Renal BOLD-MRI relates to kidney function and activity of the renin-angiotensin-aldosterone system in hypertensive patients.

Background: The renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system are key factors in the pathophysiology of hypertension. Renal hypoxia is the putative mechanism stimulating both systems. Blood oxygen level-dependent MRI (BOLD-MRI) provides a noninvasive tool to determine renal oxygenation in humans. The aim of the current study was to investigate the relation between blood pressure (BP) and kidney function with renal BOLD-MRI. Moreover, the relation between direct and indirect variables of the RAAS and sympathetic nervous system and renal BOLD-MRI was studied. Method: Seventy-five hypertensive patients (38 men) were included. Antihypertensive medication was temporarily stopped. Patients collected urine during 24 h (sodium, catecholamines), blood samples were taken (creatinine, renin, aldosterone), a captopril challenge test was performed, and ambulatory BP was measured. Results: Mean age was 58 (+/- 11) years, day-time BP was 167 (+/- 19)/102 (+/- 16) mmHg, and estimated glomerular filtration rate was 75 (+/- 18) ml/min per 1.73 m(2)). In multivariable regression analysis, renal medullary R-2*-values inversely related to estimated glomerular filtration rate (P = 0.02). Moreover, the BP-lowering effect of captopril positively related to cortical (P = 0.02) and medullary (P = 0.008) R-2*-values, as well as to P90 (P = 0.02). Conclusion: In patients with hypertension, kidney function relates to medullary R-2*-values. Activation of the RAAS is also positively related to the renal R-2*-values.