Despite the thousands of investigations that have been conducted on drug metabolism per se, on enzymes that participate in drug metabolism (activation as well as detoxication), and on the induction of drug biotransformations and drug-metabolizing enzymes, we still know very little regarding the actual sites at which drugs and other xenobiotics are metabolized within tissues. Moreover, little is known regarding the capabilities of specific regions or cell types within complex mammalian tissues to metabolize drugs and other xenobiotics. The long-term objective of the research described in this application is to provide this important, fundamental information. To this end, the goal of the present research project is to determine where drug metabolism and its induction occur in situ within the liver, skin, and lung, three of the major organs in which drugs and other xenobiotics are metabolized. The studies described in this application have, thus, been designed to assess the relative capabilities of hepatocytes within the three regions of the liver lobule to metabolize xenobiotics, to determine how and where within the liver lobule drug-metabolizing enzymes and monooxygenase activities can be altered as a consequence of enzyme induction, to determine progressive alterations in hepatic drug-metabolizing enzymes and monooxygenase activities during 2-acetylaminofluorene-induced hepatocellular carcinogenesis, and, finally, to determine where drugs and other xenobiotics can be metabolized within the skin and lung and how and where within these tissues drug metabolism can be induced. To achieve these aims, the following methods will be employed: qualitative and semiquantitative immunohistochemical and immunocytochemical techniques which allow for investigations on the localizations and distributions of cytochrome P-450 isozymes, NADPH-cytochrome P-450 reductase, epoxide hydrolase, and glutathione S-transferases at the light microscopic level within tissues and at the electron microscopic level within cells; histochemical techniques which permit for investigations on the localizations and distributions of xenobiotic monooxygenase activities (e.g., benzo(a)pyrene and aniline hydroxylase and 7-dethoxyresorufin O-deethylase activities) at the light microscopic level within tissues; and autoradiographic techniques which allow for determinations of the intratissue and intracellular sites at which metabolites of xenobiotics formed in vivo bind covalently. The results to be forth-coming from these investigations will, therefore, very greatly advance our knowledge of the pharmacological-morphological relationship involved in drug metabolism.
