Role of the α‐Receptor in the Control of Noradrenaline Release from Sympathetic Nerves

Phenoxybenzamine, hydergin and phentolamine, all markedly increased the overflow of 3H‐nor‐adrenaline in response to transmural stimulation of the guinea pig vas deferens. After phannacological blockade of neuronal and extraneuronal uptake of noradrenaline, and after inhibition of local prostaglandin formation, the three compounds were still effective and caused increased overflow of 3H‐noradrenaline. This effect was abolished by prostaglandin E2. Using the same pharmacological blockade, noradrenaline and methoxamine inhibited stimulated overflow of “H‐noradrenaline in a dose‐dependent manner. It is concluded that the activity of α‐receptors Per se can feed back regulate the release of noradrenaline from sympathetic nerves. The possibility that the receptors are presynaptically located and that they act on Ca++ influx into the neuron is discussed.