[The specificity of action of penbutolol and propranolol and their optical isomers].

Several specific and unspecific effects of penbutolol and propranolol and their optical isomers were tested in the following test models: -- The beta-sympatholytic activity in the heart of the anaesthetized dog (measurement of the contractility), -- the sympathomimetic intrinsic activity in the reserpinized rat, -- the antiarrhythmic activity in the digoxin poisoned guinea pig, the digitoxin/aconitine poisoned isolated guinea pig heart, and the cooled cat, -- the beta-sympatholytic activity together with electrophysiological effects in the isolated guinea pig papillary muscle. The antiarrhythmic effects of l-penbutolol are mainly due to its beta-sympatholytic activity. d-Penbutolol reveals only a local anaesthetic action and is otherwise nearly without pharmacological effects. In beta-sympatholysis it is 50 times less active than l-penbutolol. It has no intrinsic sympathomimetic activity. It does not prolong the refractory period in the heart muscle. For this reason only l-penbutolol is proposed to be used as a beta-sympatholytic drug.