Prostaglandin E1 increases myocardial contractility in the conscious dog

The systemic and inotropic properties of prostaglandin E1 (PGE1) were investigated in 20 unanesthetized dogs. Pairs of ultrasonic dimension gauges and a micromanometer were implanted in the subendocardium and the apex of the left ventricle (LV), respectively. Seven to ten days later, increasing doses of PGE1 were infused into the left atrium. To appreciate the inotropic effects of the agent, the heart rate was maintained constant at 150 beats/min in a subgroup of dogs while preload was modified by bleeding or saline infusion over matched ranges of end-diastolic segmental length (EDL) during placebo and PGE1 infusions (0.25 microgram . kg-1 . min-1). LV function curves (delta L: systolic segmental shortening versus EDL) were plotted. Increasing doses of PGE1 above 0.031 microgram . kg-1 . min-1 brought a progressive decrease of left ventricular end-diastolic pressure, EDL, delta L, and peak left ventricular systolic pressure. The heart rate increased significantly at dosages from 0.063 to 0.125 microgram . kg-1 . min-1, and peak positive dP/dt after an initial increase fell at the dose of 0.5 microgram . kg-1 . min-1. The LV function curves invariably showed a shift to the left when PGE1 was administered; as the basal EDL was restored during PGE1 infusion, delta L reached a 33% increase (p less than 0.001). Thus, in addition to its potent vasodilating properties that are more prominent on preload than afterload, PGE1 increases myocardial contractility in the conscious dog.