Reversal of the Behavioral and Electrophysiological Abnormalities of An Animal Model of Hepatic Encephalopathy by Benzodiazepine Receptor Ligands

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Abstract
Behavioral and electrophysiological evidence implicating the GABA–benzodiazepine receptor complex in the pathogenesis of hepatic encephalopathy was obtained using an improved rat model of hepatic encephalopathy caused by thioacetamide–induced fulminant hepatic failure. After the administration of thioacetamide together with supportive therapy, acute hepatocellular failure developed in rats as a result of massive hepatocellular necrosis without evidence of renal failure or hypoglycemia. The evolution of hepatic encephalopthy in this model was sufficiently slow to readily permit the staging of the syndrome. Prominent features of the encephalopathy include a marked reduction in open field activity and an abnormal visual evoked response. Both the deficits in spontaneous motor function and visual evoked response abnormalities of rats in stages III to IV hepatic encephalopathy were significantly improved after the administration of the benzodiazepine receptor ligands flumazenil or Ro 15–4513. Doses of flumazenil or Ro 15–4513 that produced these effects in rats with hepatic encephalopathy had no detectable action on either the behavior or the visual evoked responses of normal rats. The ability of benzodiazepine receptor ligands to ameliorate both the behavioral depression and the visual evoked response abnormalities associated with hepatic encephalopathy in the thioacetamide–induced rat model suggest an involvement of the GABA/benzodiazepine receptor complex in the pathogenesis of hepatic encephalopathy. In addition, the similarity of these observations to those in rabbits with hepatic encephalopathy caused by galactosamine–induced fulminant hepatic failure is compatible with the hypothesis that the mechanisms of hepatic encephalopathy in these two distinct models share a common final pathway, the allosteric enhancement of GABAergic tone through the benzodiazepine receptor. These observations suggest that increased concentrations or availability of a ligand with agonist properties at the benzodiazepine receptor may be involved in the pathogenesis of hepatic encephalopathy and that administration of benzodiazepine receptor antagonists may be of value in the management of hepatic encephalopathy in man. (Hepatology 1990; 11: 371-378.)