Acute liver failure and hyperammonemia increase peripheral-type benzodiazepine receptor binding and pregnenolone synthesis in mouse brain.

We investigated the role of brain peripheral-type benzodiazepine receptors (PBRs) and pregnenolone (a product of PBRs activation) in hepatic encephalopathy (HE)/hyperammonemia. Administration of the hepatotoxin, thioacetamide, or ammonium acetate to mice for 3 days significantly increased the number of brain PBRs (138-146% of control) and the affinity of the ligands for these receptors (2-fold). The total content of pregnenolone and its rate of synthesis in brain of the experimental animals were significantly increased. Our results suggest a novel integrated mechanism by which ammonia-induced activation of PBRs leads to elevated levels of pregnenolone-derived neurosteroids which are known to enhance GABA-ergic neurotransmission. This mechanism may play a pivotal role in pathogenesis of HE.