The following are endothelium-independent vasodilators except:
A. NitroglycerinAcetylcholine (ACh). ACh, acting through muscarinic receptors, exerts its effect on the endothelium by promoting the conversion of L-arginine to NO. This in turn produces smooth muscle cell relaxation and consequent vasodilation. ACh is therefore an endothelium-dependent vasodilator. In patients with endothelial dysfunction, this effect is lost, and the direct action of ACh on smooth muscle cells producing vasoconstriction is more pronounced. The other agents listed are all endothelium-independent vasodilators.