RENAL PREGLOMERULAR ARTERIAL–VENOUS O₂ SHUNTING IS A STRUCTURAL ANTI‐OXIDANT DEFENCE MECHANISM OF THE RENAL CORTEX

Abstract

1. High blood flow to the kidney facilitates a high glomerular filtration rate, but total renal O2 delivery greatly exceeds renal metabolic requirements. However, tissue Po2 in much of the renal cortex is lower than may be expected, being similar to that of other organs in which perfusion is closely matched to metabolic demand. 2. The lower than expected renal cortical Po2 is now attributed largely to diffusional shunting of as much as 50% of inflowing O2 from blood within preglomerular arterial vessels to post-glomerular venous vessels. However, the functional significance of this O2 shunting remains unclear. Indeed, this mechanism may appear maladaptive, given the kidney's susceptibility to hypoxic insults. 3. We hypothesize that renal preglomerular arterial-venous O2 shunting acts to protect the kidney from the potentially damaging consequences of tissue hyperoxia. The diffusion of O2 from arteries to veins within the kidney acts to reduce the O2 content of the blood before it is distributed to the renal microcirculation. Because high tissue Po2 may increase the production of reactive oxygen species, we suggest that renal arterial-venous O2 shunting may provide a physiological benefit to the organism by limiting O2 delivery to renal tissue, thereby reducing the risk of cellular oxidation.

Regional decreases in renal oxygenation during graded acute renal arterial stenosis: a case for renal ischemia

“…Moreover, the reduced O 2 efficiency for sodium reabsorption may reflect the increased impact of medullary O 2 consumption occurring due to a shifting of reabsorption from paracellular to transcellular pathways, resulting in increased stoichiometric energy requirements. Furthermore, arteriovenous shunting (12,18,25) may also occur during progressive renal arterial stenosis and warrants further investigation.…”

“…Because of the parallel arrangement of descending and ascending vasa recta, important for the concentrating mechanism, the kidney is subjected to "shifting" or shunting of arterial O 2 to the venous side (11,16,25). Shunting accounts for both the higher O 2 concentration in the renal vein with respect to the superficial cortex and for the very low O 2 concentration in the renal papilla (3,25).…”

Measurement of Renal Tissue Oxygen Tension: Systematic Differences between Fluorescence Optode and Microelectrode Recordings in Anaesthetized Rabbits

“…Our aim was to consider the relative merits of these techniques for estimating interstitial oxygen tension, which should be in relative equilibrium with the oxygen tension of peritubular capillaries. A reliable estimate of peritubular oxygen tension within various regions of the kidney, in turn, would facilitate investigation of the mechanisms controlling intrarenal oxygenation [4, 8]. Our report takes advantage of data from a previously published study in which we measured responses of renal tissue oxygen tension to alterations in renal blood flow and arterial blood oxygen tension [9].…”

Intrarenal oxygenation: unique challenges and the biophysical basis of homeostasis

“…We present a case to support the concept that arterial-to-venous (AV) oxygen shunting might make an important contribution to the dynamic physiological regulation of kidney oxygenation and also to the development of renal hypoxia in kidney disease. This is a controversial proposition because much of the evidence supporting a dynamic role of AV O 2 shunting is indirect and recent (46,55) or based largely on theoretical considerations (84). Nevertheless, we believe that its incorporation into conceptual models of kidney oxygenation may foster rapid advances in this field.…”