Abstract

The organ distribution of microsomal cytochrome P 450 isoenzymes (P 450), microsomal epoxide hydrolase (EH) and cytosolic glutathione-S-transferases was investigated by immunoblotting and enzyme measurements in rats and humans. In rats, P 450 IA1 was detected only in the duodenum, and P 450 IA2 and IIC11 were detected only in the liver. The highest concentrations of P 450 IIB1/B2 were found in the lung and in the duodenum; pentoxyresorufin-O-dealkylase activity was closely correlated with the amounts of P 450 IIB1/B2 in the different organs. P 450 IIE1 was present in liver, kidney and lung, whereas EH was found in liver, intestine and kidney. In humans, P 450 IIIA4 was detected in all tissues investigated; the highest concentrations were found in liver and intestine. The P 450 IIIA4 level was closely correlated with that of erythromycin demethylase and pentoxyresorufin-O-dealkylase activities. P 450 IIC8-10, IIE1 and IID6 were expressed in liver and intestine, P 450 9 in liver and kidney and P 450 IA2 in liver. EH was identified only in liver, intestine and kidney. In both species, concentrations and total amounts of P 450 isoenzymes and EH were much lower in all extrahepatic tissues than in the liver. Conversely, glutathione-S-transferase-pi was abundant in human intestine and colon compared to liver. Glutathione-S-transferase-mu polymorphism was confirmed in all tissues investigated. This extensive study showed that the pattern of (iso) enzymes was different in all tissues studied; consequently, xenobiotic metabolism would appear to be very different in each type of tissue.