The organic nitrates, including nitroglycerin, isosorbide dinitrate and isosorbide mononitrate, act as prodrugs for nitric oxide (NO) which is a potent vasodilator gas. Nitric oxide activates guanylyl-cyclase in vascular endothelial cells, which increases intracellular cyclic GMP and thereby reduces intracellular calcium concentrates and dephosphorylates myosin light chains causing relaxation of smooth muscle cells.