Regulation of renal cytochrome P-450. Effects of two-thirds hepatectomy, cholestasis, biliary cirrhosis and post-necrotic cirrhosis on hepatic and renal microsomal enzymes.

The possibility of a relationship between hepatic and renal cytochrome P-450 contents was assessed in rats with liver disease. In rats killed 3 days after two-thirds hepatectomy (a model for hepatocellular insufficiency), the total microsomal cytochrome P-450 content of the whole liver was decreased by 60% as compared to that in control rats; renal cytochrome P-450 was increased by 30% while the 7-ethoxycoumarin deethylase activity of kidney microsomes was increased by 80%. In rats killed 7 days after bile duct ligation (a model for cholestasis) or 35 days after bile duct ligation (a model for biliary cirrhosis), hepatic cytochrome P-450 was decreased by 60% and 45%, respectively, while renal cytochrome P-450 content was increased by 50% and 150%, respectively. In contrast, in rats killed 15 days after the last dose of carbon tetrachloride, 1.3 ml/kg twice weekly for 3 months (a model for post-necrotic cirrhosis), both hepatic and renal cytochrome P-450 contents remained unchanged. Phenobarbital (80 mg/kg daily for 3 days) was a poor inducer of renal cytochrome P-450 in sham-operated rats but became a potent inducer of renal cytochrome P-450 in rats with two-thirds hepatectomy. We conclude that renal cytochrome P-450 is increased in three models in which hepatic cytochrome P-450 contents are decreased (two-thirds hepatectomy, cholestasis and biliary cirrhosis), but remains unchanged in a model of severe liver pathology, in which hepatic cytochrome P-450 content is not modified (late, post-necrotic cirrhosis). The hypothetical role of endogenous inducer(s) is discussed.

Effect of fasting on metabolite-mediated hepatotoxicity in the rat.

Acetaminophen and bromobenzene are transformed in the liver into chemically reactive metabolites that may either bind to glutathione and be detoxified or bind to hepatic proteins and produce liver cell necrosis. Fasting for 42 hr (a) decreased hepatic glutathione concentration, (b) increased the amount of chemically reactive metabolite irreversibly bound to hepatic proteins after administration of 3H-acetaminophen or 14C-bromobenzene, and (c) increased the hepatotoxicity of acetaminophen or bromobenzene. In rats fasted for various lengths of time, there was an inverse relationship between the concentration of glutathione in the liver and the activity of serum glutamic pyruvic transaminases after administration of acetaminophen or bromobenzene. In vitro, there was an inverse relationship between the concentration of glutathione in the incubate and the amount of chemically reactive metabolite bound to microsomal proteins after incubation of 3H-acetaminophen or 14C-bromobenzene with hepatic microsomes. It is concluded that fasting may decrease the inactivation of chemically reactive metabolites by glutathione, increase their binding to hepatic proteins, and enhance the hepatotoxicity of drugs transformed into chemically reactive metabolites that are detoxified by binding to glutathione.