Comparative Study of Effects of Levarterenol and Methoxamine in Shock Associated with Acute Myocardial Ischemia in Dogs

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Abstract
Coronary arterial injections of levarterenol in dogs in shock from acute experimental myocardial ischemia (by selective coronary embolization with lycopodium spores) directly increased myocardial contraction and resulted in a lowering of both atrial and pulmonary arterial pressures while at the same time raising systemic arterial pressure. Appropriate intravenous administration of the same drug had similar effects and produced a greater rise in systemic arterial pressure. Methoxamine, when administered intravenously, elevated the lowered systemic arterial pressure, but produced a further elevation in the already high atrial and pulmonary arterial pressures. These experiments demonstrate that during acute myocardial ischemia with arterial hypotension, and even in the presence of elevated atrial and pulmonary pressures, a more favorable effect, i.e., increased systemic pressure at lower atrial and pulmonary pressures, is achieved by employing a pressor amine with a direct cardiac stimulating action which increases myocardial contraction in addition to a peripheral vasoconstricting effect. By selective coronary arterial injections, levarterenol has been shown to have a direct cardiac stimulating effect, and therefore satisfies the above requirement, whereas methoxamine does not, since it fails to stimulate myocardial contraction, or actually depresses it, when given into the same site.