Strain differences in the tryptophan metabolite excretion and enzyme activities along the kynurenine pathway in rats

The strain differences of the urinary excretion of the tryptophan metabolites along the kynurenine pathway and the variations of enzyme activities metabolizing the tryptophan have been studied in different strains of rats. There is a good correlation between urinary excretory values of the metabolites and enzyme activities in the same strain of rats. However, some differences appear when the data are compared among different strains. Wistar, heterozygous Gunn and Sprague-Dawley rats show similar total urinary excretion of tryptophan metabolites, while the Long Evans rats have significantly lower values, in accordance with the lower activity of tryptophan pyrrolase. Kynureninase activity is slightly but not significantly higher in Sprague-Dawley rats, in agreement with the high levels of anthranilic acid excreted. As regards kynurenine aminotransferase, Sprague-Dawley rats show lower activity in the liver, but higher activity in the kidneys in comparison to other strains of Wistar, Long Evans and heterozygous Gunn rats. The importance of considering strain differences is emphasized when making comparisons of measurements carried out in different laboratories.