MICROSOMAL LAURIC ACID HYDROXYLASE-ACTIVITIES AFTER TREATMENT OF RATS WITH 3 CLASSICAL CYTOCHROME-P450 INDUCERS AND PEROXISOME PROLIFERATING COMPOUNDS

In order to investigate a proposed relationship between induction of hepatic microsomal lauric acid hydroxylase activity and peroxisome proliferation in the liver, male Wistar rats were treated with peroxisome proliferating compounds, and the lauric acid hydroxylase activity, the immunochemical detectable levels of cytochrome P450 4A1 and the activities of peroxisomal enzymes were determined. In addition, the levels of cytochrome P450 4A1 and lauric acid hydroxylase activities were studied after treatment of rats with three cytochrome P450 inducers. After treatment with aroclor-1254, phenobarbital or 3-methylcholanthrene total cytochrome P450 was 1.7-2.7 times induced. However, no induction of lauric acid omega-hydroxylase activities or P450 4A1 levels were found. After treatment of rats with di(2-ethylhexyl)phthalate (DEHP) a dose-dependent induction of lauric acid-omega-hydroxylase activities, levels of cytochrome P450 4A1 and peroxisomal fatty acid beta-oxidation was found. Even at a dose-level of 100 mg DEPH/kg body weight per day a significant induction of these activities was observed. The main metabolites of DEHP, mono(2-ethylhexyl)phthalate and 2-ethyl-1-hexanol, also caused an induction of levels of P450 4A1, lauric acid-omega-hydroxylase activities and the activity of peroxisomal palmitoyl-CoA oxidase. 2-Ethyl-1-hexanoic acid did not influence lauric acid-omega-hydroxylase activities, but did induce levels of P450 4A1 and palmitoyl-CoA oxidase activities. Three other compounds (perfluoro-octanoic acid, valproate and nafenopin) induced both lauric acid-omega-hydroxylase activity and peroxisomal palmitoyl-CoA oxidase activity. The plasticizer, di(2-ethylhexyl)adipate, did not induce levels of P450 4A1, lauric acid-omega-hydroxylase activities or palmitoyl-CoA oxidase activities. With the compounds tested a close association between the induction of lauric acid-omega-hydroxylase activities and peroxisomal palmitoyl-CoA oxidase activity was found. These data support the theory that peroxisome proliferating compounds do induce lauric acid omega-hydroxylase activities and that there might be a mechanistic inter-relationship between peroxisome proliferation and induction of lauric acid-omega-hydroxylase activities.