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<正>The effects of various inducers and inhibitors on cardiac microsomal carboxylesterase (CE) activities toward p-nitrophenylacetate(PNPA)were studied in comparison with the hepatic CE in male rats.Phenobarbital treatment(80mg/kg,ip)increased the liver,but not cardiac CE activities.Clofibrate(300mg/kg,ip) and dexamethasone(10mg/kg,ip) increased the enzymatic activities of both the liver and heart CEs.The in vitro effects of various inhibitors on PNPA hydrolyzing activities of the cardiac and hepatic CEs were different.In the case of cardiac CE of control rats,the Vmax and Km were 143 nM/min/mg protein and 0.41mM,respectively.While Ki values of bis-p-nitrophenylphosphate(BNPP)which is a specific inhibitor of CE,phenylmethylsulfonylfluoride(PMSF ) and diisopropylfluorphophate (DFP)were 1.0,0.8 and 0.54μM,respectively.In liver CE of control rats, Vmax Km were 6.6μM/min/mg protein and 0.34μM,respectively.While,the Ki values of the three inhibitors(BNPP,PMSF and DFP)were 1.1,1.2 and 0.67μM,respectively.In conclusion,the effects of various inducers and inhibitors on the cardiac and hepatic microsomal CE activities in rats seem to the different from each other.