The vasodilator substances produce local dilation of blood vessels and relaxation of precapillary sphincters. The result is the increase in blood flow to the tissue, organ, or region which increases the oxygen level.
Vasodilation. Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins (called venodilators), large arteries, and smaller arterioles. ... Endogenous substances and drugs that cause vasodilation are termed vasodilators.