Extrahepatic Biotransformation of Halothane and Enflurane

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Abstract
The rates of biotransformation of halothane and enflurane by rabbit kidney and lung microsomal preparations were compared to the hepatic microsomal biotransformation of these agents. All three microsomal preparations (pulmonary, renal, and hepatic) were found capable of performing oxidative demethylation reactions as well as epoxidation. This was evidenced by the ability of these three microsomal preparations to metabolize benzphetamine, methoxyflurane, and trichloroethylene. Only the liver microsomal preparations were capable of defluorinating enflurane at any appreciable rate (6 ± 3 pmoles/min/mg of microsomal protein). The three microsomal preparations performed reductive biotransformation of halothane, and the liver microsomes produced more than 3 times as much product as the other tissues. Pulmonary and renal microsomal preparations metabolized halothane reductively about equally. Differences in the solubility of halothane and enflurane in the rabbit pulmonary and hepatic microsomes were not found to be a cause of the differences in biotransformation in these two organs. Extrahepatic biotransformation may be an important factor in the disposition of volatile anesthetics.

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