Histology and survival in age-delayed low-tryptophan-fed rats.

Diets containing tryptophan in concentrations 30 and 40 percent of those fed to controls from weaning to 24-30 months or more, can delay aging in Long-Evans female rats. Mortality among low-tryptophan-fed rats was greater in the juvenile period, but substantially less than controls at late ages. Histological biomarkers of aging were also delayed after tryptophan restriction in some organs (liver, heart, uterus, ovary, adrenal and spleen) but not in others (kidney, lung, aorta). Brain serotonin levels were low in tryptophan-deficient rats but showed remarkable capacity for rehabilitation. Effects on early and late mortality and brain levels of serotonin were proportional to the severity of the restriction.