The metabolism of urocanic acid, imidazolelactic acid, and D-histidine in the intact rat.

Interest has recently been revived in the possibility that urocanic acid may be an intermediate in the metabolism of L-histidine (1). In the rat, both Cox and Rose (2) and Harrow and Sherwin (3) found this product ineffective in the dietary replacement of histidine. However, neither it nor imidazolelactic acid has been tested for its capacity to promote liver glycogen deposition, which would serve as an index of comparison with another known behavior of n-histidine (4). So far as we are aware, none of the D isomers of the essential amino acids has been tested for its capacity to promote growth when supplied parenterally. This paper records comparative data for glycogen formation after the administration of n-histidine, rAmidazolelactic acid, and urocanic acid. Since such production might well be influenced by differences in rates of absorption, these were also determined. The paper also presents results obtained in tests of growth promotion conducted to determine the capacity of L-histidine, n-histidine, rAmidazolelactic acid, and urocanic acid to supplement a histidine-deficient diet, whether injected subcutaneously or fed.