Vascular alpha-adrenergic blocking properties of quinidine.

The specificity of the alpha-adrenergic vascular blockade by quinidine was tested in the intact dog, in rabbit isolated aortic strips, and in rats under ganglionic blockade. Quinidine did not affect the pressor response of angiotensin II in dogs, the contractile response of histamine nor angiotensin II in aortic strips, nor the dose-pressor response curve of the alpha-agonist, B-HT 933 in the rat. However, the pressor effect of adrenaline and noradrenaline (NA) were significantly reduced in dogs, and the dose-response curves to NA in aortic strips and to the alpha-agonist, phenylephrine in rats was shifted to the right in a parallel manner by quinidine. In the rat, quinidine is at least 14 times more potent in antagonizing the vasopressor effect of an alpha 1-vs. and alpha 2-adrenoceptor agonist.