Effect of Sodium Loading/Depletion on Renal Oxygenation in Young Normotensive and Hypertensive Men

Abstract

Abstract-The goal of this study was to investigate the effect of sodium intake on renal tissue oxygenation in humans. To this purpose, we measured renal hemodynamics, renal sodium handling, and renal oxygenation in normotensive (NT) and hypertensive (HT) subjects after 1 week of a high-sodium and 1 week of a low-sodium diet. Renal oxygenation was measured using blood oxygen level-dependent magnetic resonance. Tissue oxygenation was determined by the measurement of R2* maps on 4 coronal slices covering both kidneys. The mean R2* values in the medulla and cortex were calculated, with a low R2* indicating a high tissue oxygenation. Ten male NT (mean age: 26.5Ϯ7.4 years) and 8 matched HT subjects (mean age: 28.8Ϯ5.7 years) were studied. Cortical R2* was not different under the 2 conditions of salt intake. Medullary R2* was significantly lower under low sodium than high sodium in both NT and HT subjects (28.1Ϯ0.8 versus 31.3Ϯ0.6 s Ϫ1; PϽ0.05 in NT; and 27.9Ϯ1.5 versus 30.3Ϯ0.8 s Ϫ1 ; PϽ0.05, in HT), indicating higher medullary oxygenation under low-sodium conditions. In NT subjects, medullary oxygenation was positively correlated with proximal reabsorption of sodium and negatively with absolute distal sodium reabsorption, but not with renal plasma flow. In HT subjects, medullary oxygenation correlated with the 24-hour sodium excretion but not with proximal or with the distal handling of sodium. These data demonstrate that dietary sodium intake influences renal tissue oxygenation, low sodium intake leading to an increased renal medullary oxygenation both in normotensive and young hypertensive subjects. (Hypertension. 2010;55:1116-1122.)

Blood oxygenation level-dependent MRI for assessment of renal oxygenation

“…A role for dietary sodium intake as a confounder in BOLD MRI studies was demonstrated by Pruijm et al, 19 who showed that medullary oxygenation was higher after salt loading of sodium-depleted normotensive and hypertensive young men (n=18). The authors demonstrated enhanced proximal tubule sodium reabsorption under low sodium intake conditions, which they postulated led to reduced medullary oxygen consumption by reducing distal sodium delivery and solute transport.…”

Paradigm Shifts in Atherosclerotic Renovascular Disease

“…24 Our human studies focus on tissue oxygenation in both essential hypertension and renovascular disease, using formal measurements of cortical and medullary deoxyhemoglobin as measured by blood oxygen level-dependent (BOLD) MR under standardized conditions of sodium balance and antihypertensive drug therapy. 25 BOLD MR consistently demonstrates large gradients in tissue oxygenation with remarkably low levels of deoxyhemoglobin in kidney cortex, evolving to areas of higher deoxygenation in deeper medullary areas, 25,26 confirmed with the use of oxygen probes. 27 The complexity of tissue oxygenation within the kidney reflects multiple factors, including reduced postglomerular blood supply, active oxygen consumption by energy-consuming solute transport in tubular segments, and arteriovenous shunting.…”

Measurement of kidney perfusion in critically ill Patients

“…This technique has been used to demonstrate an increase in tissue oxygenation after administration of diuretics, particularly in the medullary areas and confirmed by implanted oxygen probes [60]. Similarly, Pruijm et al [61], showed an increase in medullary oxygenation in healthy volunteers after a decrease in their salt intake. Although not a direct measure of renal blood flow, BOLD MRI might deliver valuable information as it delivers data integrating oxygen delivery and consumption.…”