Cardiovascular effects of acebutolol and hydrochlorothiazide in essential hypertension

Effects of celiprolol on systemic and forearm circulation in hypertensive patients: a double-blind cross-over study versus metoprolol

The antihypertensive efficacy of a new beta-receptor blocking agent, celiprolol, was compared with that of a well-established antihypertensive drug, metoprolol. Their systemic and forearm hemodynamic effects were investigated using echocardiography and two-dimensional pulsed Doppler flowmetry, respectively. Twenty hypertensive patients completed a double-blind, cross-over, randomized study using celiprolol and metoprolol. Two six-week courses with celiprolol or metoprolol were preceded and followed by a two-week placebo period; the total duration of the study was 18 weeks. In spite of a comparable efficacy in reducing systolic and diastolic blood pressure (about 10% of the basal value), the two drugs showed quite different systemic and regional hemodynamic effects. Celiprolol induced a significant decrease in forearm vascular resistance (from 157 +/- 17 to 113 +/- 13 mm Hg/mL/s, P less than .01) and total peripheral resistance (from 1596 +/- 90 to 1398 +/- 91 dyne.s.cm-5, P less than .05) whereas cardiac output remained unchanged and forearm blood flow increased. Metoprolol reduced cardiac output (from 6.5 +/- 3 to 5.7 +/- 3 L/min, P less than .05), through a reduction in heart rate, since stroke volume was unchanged. Both drugs did not significantly modify cardiac performance, as evaluated by left ventricle fractional shortening and ejection fraction. Thus, the two drugs seem to reduce blood pressure through different hemodynamic mechanisms.

Inhibitory effect of frusemide on sympathetic vasoconstrictor responses: dependence on a renal hormone and the vascular endothelium

1. Mesenteric perfusion pressure was measured in the in situ mesentery perfused at a constant rate with blood drawn from the carotid artery of the same anaesthetized rat. Increases in perfusion pressure were produced by mesenteric periarterial electrical stimulation. These responses were measured before and 30 min after the administration of frusemide (5 mg/kg i.v.) to the rat. Loss of volume due to the frusemide-induced diuresis was prevented by a urinary bladder-venous extracorporeal circuit. 2. Responses to stimulation were reduced after frusemide and were not increased by the subsequent administration of indomethacin (2 mg/kg i.v.). This indomethacin treatment rapidly and completely prevented the fall in blood pressure produced by i.v. arachidonic acid. 3. In rats where the renal papilla had been ablated by treatment with bromoethylamine (200 mg/kg i.p.) 5 weeks previously, frusemide administration did not reduce sympathetic responses in the in situ blood-perfused mesentery. 4. A segment of rat tail artery, cannulated at both ends was mounted in an organ bath and perfused with blood withdrawn from, and returned to, an anaesthetized rat. Increases in perfusion pressure produced by periarterial electrical stimulation of this ex vivo blood perfused tail artery segment were reduced by frusemide administration to the anaesthetized rat. 5. When the endothelium was removed from the tail artery segment, frusemide administration did not lead to any reduction of vasoconstrictor responses. 6. Frusemide may lead to the release of a non-prostanoid hormone from the renal medulla which results in inhibition of peripheral sympathetic vasoconstrictor responses. The release of the hormone may involve intra-renal prostaglandins. The final antivasoconstrictor effect requires an intact vascular endothelium.

Acebutolol: a review of its pharmacology, pharmacokinetics, clinical uses, and adverse effects

Acebutolol is a new hydrophilic, cardioselective beta-adrenergic-blocking agent that possesses partial agonist and membrane-stabilizing activities. In the treatment of mild to moderate essential hypertension, once-daily acebutolol as monotherapy provides effective control in a large majority of patients and produces a further reduction in blood pressure when used concomitantly with diuretics. Acebutolol is as effective as other beta-blocking agents, and in a large, double-blind, parallel study against propranolol was found to cause less reduction in heart rate, and fewer neurologic side effects and patient withdrawals due to adverse effects. Oral acebutolol is also effective in suppressing premature ventricular contractions, and in small numbers of patients generally beneficial results were obtained in supraventricular and ventricular arrhythmias with intravenous administration. These salutary effects are attributable to beta blockade. Controlled clinical trials documented the antianginal actions of oral acebutolol in chronic stable angina pectoris; its efficacy in this regard is comparable to that of other beta-blocking agents. The drug produces smaller decreases in heart rate and cardiac output and alterations in peripheral vascular hemodynamics than beta-blocking drugs without partial agonist activity, and because of its cardioselectivity, it may be used cautiously in patients with bronchospastic disease. Acebutolol has minimal metabolic effects and does not elevate levels of blood lipids during long-term therapy; high-density-lipoprotein cholesterol increased with acebutolol in a small number of patients.

Acebutolol: ten years of experience

During 10 years of clinical use involving almost 3 million patient-years, acebutolol has become established as a remarkably safe and well-tolerated beta-blocking agent, effective in treating essential hypertension and cardiac arrhythmias. The existence of a long-lived active metabolite (diacetolol) confers a 24-hour duration of action, which permits effective use of a once-daily regimen, particularly for hypertension. Acebutolol has low lipid solubility and low protein binding; the former property reduces the risk of central side effects, and the latter means that displacement interactions with other drugs are unlikely. Because acebutolol and its metabolite normally have both renal and hepatic excretion pathways, an alternative pathway is available should either be compromised through disease. Acebutolol is cardioselective, and clinical use has borne out the low incidence of bronchospasm in patients with impaired lung function. The possession of intrinsic sympathomimetic activity (ISA) leads to only modest reductions in cardiac output, which in turn reduces the chance of excessive bradycardia and the likelihood of precipitating heart failure. A combination of selectivity and ISA may be responsible for the low incidence of tiredness and cold extremities observed with acebutolol compared with other beta blockers. The unique pharmacologic and pharmacokinetic profile of acebutolol confers several therapeutic advantages and may be responsible for the generally low level of side effects experienced in clinical use.

The lowering of daytime blood pressures with a single daily dose of acebutolol in ambulant hypertensives

Intra-arterial blood pressure recordings were studied in 10 ambulant subjects with essential hypertension to evaluate the effect of a single daily dose of acebutolol. Blood pressures and heart rates, measured on a beat-to-beat basis were averaged over every hour, for the daytime, night-time, and for the total 24 hours. Acebutolol significantly lowered the average daytime systolic pressure (160 to 142 mmHg, p = less than 0.01), diastolic pressure (78 to 66 mmHg, p = less than 0.01), and the heart rate (92 to 77 beats/min, p = less than 0.001). Significantly lower pressures were demonstrated up to 11 hours after the last dose of acebutolol. The effect on heart rate lasted up to 13 hours. The observed lowering of pressures and heart rate during the remaining 11 hours did not reach statistical significance.

Peripheral hemodynamic effects of short-term nadolol administration in essential hypertension

A study of forearm arterial and venous hemodynamics by pulsed Doppler velocimetry and plethysmography was performed in 21 patients with essential hypertension, aged 16 to 54 years, before and after short-term nadolol administration at a dose of 0.05 mg/kg. Because of a large intersubject variability in the responses of the hemodynamic parameters to nadolol, an unconventional statistic approach was used to divide the overall population of patients into two homogeneous groups. The first included nine patients (group 1) and the second 12 patients (group 2). In patients of group 1, nadolol significantly decreased the systolic blood pressure (p less than 0.001), venous tone (p less than 0.01), and brachial artery flow (p less than 0.05). In patients of group 2, nadolol did not affect any forearm parameters. Each group of patients was compared to an age- and pressure-matched group of patients receiving propranolol at equiblocking doses. Contrary to nadolol, propranolol was found to increase significantly the forearm vascular resistance in patients of groups 1 and 2 (90 +/- 19%, p less than 0.001; 63 +/- 10%, p less than 0.001, respectively). Thus the hemodynamic beta-blocking effects of nadolol in the forearm were less marked than those of propranolol, suggesting that the effects of acute beta blockade by nadolol could be offset by other effects, such as a peripheral partial-agonist effect.

Effect of acebutolol on left ventricular hemodynamics and anatomy in systemic hypertension

In 18 patients with mild or moderate essential hypertension who responded favorably to acebutolol antihypertensive therapy, echocardiography (echo) was performed in the basal condition and after 6 and 12 months of follow-up. Acebutolol induced a significant decrease in blood pressure (BP), from a basal value of 167 +/- 3/105 +/- 2 mm Hg to 138 +/- 5/90 +/- 2 mm Hg after 6 months (p less than 0.01) and to 134 +/- 3/91 +/- 3 mm Hg after 1 year (p less than 0.01), and in heart rate, from 75 +/- 3 to 63 +/- 2 beats/min after 6 months (p less than 0.01) and to 63 +/- 2 beats/min after 1 year (p less than 0.01). The decrease in BP was achieved through a decrease in cardiac output from 6.3 +/- 0.28 to 5.3 +/- 0.25 liters/min after 6 months (p less than 0.05) and to 5.32 +/- 0.2 liters/min after 1 year (p less than 0.05), which resulted from a reduction in heart rate; stroke volume did not show significant change during the treatment and left ventricular (LV) performance was improved. There was a parallel decrease in LV posterior wall and ventricular septal thicknesses and estimated LV mass. In patients with LV hypertrophy, the change in mass was significantly correlated with the change in heart rate both after 6 and 12 months of therapy (r = 0.6234, p less than 0.05 and r = 0.7121, p less than 0.05 after 6 and 12 months, respectively).

Diuretic treatment in essential hypertension

In North America, diuretics remain the most common first-line drug therapy for essential hypertension based on efficacy, safety and cost. The promotion of step-care programmes has firmly established their dominant use on this continent whereas in Europe, particularly in Scandinavia and Great Britain, beta-adrenoceptor blocking agents are more frequently chosen as first-line therapy. On both continents, combined therapy with a diuretic and a beta-blocker is probably the most common second step for patients with blood pressures uncontrolled on a single agent alone and diuretics remain useful, if not essential, to prevent sodium retention commonly observed with other antihypertensive agents. Although the forced loss of sodium and water may be responsible for their initial antihypertensive effect, the mechanism underlying their long-term effect is unknown but probably involves some alteration of vascular smooth muscle reactivity. More recently, concern has been expressed about their long-term safety as larger populations are being exposed to diuretic agents for a significant proportion of their life-span. These concerns include haemodynamic and biochemical consequences of diuretic therapy - excessive tachycardia at rest and with minimal exercise, postural hypotension, hypokalaemia and arrhythmias, muscle cramps or fatigue, glucose intolerance, hyperuricaemia and altered circulating lipids as markers or promotors of atherosclerosis and its complications. At present, there is insufficient evidence to alter the present recommendation of diuretic agents as first-line drug therapy in the treatment of hypertension.