Alprenolol hydrochloride

The selectivity of beta-adrenoceptor antagonists at the human beta1, beta2 and beta3 adrenoceptors.[Pubmed:15655528]

Br J Pharmacol. 2005 Feb;144(3):317-22.

Beta-adrenoceptor antagonists ("beta-blockers") are one of the most widely used classes of drugs in cardiovascular medicine (hypertension, ischaemic heart disease and increasingly in heart failure) as well as in the management of anxiety, migraine and glaucoma. Where known, the mode of action in cardiovascular disease is from antagonism of endogenous catecholamine responses in the heart (mainly at beta1-adrenoceptors), while the worrisome side effects of bronchospasm result from airway beta2-adrenoceptor blockade. The aim of this study was to determine the selectivity of beta-antagonists for the human beta-adrenoceptor subtypes. (3)H-CGP 12177 whole cell-binding studies were undertaken in CHO cell lines stably expressing either the human beta1-, beta2- or the beta3-adrenoceptor in order to determine the affinity of ligands for each receptor subtype in the same cell background. In this study, the selectivity of well-known subtype-selective ligands was clearly demonstrated: thus, the selective beta1 antagonist CGP 20712A was 501-fold selective over beta2 and 4169-fold selective over beta3; the beta2-selective antagonist ICI 118551 was 550- and 661-fold selective over beta1 and beta3, respectively, and the selective beta3 compound CL 316243 was 10-fold selective over beta2 and more than 129-fold selective over beta1. Those beta2-adrenoceptor agonists used clinically for the treatment of asthma and COPD were beta2 selective: 29-, 61- and 2818-fold for salbutamol, terbutaline and salmeterol over beta1, respectively. There was little difference in the affinity of these ligands between beta1 and beta3 adrenoceptors. The clinically used beta-antagonists studied ranged from bisoprolol (14-fold beta1-selective) to timolol (26-fold beta2-selective). However, the majority showed little selectivity for the beta1- over the beta2-adrenoceptor, with many actually being more beta2-selective. This study shows that the beta1/beta2 selectivity of most clinically used beta-blockers is poor in intact cells, and that some compounds that are traditionally classed as "beta1-selective" actually have higher affinity for the beta2-adrenoceptor. There is therefore considerable potential for developing more selective beta-antagonists for clinical use and thereby reducing the side-effect profile of beta-blockers.

The 5-HT1A antagonist (-)-alprenolol fails to modify sleep or zimeldine-induced sleep-waking effects in rats.[Pubmed:1388278]

Pharmacol Biochem Behav. 1992 May;42(1):49-56.

Sleep and waking in rats were studied for 8 h following administration of a selective 5-hydroxytryptamine (5-HT) reuptake inhibitor (zimeldine), a putative 5-HT1A antagonist (L(-)-alprenolol hydrogene tartrate monohydrate [(-)-alprenolol]) and a combination of (-)-alprenolol and zimeldine. Consistent with earlier findings, zimeldine gave a biphasic effect on sleep and waking. Waking was increased during the first 3 h, followed by a small decrease. Deep slow-wave sleep (SWS-2) showed the opposite trend. An initial decrease in SWS-2 was followed by an increase after around 3 h. Rapid eye movement sleep was markedly suppressed and latencies to sleep increased after zimeldine. (-)-Alprenolol had no effects on the different sleep and waking stages or latencies to sleep. The 5-HT1A antagonist also failed to modify the effects of zimeldine administration. The behavioral syndrome induced by a selective 5-HT1A agonist [8-hydroxy-2-(di-n-propyl-amino)-tetralin (8-OH-DPAT)] was clearly antagonized by administration of (-)-alprenolol, indicating that (-)-alprenolol was an efficient 5-HT1A blocker. The data indicate that the sleep-waking effects of zimeldine cannot easily be explained by stimulation of 5-HT1A receptors.

Antagonist characterization of atypical beta adrenoceptors in guinea pig ileum: blockade by alprenolol and dihydroalprenolol.[Pubmed:1969469]

J Pharmacol Exp Ther. 1990 Mar;252(3):1034-42.

The present study was undertaken to further characterize the atypical beta adrenoceptor in guinea pig ileum. Tension was developed in isolated segments of ileum using transmural electrical stimulation of enteric cholingeric nerves. The ability of isoproterenol to relax the ileum, via beta-1 adrenoceptor and atypical beta adrenoceptor agonism, was measured. Propranolol (5 x 10(-6) M) and bromoacetylaprenololmetane blocked beta-1 adrenoceptors but, at the concentrations tested, were without affinity at atypical beta adrenoceptors. (-)-Alprenolol and (-)-dihydroalprenolol, however, acted as competitive antagonists at both sites (pA2 values of 8.2 and 8.81 at beta-1 adrenoceptors and 6.47 and 6.43 at atypical beta adrenoceptors, respectively). (-)-Alprenolol also exerted agonistic activity at the atypical beta adrenoceptor. [3H](-)-Dihydroproalprenolol failed to identify beta-1 adrenoceptors or atypical beta adrenoceptors but, instead, bound to a putative lipophilic site unrelated to ileal adrenoceptors. Before this study, nadolol (pA2 = 4.7) was the only documented antagonist at the atypical beta adrenoceptor in guinea pig ileum. Thus, the present results detail two additional pharmacological probes which exhibit about a 100-fold greater affinity than nadolol for the atypical site.