Hepatic mono-oxygenase activity and hepatocellular morphology in chickens treated with 3-methylcholanthrene

Hepatic drug metabolism in the chicken was investigated. White leghorn chickens were administered 20 mg of 3-methylcholanthrene (3MC) per kg 72 and 48 hr before killing. Levels of hepatic cytochrome P-450 were increased approximately 4-fold. In vitro ethylmorphine N-demethylase (ND) activity was enhanced approximately 1.7-fold, aniline hydroxylase (AH) was increased 2.5-fold, aryl hydrocarbon hydroxylase was increased 20-fold, and NADPH-cytochrome c reductase was unchanged. The Vmax was increased for both ND and AH activities, but the KM for demethylation was depressed whereas that for hydroxylation of aniline was increased. The metabolism of hexobarbital in vivo was not enhanced by 3MC treatment. In brief, the distinctive features of the hepatic mono-oxygenase system of the 3MC-treated chicken were: (a) enhanced ethylmorphine N-demethylase activity, (b) a shift in the Soret peak in the CO-difference spectrum of reduced cytochrome P-450 from the control value of 452 nm to 449 nm, and (c) proliferation and pronounced vesiculation of the hepatic endoplasmic reticulum as revealed by electron-microscopic examination.