Inhibition of the alpha 1 and alpha 2-adrenoceptor-mediated pressor response in pithed rats by raubasine, tetrahydroalstonine and akuammigine.

The relative potencies of raubasine, tetrahydroalstonine (THA) and akuammigine on alpha 1- and alpha 2-adrenoceptors were assessed by comparing their effects on the rise in blood pressure induced by stimulation of the sympathetic outflow from the spinal cord or by injection of noradrenaline in pithed rats. Akuammigine was inactive in both cases. Raubasine preferentially antagonized the effects of electrical stimulation while THA antagonized the effects of injected noradrenaline. The results suggest that raubasine preferentially blocks alpha 1-adrenoceptors while THA is more selective for alpha 2-adrenoceptors.