Halothane hepatotoxicity in hyperthyroid rats as compared to the phenobarbital-hypoxia model.

Halothane hepatotoxicity was observed after exposing hyperthyroid rats to 0.625% halothane for 4 hr under hypoxic conditions (10% O2). In this model, increases in serum enzyme activities of the alanine aminotransferase (GPT) and the sorbitol dehydrogenase (SDH) were evident immediately following exposure and were six-fold higher than in the phenobarbital-hypoxic model. Plasma free-fluoride levels estimated immediately after exposure to halothane were increased twofold in halothane-exposed hyperthyroid rats under hypoxic conditions as were increased twofold in halothane-exposed hyperthyroid rats under hypoxic conditions as compared to a sixfold increase in the phenobarbital-hypoxic model. The concentration of glutathione in liver was more markedly decreased in hyperthyroid rats than in phenobarbital-induced rats. The fact that no clear-cut correlation was found between defluorination and hepatotoxicity in both models may favor the hypothesis that a non-defluorinated metabolite of halothane, e.g., 2-chloro-1,1,1-trifluoroethyl radical, is the reactive intermediate responsible for the liver lesions. On the other hand, intracellular hypoxia due to hypermetabolism during the hyperthyroid state may be the reason for the higher sensitivity of hyperthyroid rats.