Factors influencing halothane hepatotoxicity in the rat hypoxic model

Halothane, a widely used inhalation anesthetic, was shown to be hepatotoxic to male, phenobarbital-pretreated rats, only when administered under hypoxic conditions (fraction of inspired oxygen = 0.14). The degree of hepatotoxicity as determined from morphological alterations and serum glutamic-pyruvic transaminase (SGPT) activities, correlated well with concentrations of hepatic cytochrome P-450 and concentration of inspired halothane. Maximal lesion intensity developed within 12 to 24 hr after exposure to 1% halothane for as little as 30 min. By 4 days after exposure, the liver had repaired, since no morphological alterations were apparent and SGPT activities had returned to normal values. Female rats, when pretreated with phenobarbital and exposed to 1% halothane under hypoxic conditions did not develop liver injury. SKF-525A and metyrapone reduced the severity of liver injury when administered preanesthesia and 4 hr postanesthesia. The free sulhydryl-containing compounds, cysteine, cystamine, and N-acetylcysteine afforded protection when administered at 4 or 8 hr (cystamine) after ending anesthesia. These results support the hypothesis that reductive or noxoxygen-dependent biotransformation of halothane results in toxic intermediates that can initiate halothane-induced liver injury.