Local maximum oxygen disappearance rate has limited utility as a measure of local renal tissue oxygen consumption

Introduction: Methods for measurement of local oxygen consumption (VO₂) are required to allow development of treatments for kidney disease that target kidney oxygen dysregulation. In anaesthetized rabbits, we determined whether local oxygen disappearance rate (ODR) during complete renal ischaemia reflects tissue VO₂ in the kidney and in hindlimb skeletal muscle (biceps femoris). Methods: Whole kidney VO₂ was determined under conditions employed to alter oxygen consumption. The ureter was ligated to reduce VO₂ (n=6) or the mitochondrial uncoupler 2,4-dinitrophenol was administered to increase VO₂ (n=6). An additional 10 rabbits were studied which received neither treatment. Immediately following VO₂ measurements, oxygen partial pressure (PO₂) was measured, over the first 60s after abrupt cardiac arrest, using fluorescence optodes and in a subset of experiments (n=6), Clark electrodes. Parallel experiments were performed in hindlimb skeletal muscle (biceps femoris). Results: ODR in the renal cortex and medulla, and in biceps femoris, was linear during the first ~15s after cardiac arrest (r²≈0.98). Using fluorescence optodes, maximum ODR averaged across all 22 rabbits in which the kidney was studied was -0.75±0.09 and -0.60±0.06mm Hg/s respectively in the renal cortex and medulla. Maximum ODR averaged across all 10 rabbits in which the biceps femoris was studied was -0.30±0.06mm Hg/s. ODR increased at greater initial PO₂ only in the renal cortex. ODR in neither the renal medulla nor biceps femoris varied with whole organ VO₂, although renal cortical ODR normalized for initial PO₂ was significantly correlated with whole organ VO₂ (r²=0.19). Maximum ODR obtained by Clark electrode was approximately four-fold greater than that obtained by fluorescence optode. Discussion: Because ODR correlates poorly with whole organ VO₂, it likely has limited utility as a measure of local VO₂.