Interaction between hemoglobin and glutathione in the regulation of blood flow in normal and septic pigs

Background: Hemoglobin (Hb) induces vasoconstriction by heme group binding nitric oxide in an irreversible fashion. Recent in vitro studies indicate that the thiol groups in Hb reversibly bind nitric oxide and participate in trans-nitrosylation reactions with other thiols. Sepsis is a pathophysiologic state characterized by vasodilation mediated, at least in part, by an excessive release of nitric oxide. The role of nitrosothiols (RSNOs) in these changes is unknown. Objectives: We tested the following in a porcine model of sepsis: (i) whether glutathione (GSH) reverses the hemodynamic effects of Hb; (ii) whether GSH induces an increase in blood flow in sepsis; (iii) whether RSNO plasma concentration increases in sepsis and is related to hypotension. Design: Nonrandomized animal controlled study. Setting: Animal research facility in a university hospital. Subjects: Anesthetized pigs were monitored with a pulmonary artery catheter and ultrasonic blood flow probes in the mesenteric artery and the portal vein for measurement of systemic, mesenteric, and portal blood flows (Q TOT , Q MES , and Q POR , respectively). Four groups of pigs were studied: nonseptic, septic, nonseptic treated with Hb (stroma-free purified porcine hemoglobin), and septic treated with Hb (n = 6 in each group). Interventions: Sepsis was induced at 0 min by the administration of live Escherichia coli. Hb (400 mg/kg/hr) was administered at 240 mins, followed by glutathione (1 g iv). Measurements and Main Results: Hb induced a pressor response and a decrease in Q TOT , Q MES , and Q POR . Glutathione reversed the effects of Hb on Q MES and Q POR . In septic pigs not treated with Hb, GSH induced an increase in Q POR . RSNO plasma concentration increased after the induction of sepsis and correlated significantly with blood pressure. Conclusions: These results indicate the reversibility of the effects of Hb by GSH, probably by interactions between nitric oxide and the reduced sulfhydryl groups in Hb, and suggest a role of RSNOs in the cardiovascular changes of sepsis.