Zinc absorption in rats fed a low-protein diet and a low-protein diet supplemented with tryptophan or picolinic acid.

Zinc absorption was examined in rats fed a basal diet with 5% vitamin-free casein, in rats fed the 5% casein-based diet supplemented with tryptophan and in rats fed the 5% casein-based diet supplemented with picolinic acid. True, total daily zinc absorption was determined by an isotope dilution technique after the rats had been injected intramuscularly with carrier-free 65Zn. The zinc concentration of the kidneys from the rats fed the 5% casein diet was significantly less than that of the kidneys from rats fed the same diet supplemented with either tryptophan or picolinic acid. The specific activity of Zn in the kidneys from the rats fed the low-protein diet was significantly greater than that of the kidneys from rats fed the diet supplemented with either tryptophan or picolinic acid. The specific activity of Zn in the feces from rats fed the low-protein diet was significantly less than the specific activity of the feces from rats fed either supplemental tryptophan or supplemental picolinic acid. True, total daily zinc absorption in rats fed the low-protein diet was significantly less than the total daily zinc absorption in rats fed either supplemental tryptophan or supplemental picolinic acid. Since tryptophan is a metabolic precursor of picolinic acid, the results support the hypothesis that endogenous and exogenous picolinic acid facilitates zinc absorption.