Systemic study of the hemodynamic effects of sublingual nitroglycerin in unanesthetized dogs

The cardiovascular effects of nitroglycerin, given sublingually and intravenously in a clinical dose range, were studied in unanesthetized and unrestrained normal dogs. The parameters examined included coronary blood flow, coronary conductance arterial diameter, internal diameter of the left ventricle, blood flow in the aorta and vena cava, diameters of the aorta, carotid, mesenteric, iliac, internal thoracic and pulmonary arteries and vena cava, pressures in the left ventricle, abdominal aorta and pulmonary arteries, organ thickness of the spleen, liver and sartorius muscle, and rate of rise in arterial pressure pulses. It was suggested that nitroglycerin does not dilate the veins in the splanchnic area and hind limb, but efficiently dilates conductance arteries. It was concluded that the therapeutically important effects of nitroglycerin involve the dilatation of conductance arteries, including both coronary and general systemic arteries. The effect of the former would be directly on stenotic lesions in the epicardial large coronary artery, improving blood flow to the ischemic part of the myocardium, whereas the latter might be beneficial for reducing cardiac work and lowering systolic pressure by increasing the Windkessel volume. Therefore, the heart regains its ventricular function and pumps stagnant blood from heart, lungs and veins to the arterial side, resulting in a reduction of the elevated preload to normal levels in anginal patients.