Vasodilating Action of Substance P in the Human Forearm

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Abstract
The vasodilator activity of substance P in the human forearm has been studied using venous occlusion plethysmography. The effects have been compared to those of bradykinin. The compounds were given as single injections or infusions into the brachial artery or the antecubital vein. I.a. administration caused a significant increase in skin and muscle blood flow in doses of more than 0.5 units of substance P per min. The oxygen saturation of blood from both deep and superficial veins of the forearm increased. These effects were not influenced bvatropine, antihistaminics or guanethidine. Stellate ganglion block increased the resting blood flow as well as the vasodilating action of both polypeptides. I.v. infusion c f substance P and bradykinin also caused an increase in forearm blood flow coincident with tachycardia and flushing of the face and the neck. During substance P infusion the increase in forearm blood flow and flushing appeared simultaneously, while bradykinin caused an increase in the forearm blood flow only in doses which were almost intolerable for the subjects due to severe pulsations and flushing of the skin of the head and the neck. The ratios between equieffective doses of substance P and bradykinin on the forearm blood flow were about 1:10 at i.a. infusion and about 1:200 at i.v. infusion.

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