Comparative localization of aldehyde oxidase and xanthine oxidoreductase activity in rat tissues

The distribution of aldehyde oxidase activity was evaluated in unfixed cryostat sections from tissues of male Wistar rats using a tissue protectant, polyvinyl alcohol, with Tetranitro BT as a final electron acceptor. The distribution of aldehyde oxidase activity was compared with that of xanthine oxidoreductase. The enzyme histochemical method demonstrated aldehyde oxidase activity in the epithelium of the tongue, renal tubules and bronchioles, as well as in the cytoplasm of liver cells. Such activity was not detected in oesophagus, stomach, spleen, adrenal glands, small or large intestine or skeletal and heart muscle fibres. In contrast, xanthine oxidoreductase activity was demonstrated in the tongue, renal tubules, bronchioles, oesophageal, gastric, small and large intestinal epithelial cells, adrenal glands, spleen and liver cytoplasm but not in skeletal and heart muscle fibres. The significance of the ubiquitous distribution of aldehyde oxidase activity, especially in surface epithelial cells from various tissues, except for the gastrointestinal tract, is unclear. However, aldehyde oxidase may possess some physiological activity other than in the metabolism of N-heterocyclics or of certain drugs.