Contraction of Vascular Smooth Muscle in Response to Plasma

Addition of plasma to the physiologic salt solution in which helical strips of vascular smooth muscle were suspended caused the muscle to contract. The plasma was obtained from dog arterial blood which, extracorporeally, had been in contact only with siliconized polyethylene in the cold. The strips were from large and small vessels from several sites in rabbit and dog. The contractions were reproducible and dose dependent. Threshold concentrations for contraction ranged from 2% to 30% depending on the source of the smooth muscle. In concentrations too low to produce contraction, plasma potentiated tension developed in response to stimulation by epinephrine, angiotensin, and KC1. The response of the strips to plasma was compared with their response to the several known vasoactive agents of plasma: epinephrine, norepinephrine, serotonin, angiotensin, vasopressin, bradykinin and histamine. Important differences were found. It is possible that in normal plasma there is an as yet undefined vasoactive component which in situ may play a role in the maintenance of vascular tone.