Hydroperoxide metabolism in rat liver

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Abstract
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 Ba2+ (1 mM), by 30% in Ca2+‐free perfusions and was decreased by 50–60% when the intracellular Ca2+ 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 Ba2+. 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 H2O (n= 18), due to a slight stimulation of prostaglandin‐D2 release under the influence of the hydroperoxide. In the presence of Ba2+ (1 mM), t‐butylhydroperoxide increased the perfusion pressure by 12.7 ± 1.2 cm H2O (n= 9) and produced an approximately tenfold increase of prostaglandin‐D2 and thromboxane‐B2 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‐D2 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 Ba2+‐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.