one of a group of pharmacological agents that cause the smooth muscles of blood vessels to relax, which results in the widening of vascular lumens. Several groups of vasodilators are distinguished according to their mechanism of action and chemical structure.
Myotropic agents directly affect the muscular elements of the vascular wall, altering the metabolic processes and decreasing the tone of the elements. They include such purine derivatives as caffeine and theophylline, such isoquinoline derivatives as papaverine, drotaverine, salsoline, and such chromone derivatives as kellin.
Neurotropic agents exert a vasodilative effect through their influence on the neural regulation of vascular tone. They may have peripheral or central action. Those with peripheral action include adrenolytic agents, which block the adrenergic receptors of blood vessles (for example, phentolamine), and sympatholytics, which block the transmission of excitation from the endings of the sympathetic nerves that innervate blood vessels (for example, oktadin and ornid).
Other vasodilators include cholinomimetic and ganglion-blocking agents. The former, which include acetylcholine and carba-chol, facilitate the transmission of excitation from parasympathetic nerves to effector organs, including blood vessels. The latter, which include Tetamon (sympatektoman), Hexonium (esametina), and pentamin, impede the transmission of excitation in the sympathetic ganglia, resulting in a decrease in vascular tone. Derivatives of hydrazinophtalazine (for example, Apressin [Ap-resoline]), and of phenothiazine (for example, aminazine), affect the central regulation of vascular tone.
Some drugs have a mixed mechanism of action and may be centrally neurotropic and peripherally myotropic. These drugs include nitrites and nitrates (amyl nitrite, nitroglycerin, nitranol) and reserpine, which is an alkaloid isolated from the tropical plant rauwolfia. Reserpine weakens the central and peripheral adrenergic innervation of blood vessels, causing the vascular lumens to dilate and arterial pressure to decrease.
Vasodilators are used mainly in the treatment of ischemic heart disease, hypertension, and cerebrovascular disorders. They are also used in surgery to reduce bleeding (by lowering arterial pressure). Many vasodilators also have other pharmacological effects.
V. V. ZAKUSOV