Vasodilation

Vasodilation is the widening of blood vessels that occurs when the smooth muscle in their walls relaxes, lowering resistance and increasing blood flow.

Small arteries and arterioles are wrapped in a layer of muscle whose tone is set by the nervous system, hormones and local chemistry. Nitric oxide released by the vessel lining is the main dilating signal; adenosine, low oxygen, rising carbon dioxide, histamine and heat also relax the muscle. Dilation lowers blood pressure, warms the skin and delivers more blood to working muscle or inflamed tissue, and it is the reason for the flushing seen with fever, exercise and alcohol. Its opposite, vasoconstriction, narrows vessels and raises pressure.

Many blood-pressure medicines, nitroglycerin and sildenafil work by promoting vasodilation. The endocannabinoid system participates in vascular tone through CB1 and other receptors on vessel walls, and small short-term studies in healthy adults have reported acute blood-pressure changes after CBD that may involve vascular effects; these findings are preliminary and do not establish any use in high blood pressure.