Catecholamines and the renin-angiotensin-aldosterone system during treatment with felodipine ER or hydrochlorothiazide in essential hypertension.

The neurohumoral responses after 10 mg of felodipine extended release (ER), a new dihydropyridine calcium antagonist, and 25 mg of hydrochlorothiazide (HCTZ) were compared in a randomized, double-blind, crossover trial in 28 mild to moderate hypertensives. Antihypertensive drugs were gradually discontinued. Felodipine ER, 10 mg was given once daily for 2 weeks; after another washout period of 1 week, patients were switched to 25 mg of HCTZ once daily and vice versa. Blood pressure (BP) was measured at baseline, 2.5 h after medication, and after 2 weeks of treatment (24 h postdosing) using an oscillometric device. Felodipine ER and HCTZ both lowered BP effectively. However, felodipine ER was superior in reducing systolic and diastolic BP during the short term and medium term. Treatment with felodipine ER over 2 weeks increased sympathetic outflow as indicated by elevated plasma norepinephrine levels, whereas plasma epinephrine was mainly unaffected, as were plasma renin and aldosterone levels. On the other hand, 25 mg of HCTZ increased plasma renin and aldosterone, but left catecholamines unchanged. Despite persistent increased sympathetic activity, the reduction in BP in this study was more pronounced after felodipine ER as compared to HCTZ. The lack of a difference between heart rates under both medications after 2 weeks of treatment suggests a resetting of the baroreflex by felodipine ER and furthermore that the increased norepinephrine levels may not be clinically relevant, but demonstrate the maintained baroreflex activity. HCTZ, in doses as low as 25 mg, is still capable of stimulating the renin-angiotensin-aldosterone system.