Effects of 3-methylcholanthrene, beta-naphthoflavone, and phenobarbital on the 3-methylcholanthrene-inducible isozyme of cytochrome P-450 within centrilobular, midzonal, and periportal hepatocytes.

Abstract

Rabbit antiserum produced against cytochrome P-450 MC-B, the major isozyme of cytochrome P-450 isolated from hepatic microsomes of 3-methylcholanthrene-pretreated rats, was utilized in unlabeled antibody peroxidase-antiperoxidase and indirect fluorescent antibody staining techniques to investigate the effects of 3-methylcholanthrene, P-naphthoflavone, and phenobarbital on the hemeprotein within centrilobular, midzonal, and periportal hepatocytes in livers of male rats.In livers of untreated and vehicle-pretreated rats, midzonal and periportal hepatocytes were found to bind the anti-cytochrome P-450 MC-B t o equal extents while centrilobular hepatocytes bound approximately 25% more antibody.Pretreatment of rats with phenobarbital did not result in alterations in either the intensity or pattern of immunohistochemical staining for cytochrome P-450 MC-B within the liver lobule.In livers of rats which had been pretreated with 3-methylcholanthrene, microfluorometric analyses revealed that the extent of anti-cytochrome P-450 MC-B binding increased by approximately 215% within both the midzonal and periportal regions of the lobule and by approximately 150% within centrilobular regions.Pretreatment of rats with p-naphthoflavone resulted in alterations in the hemeprotein which were similar to those produced by 3-methylcholanthrene. Thus, after rats had been pretreated with either 3-methylcholanthrene or 8-naphthoflavone, the pattern of intralobular distibution of cytochrome P-450 MC-B was altered so that the antibody bound to approximately equal extents to hepatocytes within the three regions of the lobule.These results demonstrate that 3-methylcholanthrene and P-naphthoflavone exert similar inductive effects on cytochrome P-450 MC-B within the liver lobule, with the least degree of induction of the hemeprotein being produced within centrilobular hepatocytes.Extensive evidence has been presented for the presence of several isozymes of cytochrome P-450 within hepatocytes (1- 5).The different forms of the hemeprotein are associated with microsomal, nuclear, and mitochondrial membranes where they mediate the oxidative metabolism of a multitude of