Blockade of the renin-angiotensin system and renal tissue oxygenation as measured with BOLD-MRI in patients with type 2 diabetes

Aim: To assess whether blockade of the renin-angiotensin system (RAS), a recognized strategy to prevent the progression of diabetic nephropathy, affects renal tissue oxygenation in type 2 diabetes mellitus (T2DM) patients. Methods: Prospective randomized 2-way cross over study; T2DM patients with (micro) albuminuria and/or hypertension underwent blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI) at baseline, after one month of enalapril (20 mg qd), and after one month of candesartan (16 mg qd). Each BOLD-MRI was performed before and after the administration of furosemide. The mean R-2* (=1/T-2*) values in the medulla and cortex were calculated, a low R-2* indicating high tissue oxygenation. Results: Twelve patients (mean age: 60 +/- 11 years, eGFR: 62 +/- 22 ml/min/1.73 m(2)) completed the study. Neither chronic enalapril nor candesartan intake modified renal cortical or medullary R-2* levels. Furosemide significantly decreased cortical and medullary R-2* levels suggesting a transient increase in renal oxygenation. Medullary R-2* levels correlated positively with urinary sodium excretion and systemic blood pressure, suggesting lower renal oxygenation at higher dietary sodium intake and blood pressure; cortical R-2* levels correlated positively with glycemia and HbA1c. Conclusion: RAS blockade does not seem to increase renal tissue oxygenation in T2DM hypertensive patients. The response to furosemide and the association with 24 h urinary sodium excretion emphasize the crucial role of renal sodium handling as one of the main determinants of renal tissue oxygenation. (C) 2012 Elsevier Ireland Ltd. All rights reserved.