Hydroperoxide metabolism in rat liver

Addition of t ‐butylhydroperoxide (0.2 mM) to isolated perfused rat liver led to a net K + release of 7.2 ± 0.2 μmol/g within 8 min and a net K + reuptake of 6.6 ± 0.4 μmol/g following withdrawal of the hydroperoxide, in line with earlier findings by Sies et al. [Sies, H., Gerstenecker, C., Summer, K. H., Menzel, H. & Flohé, R. (1974) in Glutathione (Flohé, L., Benöhr, C., Sies, H., Waller, H. D., eds) pp. 261–276, G. Thieme Publ. Stuttgart]. Net K + release roughly paralleled the amount of GSSG released from the liver under the influence of the hydroperoxide. The t ‐butylhydroperoxide‐induced K + efflux was inhibited by approximately 70% in the presence of Ba 2+ (1 mM), by 30% in Ca 2+ ‐free perfusions and was decreased by 50–60% when the intracellular Ca 2+ stores were simultaneously depleted by repeated additions of phenylephrine. t ‐Butylhydroperoxide‐induced K + efflux was accompanied by a decrease of the intracellular water space by 58 ± 14 μl/g ( n = 4), corresponding to a 10% cell shrinkage. The effect of t ‐butylhydroperoxide on cell volume was inhibited by 70–80% in the presence of Ba 2+ . In isolated rat hepatocytes treatment with t ‐butylhydroperoxide led to a slight hyperpolarization of the membrane at concentrations of 100 nM, but marked hyperpolarization occurred at t ‐butylhydroperoxide concentrations above 10 μM. t ‐Butylhydroperoxide (0.2 mM) transiently increased the portal‐perfusion pressure by 3.3 ± 0.6 cm H 2 O ( n = 18), due to a slight stimulation of prostaglandin‐D 2 release under the influence of the hydroperoxide. In the presence of Ba 2+ (1 mM), t ‐butylhydroperoxide increased the perfusion pressure by 12.7 ± 1.2 cm H 2 O ( n = 9) and produced an approximately tenfold increase of prostaglandin‐D 2 and thromboxane‐B 2 release. Under these conditions, glucose output from the liver rose from 0.9 ± 0.03 to 2.9 ± 0.7 μmol · g −1 · min −1 ( n = 4) with a time course roughly resembling that of portal‐pressure increase and prostaglandin‐D 2 overflow. These effects were largely abolished in the presence of ibuprofen or the thromboxane‐receptor‐antagonist BM 13.177. The t ‐butylhydroperoxide effects on perfusion pressure, glucose and eicosanoid output were also enhanced in the presence of insulin or during hypotonic exposure; i.e. conditions known to swell hepatocytes, but not during hyperosmotic exposure. The data suggest that t ‐butylhydroperoxide induces liver‐cell shrinkage and hyperpolarization of the plasma membrane due to activation of Ba 2+ ‐sensitive K + is apparently required for the t ‐butylhydroperoxide‐induced K + channel activation, and K + efflux may be related to cellular thiol oxidation. t ‐Butylhydroperoxide stimulates the formation of cyclooxygenase products. The data show that hydroperoxide effects on hepatic metabolism are more complex than previously thought; both, cell shrinkage and eicosanoid formation under the influence of t ‐butylhydroperoxide may contribute to its known glycogenolytic effect.