Adrenergic neuron blocking properties of (±)-propranolol and (+)-propranolol

The action of (±)-propranolol and (+)-propranolol on the electrical stimulation of adrenergic nerves to smooth muscle has been studied in the isolated ear artery from rabbits and the isolated vas deferens preparation from rats. Both drugs exhibited an adrenergic neuron blocking action at a pre-junctional site at concentrations ranging from 4·6 to 14 μg/ml. At lower concentrations the effects were variable and more often potentiation of the responses was observed. The responses to added noradrenaline were uniformly potentiated. The effect was related to local anaesthetic activity and not considered to be a specific adrenergic neuron blocking effect as occurs with guanethidine or bretylium.