Renal oxygen content is increased in healthy subjects after angiotensin-converting enzyme inhibition

OBJECTIVE: The association between renal hypoxia and the development of renal injury is well established. However, no adequate method currently exists to non-invasively measure functional changes in renal oxygenation in normal and injured patients. METHOD: R2(star) quantification was performed using renal blood oxygen level-dependent properties. Five healthy normotensive women (50 +/- 5.3 years) underwent magnetic resonance imaging in a 1.5T Signa Excite HDx scanner (GE Healthcare, Waukesha, WI). A multiple fast gradient-echo sequence was used to acquire R2(star)/T-2(star) images (sixteen echoes from 2.1 ms/slice to 49.6 ms/slice in a single breath hold per location). The images were post-processed to generate R2(star) maps for quantification. Data were recorded before and at 30 minutes after the oral administration of an angiotensin II-converting enzyme inhibitor (captopril, 25 mg). The results were compared using an ANOVA for repeated measurements (mean +/- standard deviation) followed by the Tukey test. ClinicalTrials.gov: NCT01545479. RESULTS: A significant difference (p<0.001) in renal oxygenation (R2(star)) was observed in the cortex and medulla before and after captopril administration: right kidney, cortex = 11.08 +/- 0.56ms, medulla = 17.21 +/- 1.47ms and cortex = 10.30 +/- 0.44ms, medulla = 16.06 +/- 1.74ms, respectively; and left kidney, cortex = 11.79 +/- 1.85ms, medulla = 17.03 +/- 0.88ms and cortex = 10.89 +/- 0.91ms, medulla = 16.43 +/- 1.49ms, respectively. CONCLUSIONS: This result suggests that the technique efficiently measured alterations in renal blood oxygenation after angiotensin II-converting enzyme inhibition and that it may provide a new strategy for identifying the early stages of renal disease and perhaps new therapeutic targets.