Comparative Toxicity of Halothane, Isoflurane, Hypoxia, and Phenobarbital Induction in Monolayer Cultures of Rat Hepatocytes

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Abstract
Hypoxia, phenobarbital induction, and halothane anesthesia have been implicated in the pathogenesis of hepatotoxicity in the rat model. However, a controversy exists over the role of halothane in liver injury; does it act by reducing hepatic blood flow, thereby inducing hypoxia, or do its metabolites initiale the injury? These variables are difficult to separate during in vivo halothane exposure. In the present experiments, effects of halothane on hepatic perfusion were eliminated by exposing confluent monolayers of hepatocytes isolated from Fisher 344 rats livers, both with and without phenobarbital pretreatment, to 1.5% halothane or 2.0% isoflurane in 1%, 2%, or 4% (control) oxygen. Isoflurane exposure was included for a control of anesthetic effects on hepatocytes, because it is known to be metabolized minimally and probably is not associated with hepatic dysfunction. Oxygen levels were chosen to approximate those that may occur in the liver in vivo. Cell death was assayed via aspartate aminotransferase (AST) release, both immediately following a 2-h oxygen ± anesthetic exposure and 6 h post-exposure. Per cent cell death data were analyzed using multiple regression techniques. Results obtained immediately, and 6 h after, exposure demonstrate that low oxygen levels, halothane, and phenobrbital were each highly significant factors (P <.001) in relation to cell death, in agreement with the halothane-phenobarbital-hypoxia rat model. A toxic effect of isoflurane was not observed under identical experimental conditions. The results of the study clearly indicate that the origin of cell death in hepatocyte monolayers is multi-factorial; hypoxia, phenobaribital induction, and halothane exposure each contribute to the hepatocyte damage observed in our in vitro model.