Induction of Drug-Metabolizing Enzymes by Long-Term Administration of PCB and Duration of Their Induced Activities in Carp

A study was made of the induction of drug-metabolizing enzymes by a long-term administration of PCB-diet and also the duration of their induced activities in the hepatopancreas of carp Cyprinus carpio. In a preliminary experiment comparing the inductivity of hepatic drug-oxidase, PCB among the tested environmental contaminants was most effective as the inducer of cytochrome P-450. Therefore, a subsequent experiment was performed to elucidate the effect of long-term administration of PCB (0.05 mg/100 g-body weight/day) for 16 weeks on drug-metabolizing enzymes in the hepatopancreas of carp. The dietary administration of PCB induced not only the cyt. P-450 content and the activities of aryl hydrocarbon hydroxylase and O-dealkylase, but also the glutathione content and the activities of glutathione- and UDPglucuronosyl-transferase. However, the increase of these contents and activities during PCB administration occurred mostly within 2- or 4-week period, resulting in almost no further increase in spite of the continuous PCB administration for 16 weeks. The induced contents and activities were kept for a fairly long time even after discontinuance of PCB administration.