β-Adrenoceptors activate hepatic glutathione efflux through an unreported pathway

The physiological regulation of hepatic glutathione efflux by catecholamines is poorly understood. The purpose of this work was to review the role of adrenergic receptors (AR) on total glutathione (G(T)) efflux in rat liver. Two models were used: isolated hepatocytes and perfused livers. In hepatocytes 10 mu M adrenaline (Adr), but not isoproterenol (Iso) a beta-AR agonist, or phenylephrine (Phe) an alpha(1)-AR agonist, (in a Krebs-Henseleit buffer (KHB) enriched with Ca2+ and some aminoacids) increased in 13% G(T) efflux. In livers perfused with KHB, Adr or Iso at 1 mu molar doses (but not Phe) stimulated 11-fold initial velocity of G(T) release, but only during the first 2 mm of perfusion. This immediate response progressively disappeared during the following 15 min of perfusion. A second phase of G(T) efflux, observed between 2 and 14 min of perfusion, mimics the one reported earlier in isolated hepatocytes. The ED50 for Adr and Iso activation are in the range of 320 nM and 10 nM, respectively. Iso-mediated G(T) release requires Ca2+ to work, and was prevented by H89, glibenclamide, cystic fibrosis trans-membrane regulator (CFTR) antibodies, and a direct CFTR inhibitor. This short lived G(T) release system is associated to PKA activation and probably operates through CFTR.