Effect of Oral Administration of L-Cystine on Hypotaurine Level in Rainbow Trout

Abstract

To elucidate the cysteine metabolism in rainbow trout, the tissue levels of metabolites derived from dietary cyst(e)ine were examined. First, the distribution of hypotaurine among tissues was examined for the rainbow trout fed a commercial diet. Hypotaurine content was highest in the liver (1.2μmol per g tissue), followed by the kidney (0.3μmol per g tissue) but it was not detectable in the brain or the blood. The value obtained in the liver was far higher than the values that have been reported for fish so far. Effects of dietary administration of excess cystine on the changes in the tissue levels of metabolites were examined. The excess cystine administration increased the level of hypotaurine in the tissues. The level of cysteine sulfmate also tended to increase, but the quantity was very small compared with that of hypotaurine. Although cysteine sulflnate may play an important role also in cysteine metabolism in rainbow trout as well as mammals, cysteine sulfinate seems to be quickly metabolized into hypotaurine.