Paradoxical Relaxation of Arterial Strips Induced by Vasoconstrictive Agents

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Abstract
Longitudinal strips isolated from canine distributing muscular arteries were relaxed by noradrenaline [norepinephrine] and contracted by papaverine. This paradoxical relaxation and contraction may be due to a helical and circular arrangement of smooth muscle in the wall which is incompressible. Various vasoconstrictive agents, including noradrenaline, produced a circumferential contraction and longitudinal relaxation in muscular arteries. Vasodilator agents produced the opposite effect. The direction and magnitude of response of a helical strip to a vasoactive substance depended upon its sectioning angle from the transverse axis of the vessel.