The effect of furosemide upon renal oxygen consumption in the human kidney

Basal renal O2 consumption and the efficiency of O2 utilization for Na+ reabsorption

We examined how the presence of a fixed level of basal renal O2 consumption (Vo2(basal); O2 used for processes independent of Na(+) transport) confounds the utility of the ratio of Na(+) reabsorption (TNa(+)) to total renal Vo2 (Vo2(total)) as an index of the efficiency of O2 utilization for TNa(+). We performed a systematic review and additional experiments in anesthetized rabbits to obtain the best possible estimate of the fractional contribution of Vo2(basal) to Vo2(total) under physiological conditions (basal percent renal Vo2). Estimates of basal percent renal Vo2 from 24 studies varied from 0% to 81.5%. Basal percent renal Vo2 varied with the fractional excretion of Na(+) (FENa(+)) in the 14 studies in which FENa(+) was measured under control conditions. Linear regression analysis predicted a basal percent renal Vo2 of 12.7-16.5% when FENa(+) = 1% (r(2) = 0.48, P = 0.001). Experimentally induced changes in TNa(+) altered TNa(+)/Vo2(total) in a manner consistent with theoretical predictions. We conclude that, because Vo2(basal) represents a significant proportion of Vo2(total), TNa(+)/Vo2(total) can change markedly when TNa(+) itself changes. Therefore, caution should be taken when TNa(+)/Vo2(total) is interpreted as a measure of the efficiency of O2 utilization for TNa(+), particularly under experimental conditions where TNa(+) or Vo2(total) changes.

Differential effects of human atrial natriuretic peptide and furosemide on glomerular filtration rate and renal oxygen consumption in humans

OBJECTIVE

Imbalance in the renal medullary oxygen supply/demand relationship can cause hypoxic medullary damage and ischemic acute renal failure. Human atrial natriuretic peptide (h-ANP) increases glomerular filtration rate in clinical acute renal failure. This would increase renal oxygen consumption due to increased tubular load of sodium. Loop diuretics are commonly used in acute renal failure. Data on the effects of loop diuretics on glomerular filtration rate and renal oxygen consumption in humans are, however, controversial. We evaluated the effects of h-ANP and furosemide on renal oxygen consumption, glomerular filtration rate, and renal hemodynamics in humans.

DESIGN AND SETTING

Prospective two-agent interventional study in a university hospital cardiothoracic ICU.

PATIENTS

Nineteen uncomplicated, mechanically ventilated postcardiac surgery patients with normal renal function.

INTERVENTIONS

h-ANP (25 and 50 ng/kg per minute, n=10) or furosemide (0.5 mg/kg per hour, n=9).

MEASUREMENTS AND RESULTS

Renal plasma flow and glomerular filtration rate were measured using the infusion clearance technique for (51)Cr-labeled EDTA and paraaminohippurate, corrected for by renal extraction of PAH. h-ANP increased glomerular filtration rate, renal filtration fraction, fractional excretion of sodium, and urine flow. This was accompanied by an increase in tubular sodium reabsorption (9%) and renal oxygen consumption (26%). Furosemide infusion caused a 10- and 15-fold increase in urine flow and fractional excretion of sodium, respectively, accompanied by a decrease in tubular sodium reabsorption (-28%), renal oxygen consumption (-23%), glomerular filtration rate and filtration fraction (-12% and -7%, respectively).

CONCLUSIONS

The filtered load of sodium is an important determinant of renal oxygen consumption. h-ANP improves glomerular filtration rate but does not have energy-conserving tubular effects. In contrast, furosemide decreases tubular sodium reabsorption and renal oxygen consumption and thus has the potential to improve the oxygen supply/demand relationship in clinical ischemic acute renal failure.