The goal of this project is to evaluate the chronic effect (8 weeks) of RASILEZ 300mg (aliskiren) on renal tissue oxygenation in patients with stage 1-2 hypertension, and to compare the chronic effect (8 weeks) of RASILEZ 300mg (aliskiren) on renal tissue oxygenation in patients with stage 1-2 hypertension with these effects with those of ESIDREX 25mg (hydrochlorothiazide).

36 patients with arterial hypertension stage 1-2 (blood pressure: 140/90 and 180/110 mm Hg) will be included in this study and randomized to two groups of 18 patients each: one group will receive RASILEZ 300mg (aliskiren) and one group ESIDREX 25mg (hydrochlorothiazide).

After a two week washout of antihypertensive drugs, baseline and the chronic effect (8 week study drug) of each group will be studied with precise renal hemodynamic measurements (inulin clearance, PAH renal plasma and blood flow, sodium and endogenous lithium excretion, plasma renin, plasma aldosterone, urinary sodium and potassium) and assessment of renal oxygenation with BOLD-MRI (blood oxygen level detection - magnetic resonance imaging).

Drug therapy will be started with an initial 2 weeks on Rasilez 150 mg or HCTZ 12.5 mg followed by a titration to 300 mg Rasilez and 25 mg HCTZ if the treatment is well tolerated. In both groups: a first baseline measurements will be performed before initiating therapy and a second after 8 weeks of treatment (24h after last drug intake) to assess the chronic effect.

Patients already on treatment with antihypertensive drugs can be included in this study, but will undergo a 'wash-out' period of two weeks. After obtaining informed consent, baseline physical examination and office blood pressure measurement will be performed. Office blood pressure will be measured according to the guidelines of the European Society on Hypertension and European Society of Cardiology (ESH-ESC practice guidelines) by an experienced physician. Moreover, patients will measure their home blood pressure twice daily: after 5 minutes of sitting quietly, three measures spaced by 1-2 minutes will be taken in the morning and in the evening. For this purpose, an Omron 705 IT device will be provided to the participants; this device has been widely tested in clinical practice and has been validated for use in clinical studies (12).

Throughout the study, the participants will continue his/her regular diet. The goal should be to keep the salt intake as stable as possible during the study, since salt intake alters the R2* signal. Salt intake will be verified each time before BOLD-MRI measurement by a 24h urine collection (dosing volume, creatinine- and sodium-concentration).

To complete the study we decid to test the acute effect of aliskiren 300mg and Esidrex (hydrochlorthiazide) 25mg in 6 healthy volunteers. We will measure the cortical and medullary R2* signal before drug intake and 3 hours after drug administration. Each participant will take the two drugs in a randomised crossover design. A wash-out period of two week between the two administration will be implemented.

Inclusion Criteria:

• Tolerance to study drugs
• Age > 18 years
• Arteria hypertension stage 1-2 (blood pressure: 140/90 and 180/110 mm Hg)
• Normal renal function
• Availability to give informed consent

Exclusion Criteria:

• Intolerance to study drugs
• Renal artery stenosis
• Hyperkalaemia > 5.0 mmol/l
• Contra-indications to the use of PAH, inulin or Lithium
• Asthma
• Pychiatric illness
• No estimated easy vascular venous access for placement of two peripherical venous catheters in forearms
• Contra-indication to MRI-imaging: Claustrophobia or Pacemaker or other implanted metal device

Small number of patients who completed the study. Overall underpowered.