Furosemide reverses medullary tissue hypoxia in ovine septic acute kidney injury

In experimental sepsis, the rapid development of renal medullary hypoxia precedes the development of acute kidney injury (AKI) and may contribute to its pathogenesis. We investigated whether inhibiting active sodium transport and oxygen consumption in the medullary thick ascending limb with furosemide attenuates the medullary hypoxia in experimental septic AKI. Sheep were instrumented with flow probes on the pulmonary and renal arteries and fiber optic probes to measure renal cortical and medullary perfusion and oxygen tension (Po-2). Sepsis and AKI were induced by infusion of live Escherichia coli. At 24 h of sepsis there were significant decreases in renal medullary tissue perfusion (1.332 +/- 233 to 698 +/- 159 blood perfusion units) and Po-2 (44 +/- 6 to 19 +/- 6 mmHg) (both P < 0.05). By 5 min after intravenous administration of furosemide (20 mg). renal medullary Po-2 increased to 43 +/- 6 mmHg and remained at this normal level for 8 h. Furosemide caused transient increases in fractional excretion of sodium and creatinine clearance, but medullary perfusion, renal blood flow, and renal oxygen delivery were unchanged. Urinary F-2-isoprostanes, an index of oxidative stress, were not significantly changed at 24 h of sepsis but tended to transiently decrease after furosemide treatment. In septic AKI, fumsemide rapidly restored medullary Po-2 to preseptic levels. This effect was not accompanied by changes in medullary perfusion or renal oxygen delivery but was accompanied by a transient increase in fractional sodium excretion, implying decreased oxygen consumption as a mechanism.