Leakage of Monoamine Oxidase from Rat Liver after Hepatic Ischemia or Administration of the Hepatotoxin Allyl Formate

Abstract

Monoamine oxidase (MAO) activities in rat liver perfusate obtained by perfusion with sucrose buffer and lipid peroxide and superoxide dismutase (SOD) activity levels in liver tissue were investigated after pretreatment of rats with total hepatic ischemia or the perilobular hepatotoxin allyl formate. MAO activities in rat liver perfusate assessed with β-phenylethylamine and 5-hydroxytryptamine as substrates and liver tissue lipid peroxide of these rats were increased, but SOD activity was decreased. The accumulation of lipid peroxides was partly attributed to the decreased activity of SOD as a consequence of membrane disorders. When allyl formate was administered to the rats, amine oxidase activities in plasma were not completely inhibited by MAO inhibitors (clorgyline or deprenyl), and the activity measured with 1μM benzylamine as substrate was elevated. However, the complete inhibition of amine oxidase activities in the perfusates was obtainable and the activity toward 1μM benzylamine was not observed. The K_m values of these amine oxidases for β-phenylethylamine and 5-hydroxytryptamine were the same as those of liver mitochondrial MAO. These results suggest that MAO in liver mitochondria was released into the blood as a consequence of membrane disorder but that two or more other distinct amine oxidase activities that were detected in the plasma were not released from the liver.