Effects of the calcium antagonist felodipine on the sympathetic and renin-angiotensin-aldosterone systems in essential hypertension

Effect of calcium antagonists on plasma norepinephrine levels, heart rate, and blood pressure

To evaluate the effects of calcium antagonists on sympathetic activity in hypertensive patients, a MEDLINE search for English language articles published between 1975 and May 1996 using the terms calcium antagonists, sympathetic nervous system, and catecholamines was conducted. Clinical studies only reporting the effects of calcium antagonists on blood pressure, heart rate, and plasma norepinephrine (NE) levels in patients with hypertension were included. Data were combined and analyzed according to class of calcium antagonist (dihydropyridine vs nondihydropyridine), their duration of action (short-acting [SA] vs long-acting [LA]), and treatment duration. We identified 63 studies involving 1,252 patients. Acutely after single dosing, SA calcium antagonists decreased mean arterial pressure by 13.7 +/- 1.1% and increased heart rate by 13.7 +/- 1.4% and NE levels by 28.6 +/- 2.5%. Change in NE levels correlated with change in heart rate (r = 0.59, p <0.01) and inversely with change in arterial pressure (r = 0.46, p <0.05) in patients taking dihydropyridine calcium antagonists acutely. With sustained therapy, both classes of SA calcium antagonists increased NE levels. Whereas NE levels remained slightly elevated and heart rate unchanged with LA dihydropyridine calcium antagonists, both heart rate and NE levels decreased with LA nondihydropyridine calcium antagonists. SA calcium antagonists stimulate sympathetic activity when given acutely and over the long term, irrespective of their molecular structure. Sympathetic activation is less pronounced with LA dihydropyridine calcium antagonists and decreases with LA nondihydropyridine calcium antagonists. These data offer a possible pathophysiologic explanation for the increase in morbidity and mortality observed in some studies using SA calcium antagonists.

Effects of felodipine, metoprolol and their combination on blood pressure at rest and during exercise and on volume regulatory hormones in hypertensive patients

The effects on blood pressure (BP) and heart rate (HR), at rest and during bicycle exercise, of the vascular selective calcium antagonist felodipine, the cardio-selective beta-blocker metoprolol, and of the two drugs in combination, were assessed in a double-blind, three-way cross-over study comprising 23 patients with essential, mild to moderate hypertension. All three treatment regimens were given to each patient in randomised order for 4 weeks after a 4 week placebo run-in period. Felodipine 10-20 mg daily, metoprolol 100-200 mg daily and the combination of felodipine 10-20 mg plus metoprolol 100 mg daily were all effective antihypertensive treatments both at rest and during exercise. The two drugs seemed to have additive effects and the effect on BP of the combination was greater than that of either drug given as monotherapy. The mean sitting BP was 148/103 mmHg at randomisation, after 4 weeks of placebo treatment, and 134/88, 134/94 and 121/84 mmHg, respectively, after 4 weeks' treatment with felodipine, metoprolol and the combination. Maximal exercise capacity was similar irrespective of treatment regimen, and the normal response to exercise BP and HR was maintained during all active treatments. Changes observed in volume regulatory hormones (PRA, aldosterone and ANP) were consistent with a direct tubular natriuretic-diuretic effect of felodipine and of beta-blocker attenuated release of renin. All treatment regimens were well tolerated and adverse events reported were usually mild and transient.

Acute and chronic calcium antagonist treatment elevates sympathetic activity in primary hypertension

Eleven men with mild to moderate primary hypertension were studied at rest and during mental stress before and during intravenous infusion of the calcium antagonist felodipine. Eight of them were restudied during long-term treatment (extended-release felodipine, 10 mg daily). For comparison, 10 normotensive control subjects were studied with the short-term protocol. Heart rate, cardiac output, central cardiovascular pressures, and forearm blood flow were registered. Arterial and venous sampling was performed. Norepinephrine spillovers to arterial plasma and from the forearm were assessed with the use of radiotracer methodology. In the hypertensive patients, felodipine lowered mean arterial blood pressure acutely by 8% (P < .01). Systemic vascular resistance decreased by 22% (P < .001), cardiac output increased by 20% (P < .01), and norepinephrine spillover to arterial plasma increased by 61% (P < .001). Forearm vascular resistance fell by 30% (P < .001), but norepinephrine overflow from the forearm increased by 115% (P < .001). These forearm responses were not seen in normotensive subjects despite similar systemic responses to felodipine infusion. After 8 weeks of treatment, mean arterial pressure decreased to 15% below baseline (P < .001), cardiac output returned toward pretreatment levels, and systemic vascular resistance remained low. Forearm blood flow returned toward basal levels, but forearm vascular resistance remained lowered. Total body and forearm norepinephrine spillover values were as elevated as in the acute situation. The hemodynamic "defense reaction" and the sympathoadrenal response to mental stress were essentially unaffected by felodipine. Stress-induced small elevations of neuropeptide Y-like immunoreactivity persisted during felodipine. Thus, the vasodilatation induced by felodipine elicits sympathetic counterregulation, which persists in the long term with respect to peripheral and total sympathetic activities, despite resetting of the baroreflex control of heart rate.

Felodipine: a new dihydropyridine calcium-channel antagonist

Felodipine, a dihydropyridine calcium-channel antagonist, significantly reduces systolic and diastolic blood pressure (BP) in patients with hypertension and has been associated with beneficial hemodynamic effects in patients with chronic stable angina pectoris or congestive heart failure (CHF). In hypertensive patients, felodipine does not appear to significantly affect glomerular filtration rate, creatinine clearance, glucose tolerance, or plasma lipoprotein concentrations. Studies comparing felodipine with other agents as monotherapy in mild to moderate hypertension have demonstrated felodipine to be at least as efficacious as hydrochlorothiazide (HCTZ) and HCTZ plus amiloride hydrochloride in combination. Comparisons of felodipine with other agents as adjuncts to beta-blocker or diuretic therapy have shown felodipine to be at least as effective as HCTZ, propranolol hydrochloride, prazosin hydrochloride, and nifedipine. Evaluations of patients with chronic stable angina are limited, and additional studies are needed before felodipine can be recommended for the routine management of angina pectoris. Similarly, additional studies are essential to delineate the role of felodipine, if any, in the management of CHF. In the management of hypertension, felodipine 5-40 mg/d significantly reduces systolic and diastolic BP. Although some patients may be controlled throughout the entire dosing interval when felodipine is administered bid, many patients will require more frequent dosing to obtain adequate BP control. Adverse effects associated with felodipine are similar to those of other dihydropyridine calcium-channel antagonists and include peripheral edema, headache, dizziness, flushing, and fatigue. A potentially clinically important drug interaction was observed when felodipine was administered concomitantly with theophylline aminopropanol; significant decreases in theophylline concentrations were noted. In summary, felodipine appears to be safe and effective for the management of hypertension when used alone or in combination with other antihypertensive agents. The efficacy of felodipine in the management of chronic stable angina pectoris and CHF requires further investigation.

Carotid artery surgery. Local versus general anaesthesia as related to sympathetic activity and cardiovascular effects

Arterial plasma catecholamines, blood pressure and heart rate were determined in 75 patients before, during and after carotid endarterectomy. Local anaesthesia given as a cervical block with skin infiltration containing 200 micrograms adrenaline was used in 28 patients (LA-group), general anaesthesia (nitrous oxide, fentanyl, isoflurane) with skin infiltration containing 200 micrograms adrenaline in 32 patients (GAs-group) and general anaesthesia without skin infiltration in 15 patients (GAo-group). In the LA-Group plasma noradrenaline (P-NA) levels were significantly higher during anaesthesia and surgery, with an increase from preanaesthesia levels (P less than 0.05). P-NA decreased from a preanaesthesia level in the GAo-group (P less than 0.01) but remained unaltered in the GAs-group. P-NA values in the GAo-group were lower than those of the GAs-group (P less than 0.001) following anaesthesia and surgery. Plasma adrenaline (P-A) increased in the LA- and the GAs-group and decreased in the GAo-group (P less than 0.001) following anaesthesia and surgery. In the LA-group P-A was similar before the skin incision and clamping but higher after declamping as compared to the GAs-group. Before the skin incision and thereafter P-A was lower in the GAo-group as compared to the other groups. There was a positive correlation between plasma catecholamines, on the one hand, and mean blood pressure and heart rate on the other. Two patients in the LA-, eight in the GAs- and seven in the GAo-group showed a hypotensive blood pressure reaction (SBP less than 100 mmHg; LA vs. GAo, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)