We examined how the presence of a fixed level of basal renal O2 consumption (V̇O2 basal; O2 used for processes independent of Na+ transport) confounds the utility of the ratio of Na+ reabsorption (TNa+) to total renal V̇O2 (V̇O2 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 V̇O2 basal to V̇O2 total under physiological conditions (basal percent renal V̇O2). Estimates of basal percent renal V̇O2 from 24 studies varied from 0% to 81.5%. Basal percent renal V̇O2 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 V̇ O2 of 12.7-16.5% when FENa+ = 1% (r2 = 0.48, P = 0.001). Experimentally induced changes in TNa+ altered TNa+/V̇O2 total in a manner consistent with theoretical predictions. We conclude that, because V ̇O2 basal represents a significant proportion of V̇O2 total, TNa+/V̇O2 total can change markedly when TNa+ itself changes. Therefore, caution should be taken when TNa+/V̇O2 total is interpreted as a measure of the efficiency of O2 utilization for TNa+, particularly under experimental conditions where TNa+ or V̇O2 total changes.
- Efficiency of oxygen utilization for sodium reabsorption
- Oxygen consumption
- Renal metabolism
ASJC Scopus subject areas