The effect of monensin, a Na+-selective carboxylic ionophore, on coronary circulation

Abstract

Carboxylic ionophores are antibiotics that selectively complex with cations and facilitate their transport across biological membranes. Monensin is a monovalent ionophore that has been reported to exhibit a high degree of in vitro selectivity to transport Na+ ions. In anesthetized dogs, intravenous injections of 5-25 micrograms/kg of monensin produce a selective coronary vasodilator action. A maximal increase in coronary blood flow (CBF) with little or no effect on other cardiovascular parameters was produced. In the 50-200-micrograms/kg dose range, additional positive inotropic and systemic vasopressor effects were elicited. In dogs with normal coronary arteries, 25 micrograms/kg i.v. of monensin increased both subendocardial (ENDO) and subepicardial (EPI) blood flows, such that the ENDO/EPI ratio was changed from 1.10 +/- 0.03 before to 0.75 +/- 0.05 after monensin. The large dose (75 micrograms/kg i.v.) of monensin produced a maximum increase in ENDO flow but the EPI flow was less than that with the small dose; the ENDO/EPI ratio was increased to 1.19 +/- .14. In dogs with 80%-90% occlusion of the left anterior descending (LAD) coronary artery, both doses of monensin increased blood flow to normal and "border" zones but not the central ischemic zone. There was no evidence of "coronary steal" after monensin. This ionophore may be useful in increasing blood pressure and cardiac output after acute myocardial infarction.