Localization of high benzaldehyde dehydrogenase activity in rat upper gastrointestinal tract mucosa: a quantitative histochemical study.

An unusual aldehyde dehydrogenase (AlDH) phenotype, histochemically similar to the "tumor-associated" AlDH appearing during rat hepatocarcinogenesis, was detected in normal rat upper gastrointestinal tract tissues. This phenotype is characterized by high activities with aromatic substrates, i.e., benzaldehyde (Bz) and NADP. Frozen sections of GI tract tissue from normal rats and from liver nodules induced by a Solt-Farber protocol were evaluated for AlDH activity. A sensitive, high-resolution procedure was used in which sections are pre-incubated in nitroblue tetrazolium and then incubated at 20 degrees C in a viscous polyvinyl alcohol medium containing buffer, phenazine methosulfate, sodium azide, substrate, co-enzyme, and nitroblue tetrazolium. Incubation at a suboptimal pH of 7.0 was found to improve retention of the final reaction product and the linearity with time. Activity was quantitated by computer-assisted microscopic photometry. Intense BzDH-NADP activity was localized in the squamous epithelium of the tongue, esophagus, and fore-stomach, and in the glandular pit cells of the glandular stomach; this activity was not evident in the submucosa, muscle walls, and vessels. Little if any BzDH-NADP activity was observed in the small or large intestine, pancreas, and liver. AlDH in upper GI tissues and in liver nodules shared three characteristics: a sharp localization; a preference for Bz and NADP compared to the aliphatic substrate acetaldehyde and NAD; and a high co-enzyme-independent activity in the presence of Bz.