Physiological consequences of oxygen-dependent chloride binding to hemoglobin.

The PO(2)-dependent binding of chloride to Hb decreases the Cl(-) concentration of the red blood cell (RBC) intracellular fluid in venous blood to approximately 1-3 mmol/l less than that in arterial blood. This change is physiologically important because 1) Cl(-) is a negative heterotropic allosteric effector of Hb that competes for binding sites with 2,3-bisphosphoglycerate and CO(2) and decreases oxyhemoglobin affinity in several species; 2) it may help reconcile several longstanding problems with measured values of the Donnan ratios for Cl(-), HCO, and H(+) across the RBC membrane that are used to calculate total CO(2) carriage, ion flux rates, and membrane potentials; 3) it is a factor in the change in the dissociation constant for the combined nonvolatile weak acids of Hb associated with the Haldane effect; and 4) it diminishes the decrease in strong ion difference in the RBC intracellular fluid that would otherwise occur from the chloride shift and prevent the known increase of HCO concentration in that compartment.

Hyperoxic reperfusion exacerbates postischemic renal dysfunction.

BACKGROUND: Hyperoxic reperfusion from global ischemia worsens functional outcome because of oxygen radical-mediated injury. This study tested the hypothesis that hyperoxic reperfusion would exacerbate postischemic renal dysfunction. METHODS: Twenty-nine healthy, uninephrectomized, male mongrel rabbits (Oryctolagus cuniculus) in 3 groups were subjected to 30 minutes of complete normothermic renal ischemia followed by reperfusion under hyperoxic or normoxic conditions. The groups were: hyperoxically reperfused (n = 8), normoxically reperfused (n = 8), hyperoxic sham (no ischemia, n = 5), and allopurinol-pretreated (50 mg/kg, intravenously), hyperoxically reperfused animals (n = 8). Plasma concentrations of creatinine, urea nitrogen and electrolytes were measured at 0, 24, 48, and 72 hours after ischemia and served as functional outcome markers. Histopathologic analysis of kidneys for injury was performed by an expert who was blinded to the procedures. RESULTS: Plasma creatinine in hyperoxically reperfused rabbits was significantly elevated above normoxic (P =.02) and sham (P =.003) animals by 48 hours and remained elevated to 72 hours. Plasma urea nitrogen in hyperoxically reperfused rabbits was significantly elevated above the normoxic group (P = .01), the sham group (P = .02), and the allopurinol group (P = .04) by 72 hours. These coincided with a significantly elevated histopathologic injury score in hyperoxically reperfused rabbits compared with sham (P = .019), normoxic (P = .035), and allopurinol-pretreated hyperoxically reperfused animals (P = .037). CONCLUSIONS: Hyperoxic reperfusion exacerbates renal dysfunction after 30 minutes of complete normothermic ischemia. This dysfunction may be mediated by oxygen radical-related injury.