Basal renal O₂consumption and the efficiency of O₂utilization for Na⁺reabsorption

Abstract

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.

Determinants of renal tissue hypoxia in a rat model of polycystic kidney disease

“…It might also be that the efficiency of oxygen utilization for sodium reabsorption is reduced in the kidney of LPK rats. However, our current limited observations are not sufficient for us to tease out basal renal oxygen consumption from oxygen consumption dependent on sodium reabsorption in Lewis and LPK rats (14). Oxidative stress has been implicated in the pathogenesis of both acute and chronic kidney disease (30,32,44).…”

Endothelin type A receptor inhibition normalises intrarenal hypoxia in rats used as a model of type 1 diabetes by improving oxygen delivery

“…In the present study, QO 2 was unaltered whereas TNa was significantly reduced after ETA-R inhibition, resulting in a lower TNa/QO 2 . It is well-known that the TNa/QO 2 ratio should be interpreted with caution when experimentally altering TNa (reviewed by Evans et al [44]). The lack of an acute effect of ETA-R inhibition on total kidney QO 2 is possibly the result of ETA-Rs mainly being localised in the smooth muscle cells and myocytes, and not in the renal tubular cells performing the majority of work in the kidney.…”

Modeling oxygen consumption in the proximal tubule: effects of NHE and SGLT2 inhibition

“…By extrapolation, Evans et al (7) estimated that this ratio ranges between ϳ10 and 45% in rats under normal conditions (i.e., with FE Na ϭ 1%). We assume here that, in the proximal tubule, Q O2 basal remains constant and equal to 20% of total O 2 consumption (Q O 2 ) under baseline conditions.…”

“…Reported values of T Na /Q O 2 for the whole kidney range between 15 and 25 in the rat (4,7,53). The efficiency of oxygen utilization for Na ϩ transport increases with the passive-to-active Na ϩ reabsorption ratio.…”

“…Q O2 basal may nevertheless vary with Na ϩ transport rates. For the whole kidney, a recent compilation of 24 studies indicates that the basal-tototal Q O 2 ratio spans a wide range, from 0 to 80% (7). Part of Q O2 basal may be utilized for the production of glucose (i.e., gluconeogenesis) or triacylglycerol, depending on the availability of other substrates and the metabolic state of the tissue (20).…”