ABSTRACT
PIP: The excretion of urinary tryptophan metabolites was studied in normal and postmenopausal women and in women taking norethindrone and ethinyl estradiol, singly and in combination. The results showed that the altered tryptophan metabolism found in the preovulatory phase of the cycle and in postmenopausal women was the result of an interaction between Vitamin-B6 and endogenous sex hormones. During the preovulatory phase, endogenous estradiol disrupted the normal activity of the Vitamin-B6-dependent quinolinic acid decarboxylase, which resulted in the accumulation of bladder carcinogens in urine. During the postovulatory phase, endogenous progesterone and the production of metabolites antagonized this effect. Administration of naturally occurring progesterone and of ethinyl estradiol, alone and in combination with norethindrone, was able to counter the interaction between Vitamin-B6 and endogenous estradiol. It is suggested that the cyclic excretion pattern of endogenous bladder carcinogens in young, nonpregnant women may contribute, in part, to the low incidence of bladder cancer in women.^ieng