CELLULAR-LOCALIZATION OF THE CLASS-I ALCOHOL-DEHYDROGENASE TRANSCRIPTIN ADULT-RAT TISSUES

The mammalian class I alcohol dehydrogenase is the principal enzyme re sponsible for ethanol metabolism. While it is regarded primarily as a liver-specific enzyme, class I alcohol dehydrogenase is known to be pr esent in a number of extrahepatic tissues. The purpose of the current study is to define the tissue and cellular distribution of the dehydro genase transcript in four rat tissues previously shown to contain high levels of mRNA: the liver, the proximal small intestine, the colon an d the testis. Localization of the transcript was examined in formalin- fixed, paraffin-embedded rat tissues by in situ hybridization using ra dioactively labelled antisense rat alcohol dehydrogenase RNA probe. In the liver, the dehydrogenase message is localized primarily to the pe rivenous hepatocytes. In the proximal small intestine and the colon, t he message follows a vertical gradient of distribution along the crypt -villus and the crypt-surface epithelium axes, respectively, with the base of the crypt exhibiting the greatest concentration. In the testis , the message is localized primarily to cells in the interstitium. The se findings illustrate a highly compartmentalized nature of distributi on of the class I alcohol dehydrogenase transcript in the tissues stud ied and may help to elucidate the metabolic functions of this enzyme i n these tissues.