Background Prostaglandin E sub 1 is a potent vasodilator with anti-inflammatory and antiplatelet effects. We tested the hypothesis that prostaglandin E1attenuates or prevents platelet aggregation-associated cyclic flow variations (CFVs) in severely stenosed and endothelium-injured coronary arteries.Methods and Results We induced CFVs in 21 dogs by placing an external constrictor around the left anterior descending coronary artery at the site where the endothelium had been mechanically injured. The blood flow velocity in the artery was monitored by a pulsed Doppler flow probe. Sixty minutes after CFVs were established, liposome-bound prostaglandin E1, a stable formulation, was administered intravenously to 12 dogs at incremental doses of 0.25, 0.5, 1, and 2 micrograms/kg body wt; it abolished CFVs in 8 of the 12 dogs (67%). After CFVs were eliminated, epinephrine was infused intravenously, and at a dose of 6.6+-1.6 micrograms/min, it restored CFVs in 7 of 7 dogs. Control dogs (n=9) were treated with free prostaglandin E1, which did not abolish CFVs in any dog.Conclusions Liposome-bound but not free prostaglandin E1effectively diminishes CFVs in severely stenosed and endothelium-injured canine coronary arteries. (Circulation. 1994; 89:1786-1791.)