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

Abstract 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 R2 * (=1/ T2 *) values in the medulla and cortex were calculated, a low R2 * indicating high tissue oxygenation. Results Twelve patients (mean age: 60 ± 11 years, eGFR: 62 ± 22 ml/min/1.73 m2 ) completed the study. Neither chronic enalapril nor candesartan intake modified renal cortical or medullary R2 * levels. Furosemide significantly decreased cortical and medullary R2 * levels suggesting a transient increase in renal oxygenation. Medullary R2 * levels correlated positively with urinary sodium excretion and systemic blood pressure, suggesting lower renal oxygenation at higher dietary sodium intake and blood pressure; cortical R2 * 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.