Long-term tryptophan restriction and aging in the rat.

Growth-retarded rats fed a tryptophan deficient diet at 21 days for periods of 6-22 months were shown to reach normal body weight when subsequently fed Purina Rat Chow. They demonstrated an increased ability over similar aged controls to recover from hypothermia induced by 3-minute whole-body ice water immersion, were able to bear litters at 17--28 months of age, showed a delay in the age of onset of visible tumors, and indicated an increase in their average lifespan at late ages. Animals fed on this diet from 3 months of age revealed a similar ability to reproduce at advanced ages, but not as marked as those placed on the diet earlier. The average lifespan (in months +/- the standard error of the mean) of the rats recovering from the long-term tryptophan-deficient diets was 36.31 +/- 2.26 while the control rats survived an average of 30.5 +/- 1.90 months. The last of 8 rats surviving the period of tryptophan-deficiency died at 45.50 months (1387 days) while the last of 14 control rats died at 41.75 months (1266 days). It is hypothesized that some kind of subtle mechanism exerts its influence on the rats during the period of tryptophan deficiency which caused an accelerated morbidity and mortality as they approached senescence approximately 1 to 2 years after refeeding. This is parallel to the situation with immature animals subjected to long-term caloric restriction and then fed on normal diets.