Abstract
Intraperitoneal 3-methylcholanthrene induces hepatic aryl hydrocarbon (benzo[a]pyrene) hydroxylase (EC 1.14.14.2) in the C57BL/6N mouse about 5-7-fold; a dose of 8O mg/ kg of body weight maintains maximal levels on the second through the seventh day after a single injection. The same dose of β-naphthoflavone induces the hydroxylase about 4-fold, the maximal level occurring 40 hr, and the activity returning to basal levels 72 hr, following a single injection. Dose-response studies, time-response studies, simultaneous treatment with maximal and submaximal amounts of both inducers, and multiple-injection experiments all suggested that β-naphthoflavone is absorbed from the peritoneal cavity much more rapidly than 3-methylcholanthrene. With radiolabeled inducers, it was confirmed that β-naphthoflavone is absorbed from the peritoneal cavity into the liver and blood and is excreted (presumably as metabolites) in the feces and urine about 10 times more rapidly than 3-methylcholanthrene during the first 12-18 hr after a single injection of 80 mg/kg of body weight. Concomitant with the rise and fall, respectively, in β-naphthoflavone- or 3-methylcholanthrene-induced aryl hydrocarbon hydroxylase activity are (a) increases and decreases in microsomal total cytochrome P-450 content; (b) a spectral shift to the blue, and then back toward the red, in the Soret peak of the reduced cytochrome-CO complex; and (c) and decreases in two bands (having molecular weights of about 55,500 and 54,500) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Which of the two bands is associated with the induced hydroxylase activity remains to be determined (or perhaps both bands are). Similar results were found with β-naphthoflavone- and 3-methylcholanthrene-treated sexually immature male Sprague-Dawley rats. These data indicate a common mechanism of induction of hepatic cytochrome(s) P-448 by β-naphthoflavone and 3-methylcholanthrene.
ACKNOWLEDGMENTS We wish to thank Ms. Nancy M. Jensen for her invaluable technical assistance in this study.
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