INFLUENCE OF PROPRANOLOL AND ICI 50,172 ON THE CARDIOVASCULAR ACTIONS OF CATECHOLAMINES AS MODIFIED BY ERGOTAMINE

¹ Laboratório de Farmacologia, Faculdade de Medicina, Porto, Portugal

The action of ergotamine on several responses of the anesthetized dog (blood pressure, heart rate, heart contractile force, peripheral blood flow, perfusion pressure of the hind limb and contractions of the retractor penis) to epinephrine and isoproterenol were evaluated. Whereas ergotamine neither stimulated nor blocked beta receptors, it blocked the alpha receptors of the peripheral vasculature and of the retractor penis in doses which did not cause a reduction in the pressor response to epinephrine but induced reversal of isoproterenol. The pressor responses to epinephrine and isoproterenol after ergotamine were prevented or antagonized by the beta blocking drugs propranolol and ICI 50,172. It is concluded that at least two factors are involved in the elicitation of preasor responses to epinephrine and isoproterenol after ergotamine, namely, the unaffected cardiostimulant action of the amines and the reduction in the capacity of the vascular bed caused by ergotamine.