Changes in the urinary excretion of the metabolites of the tryptophan-niacin pathway during pregnancy in Japanese women and rats.

NAD is biosynthesized from tryptophan. Therefore, experimental studies including tryptophan metabolism studies could provide insight into niacin nutrition in pregnancy. Our aim was to determine the change in niacin metabolism during pregnancy by a systemic investigation of how pregnancy alters the tryptophan-niacin metabolism in Japanese women and rats. For the human study, spot urine samples were collected from a total of 434 pregnant Japanese women who were at 5-40 wk of gestation, 50 women at 4-6 wk postpartum, and 10 nonpregnant women as the controls. For the animal study, pregnant rats were fed with a niacin-free diet, and daily urine samples were collected from day 6 of gestation to day 6 postpartum. The intermediates and metabolites of the tryptophan-niacin pathway in the urine samples were measured. The urinary excretions of niacin metabolites in humans and rats increased from mid pregnancy in a time-dependent manner, reached a peak of 2-3-fold during late pregnancy, and declined to control levels after childbirth.