POTENTIATION OF HYPOXIC INJURY IN CULTURED RABBIT HEPATOCYTES BY THE QUINOXALINONE ANXIOLYTIC, PANADIPLON

The quinoxalinone anxiolytic, panadiplon, produces hepatic metabolic i nhibition (mitochondrial impairment), microvesicular steatosis and cen trilobular necrosis in rabbits. Metabolic inhibition occurs in culture d hepatocytes without cytotoxicity, suggesting that hepatic injury is influenced by additional factors. The present experiments were conduct ed to determine if metabolic inhibition by panadiplon predisposed hepa tocytes to hypoxic injury. Injury (cell death) was evaluated by lactat e dehydrogenase (LDH) release from cells; ATP and glycogen levels were also evaluated. Under hypoxic conditions, control cultures showed a 6 .5-fold increase in LDH release compared to normoxic controls, with a coincident 80% decrease in ATP and 50% decrease in glycogen levels. Un der normoxic conditions, 10 mu g/ml panadiplon treatment for 48 h redu ced ATP and glycogen levels by 40% but did not cause an increase in LD H leakage. Cells treated with panadiplon, then exposed to hypoxia cond itions, showed a significant level of injury compared to normoxic cont rol cultures, and a further reduction in ATP. No additional decrease i n glycogen was observed. In an attempt to prevent panadiplon-mediated injury, glycolytic substrates (dihydroxyacetone or pyruvate) were incl uded during normoxic and hypoxic incubations. Both cotreatments reduce d the level of LDH leakage produced by panadiplon during hypoxia. Cotr eatment did not generally increase ATP or glycogen levels (compared to panadiplon treatment groups) during hypoxia, though individual experi ments showed a slight increase in ATP levels. During normoxia both cot reatments with panadiplon resulted in significantly higher glycogen le vels than in panadiplon cultures alone. These results suggest that cel lular glycogen and subsequently ATP levels are reduced during panadipl on exposure, metabolically predisposing hepatocytes to hypoxic injury.