Catechol-O-Methyltransferase Activity in Cholestatic Rat's Liver Induced by Bile Duct Ligation

To investigate the cause of increased plasma catecholamine levels in liver disease, catechol-O-methyltransferase (COMT), which provides a major route of catabolism for circulating catecholamines, was studied under the cholestasis induced by mechanical biliary obstruction in rats. Monoamine oxidase (MAO) activity and the $K_m$ and $V_{max}$ values for both enzymes were also measured. Cytosolic, microsomal, and mitochondrial COMT activities in the cholestatic liver were significantly decreased throughout the experiment. Microsomal, and mitochondrial MAO activity in the cholestatic liver were also significantly decreased. Vmax values of COMT and MAO were lower. Serum COMT and MAO activities were detected after CBD ligation. These results indicate that plasma catecholamine levels are increased in liver disease due to decreased hepatic degradation of catecholamines by decreased activities of COMT and MAO. The decreased activity of these enzymes is caused by decreased biosynthesis and by flowage into the blood from the damaged hepatocyte.