Efficacy of bucindolol in systemic hypertension

Bucindolol displays intrinsic sympathomimetic activity in human myocardium

BACKGROUND

Most clinical studies have shown that beta-adrenergic receptor antagonists improve long-term survival in heart failure patients. Bucindolol, a nonselective beta-receptor blocker, however, failed to reduce heart failure mortality in a recent large clinical trial. The reasons for this failure are not known. Bucindolol has partial agonist properties in rat myocardium, but whether it has agonist activity in human heart is controversial. To address this, we measured the ability of bucindolol to increase cAMP accumulation in human myocardium.

METHODS AND RESULTS

Myocardial strips ( approximately 1 mm(3)) obtained from rat and nonfailing human hearts were confirmed to be viable for > or = 48 hours in normoxic tissue culture by MTT assay and histology. Freshly isolated strips were exposed to beta-adrenergic antagonists and agonists and assayed for cAMP. In both rat and human strips, the full beta-adrenergic agonist isoproterenol raised cAMP levels by >2.5-fold at 15 minutes. Carvedilol and propranolol had no effect on basal cAMP levels, whereas metoprolol reduced basal cAMP by approximately 25%. In contrast, bucindolol and xamoterol increased cAMP levels in a concentration-dependent manner in both rat and human myocardium (maximum 1.64+/-0.25-fold and 2.00+/-0.27-fold over control, respectively, P<0.01 for human tissue).

CONCLUSIONS

Bucindolol exhibits approximately 60% of the beta-adrenergic agonist activity of xamoterol in normal human myocardial tissue.

Long-term beta-blocker vasodilator therapy improves cardiac function in idiopathic dilated cardiomyopathy: a double-blind, randomized study of bucindolol versus placebo

PURPOSE

Bucindolol is a potent nonselective beta-blocking agent with vasodilatory properties. In this study, we evaluated the effects of long-term bucindolol therapy in the treatment of heart failure from idiopathic dilated cardiomyopathy.

PATIENTS AND METHODS

Patients were eligible for enrollment if they had symptomatic heart failure, idiopathic dilated cardiomyopathy, and left ventricular ejection fraction less than 0.40. All patients received an initial test dose of 12.5 mg bucindolol orally every 12 hours for two or three doses. Patients tolerating the test dose were randomly assigned (double-blind) to receive bucindolol or placebo in a 3:2 ratio. Study medication was begun at a dose of 12.5 mg orally every 12 hours and gradually increased over a 1-month period until either a maximum tolerated dose or a target dose of 100 mg every 12 hours was reached. Study medication was then continued for an additional 2 months.

RESULTS

A total of 24 patients were enrolled into the study. Twenty-three patients tolerated bucindolol test challenge; 14 were randomized to receive bucindolol, and nine were randomly assigned to receive placebo. The placebo group (age 56 +/- 2 years) was significantly older than the bucindolol group (46 +/- 3 years), but by all other clinical and hemodynamic parameters the two groups were comparable. Twenty-two of 23 patients completed the study. Patients treated with bucindolol had significant improvements in clinical heart failure symptoms and in resting hemodynamic function, including an increase of left ventricular ejection fraction (0.26 +/- 0.02 to 0.35 +/- 0.09, p = 0.003), cardiac index (2.2 +/- 0.1 to 2.5 +/- 0.4 L/minute/m2, p = 0.014), and left ventricular stroke work index (25 +/- 3 to 35 +/- 7 g.m/m2, p = 0.002) and a decrease in pulmonary artery wedge pressure (17 +/- 3 to 10 +/- 5 mm Hg, p = 0.005) and heart rate (86 +/- 3 to 75 +/- 9 beats/minute, p = 0.012). Patients treated with bucindolol also had a significant increase in exercise left ventricular ejection fraction (0.26 +/- 0.03 to 0.32 +/- 0.14, p = 0.015) and reduction in questionnaire-measured symptoms (p = 0.007) and New York Heart Association functional class (p less than 0.001). However, total treadmill exercise duration and maximal oxygen consumption with exercise did not change. No changes in rest or exercise parameters were observed in the placebo-treated group. Central venous plasma norepinephrine concentration decreased significantly in the bucindolol-treated group (423 +/- 79 to 212 +/- 101 pg/mL, p = 0.010), but was unchanged in the placebo-treated group.

CONCLUSION

Bucindolol is well tolerated in patients with idiopathic dilated cardiomyopathy and congestive heart failure, and therapy for 3 months is associated with improved resting cardiac function, improved heart failure symptoms, and a reduction in venous norepinephrine concentration.

Effects of celiprolol on plasma renin, aldosterone, norepinephrine and epinephrine in primary hypertension

Celiprolol is a newly developed cardioselective beta-blocking agent with mild beta 2-agonist and weak alpha 2-antagonist properties. To evaluate the acute (2.5 hours) and chronic (2 weeks) effects of celiprolol (400 mg once a day) on plasma renin, aldosterone, norepinephrine and epinephrine, 20 patients with mild to moderate primary hypertension were studied in a double-blind placebo-controlled crossover trial. Two and one-half hours after the first dose of both placebo and celiprolol, supine and standing measurements of blood pressure showed a significant reduction, whereas plasma norepinephrine increases were comparable with baseline values. Placebo and celiprolol produced similar changes on supine blood pressure and plasma norepinephrine. In 9 patients celiprolol decreased plasma renin (from a mean +/- standard deviation of 1.09 +/- 0.35 to 0.77 +/- 0.52 ng/ml/hr, p less than 0.05) and aldosterone (from 9.2 +/- 3.7 to 6.7 +/- 3.9 ng/dl, p less than 0.05) acutely both supine and standing, but placebo did not change these parameters. Celiprolol increased pulse rate supine (but not standing) as compared with baseline values. After 2 weeks of celiprolol therapy, blood pressure was decreased both supine and standing compared with placebo in 18 patients (140 +/- 18/88 +/- 8 vs 149 +/- 18/94 +/- 7, 136 +/- 18/91 +/- 6 vs 142 +/- 20/97 +/- 9 mm Hg, respectively, each p less than 0.05), without a change of pulse rate when supine and with a reduction when standing. There were no significant changes of plasma renin, aldosterone, norepinephrine and epinephrine levels during chronic therapy compared with placebo.

Progress in antihypertensive therapy with a multiple-action drug

The beta-blockers in clinical use have been classified into 2 major divisions, nonselective or selective agents, and those with or without intrinsic sympathomimetic activity (ISA). These properties confer differing pharmacological properties with some relevance to the treatment of hypertension. A beta-blocker with significant beta 2-ISA can be regarded as a multiple-action drug. A third division of beta-blockers is a newer development; these agents, besides blocking the beta-receptor, possess important peripheral vasodilator activity. Labetalol was the first drug of this group and prizidolol followed, but has been withdrawn because of toxicity. Several other agents now under evaluation include bucindolol and medroxolol, and carvedilol and dilevalol (1 of the isomers of labetalol), which have been the most widely studied in hypertension. Combined action results in important haemodynamic differences compared with pure beta-blockade. Notably, peripheral resistance is reduced, and there is less reduction in, or no effect on, cardiac output. The 3 following mechanisms have been described as responsible for peripheral vasodilatation: alpha-receptor blockade, beta 2-agonism, and a dilator action independent of either the alpha- or beta-receptors. Evidence for these various mechanisms is more readily obtainable from animal experiments, but some confirmatory evidence has been obtained in man. Inhibition of alpha-stimulation has been found with labetalol and to a small degree with medroxalol and carvedilol. beta 2-Mediated vasodilatation has been shown by dilevalol and medroxolol, and evidence of vasodilatation independent of alpha- or beta-receptors has been obtained with carvedilol. More evidence is required to confirm the exact contribution of each of these mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)