerebral uptake mechanism has been suggested to reflect central L-tryptophan levels and resultant serotonin levels in the brain. We evaluated the ratio of plasma L-tryptophan to the sum of five competing neutral amino acids in women with premenstrual syndrome and in controls. There were no significant differences between groups or across time, suggesting that it is unlikely that the aberrations of the serotonergic system in women with premenstrual syndrome are due to saturation of the tryptophan-carrying protein.