The differences in growth and activity of the tryptophan-NAD pathway between Wistar and Sprague Dawley strains of rats fed on tryptophan-limited diet.

Three-week-old weanling rats of Wistar and Sprague Dawley strains were fed on tryptophan-limited and nicotinic acid-free diets for 46 days and the following was observed. (1) Gain in body weight of the Sprague Dawley strain was significantly higher than that of the Wistar strain from the 10th day of feeding. (2) Tryptophan oxygenase [EC 1.13.11.11]activity in the Wistar strain was constant but was significantly increased in the Sprague Dawley strain during the latter period of this experiment. (3) The total amount of nicotinic acid, quinolinic acid, N1-methylnicotinamide and tryptophan in liver and kidney of the Sprague Dawley strain was significantly higher than that of the Wistar strain. (4) Total urinary nicotinic acid, quinolinic acid and N1-methylnicotinamide levels were not very different between the two strains, but it was observed that at the 38th day the levels in the Sprague Dawley strain were significantly higher than those in the Wistar strain. From the above result, it was presumed that the Sprague Dawley strain of rat was more resistant to deficiency of nicotinic acid than the Wistar strain fed on a low tryptophan and nicotinic acid-free diet. Aminocarboxymuconate-semialdehyde decarboxylase [EC 4.1.1.45] activities in livers of both strains dropped to half the original value at the end of the experiment. This change may indicate metabolic control of increase in flow from tryptophan to NAD.