Recruitment of inotropic reserve in “stunned” myocardium by the cardiotonic agent AR-L 57

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Abstract
Contractile dysfunction of reversibly injured, reperfused myocardium can be enhanced by inotropic interventions. A decrease in the Ca-sensitivity of contractile proteins with slow recovery during reperfusion has been suggested as a potential mechanism underlying this postischemic dysfunction. We therefore tested the effects of the cardiotonic agent AR-L 57 (1 mg/kg i.v.) in six anesthetized, vagotomized dogs during constant atrial pacing at 192±6 beats/min. Before ischemia, AR-L 57 increased left ventricular pressure from 131±22 to 138±21 mm Hg and maximum dP/dt from 3,022±1,427 to 4,337±2,608 mm Hg/s. Mean systolic thickening velocity of the posterior myocardium was increased from 8.9±1.1 to 11.7±1.1 mm/s. After release of a 15 min LCX-occlusion which caused complete regional akinesia, baseline function in the posterior myocardium was severely depressed and only gradually returned towards control values over 8 h of reperfusion. AR-L 57 increased systolic thickening velocity at 10 min, 4 and 8 h reperfusion to a similar extent as before ischemia. With reference to a purported Ca-sensitizing mechanism underlying the positive inotropic action of AR-L 57, our data suggest no change in the Ca-sensitivity of reperfused myocardium.

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