Effects of Aroclor 1254 on cytochrome P-450-dependent monooxygenase, glutathione S-transferase, and UDP-glucuronosyltransferase activities in channel catfish liver

Channel catfish (Ictalurus punctatus) were treated with single intraperitoneal injections of Aroclor 1254, ranging from 1-100 mg Aroclor 1254/kg body wt, and effects of the Aroclor on several xenobiotic-metabolizing enzymes were evaluated. Hepatic microsomal monooxygenase (MO) activity toward 7-ethoxyresorufin, 7-ethoxycoumarin and benzo[a]pyrene was increased in a dose-dependent manner. 7-Ethoxyresorufin-O-deethylase activity was increased by a dose of 1 mg Aroclor 1254/kg, whereas 7-ethoxycoumarin-O-deethylase and benzo[a]pyrene hydroxylase activities were increased by doses of 10 mg/kg and higher. Maximal increases in MO activity ranged from three- to 15-fold, depending upon the substrate used. Treatment with 100 mg Aroclor 1254/kg increased hepatic cytosolic glutathione S-transferase (GST) activity toward 1,2-epoxy-3-(p-nitrophenoxy)propane about 20%; however, GST activity toward four other substrates was unaffected. Also, hepatic microsomal UDP-glucuronosyl-transferase (UDPGT) activity was increased about two-fold in catfish treated with 100 mg Aroclor 1254/kg. Treatment with doses of Aroclor 1254 lower than 100 mg/kg did not significantly increase either GST or UDPGT activities. Although MO, GST, and UDPGT activities all were increased by Aroclor 1254, the MO system was by far the most sensitive. Because these enzyme systems are functionally linked in the biotransformation of certain xenobiotics, differential effects, such as those produced by Aroclor 1254, could alter patterns of xenobiotic metabolism and toxicity.