Effect of disopyramide on isolated aortic ring of the rat

Disopyramide produces a contraction of the isolated aortic ring of the rat which is graded, develops slowly, and has a time course similar to the tonic phase of the noradrenaline response. This effect is not modified by alpha-adrenoceptor blockade (yohimbine) but is completely abolished by a Ca2+ antagonist (verapamil) or by removal of Ca2+ from the bathing solution. These results indicate that, in the rat aorta, disopyramide has a vasoconstrictor effect dependent on Ca2+ influx across the vascular smooth muscle membrane.