Beta-adrenergic blocking effects and cardiodepressant activity of penbutolol and its two optical isomers in the guinea-pig left atrium.

The beta-adrenoceptor blocking potency and cardiodepressant activity of penbutolol and its two isomers have been evaluated in the guinea-pig left atrium in order to determine if the two properties are related. While (-)-penbutolol was ten times more potent than (+)-penbutolol and three times more potent than (+/-)-penbutolol as a beta-adrenoceptor antagonist, the three compounds showed a similar activity as cardiodepressant agents. These results seem to demonstrate that it is unlikely that this depressant action can be related to the antagonism of beta adrenoceptors.