The effect of temperature on vascular smooth muscle: cooling-induced vasodilation in deep arteries and veins.

Blood vessels in the cardiovascular system include arteries and veins, which are responsible for moving blood to and from tissues around the body. Our previous studies showed that cooling induces relaxation of arteries. The aim of this study is to investigate the effect of cooling on both arteries and veins pairs. Isometric tension was recorded in rat artery ring preparations (aorta, carotid, pulmonary arteries) and their vein pairs (vena cava, jugular, pulmonary veins) in organ baths during stepwise cooling from 37 to 4 °C. Cooling responses were tested before and after the addition of various standard agents. The possibility of the presence of a cooling-relaxed substance and the influence of endothelium were also examined. Cooling-induced relaxation of both arteries and veins and the degree of relaxation were inversely proportional to the temperature. The cooling response was highest in arteries than their respective paired veins. The relaxation response was not endothelium dependent or affected with neurogenic mechanism (autonomic blockers or tetrodotoxin). Additionally, it was not changed by alterations of extra- or intra-cellular calcium transfer, and no relaxant substance was released from vascular smooth muscles during cooling. The study showed that cooling induces relaxation of both arteries and veins. Our results suggested that the effect of cooling could be through a thermal receptor in the vascular smooth muscle. Therefore, cold temperature can act as an agonist and increase in cooling temperature behaves as increase in concentration of the agonist. This study contributes to a better understanding of the mechanisms behind cooling-induced relaxation of blood vessels, which may have implications for the treatment of cardiovascular diseases.