Studies on antiplatelet effect of OP-41483, a prostaglandin I2 analog, in experimental animals. 1. Effect on platelet function and thrombosis.

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Abstract
Antiplatelet and antithrombotic effects of OP-41483, a PGI2 analog, were studied in experimental animals, and the following results were obtained: 1) With 10 min-intravenous infusion to guinea pigs, OP-41483 inhibited platelet adhesiveness and platelet aggregation at 300-1000 ng/kg/min and 1000 ng/kg/min and 1000 ng/kg/min. respectively. In these effects, OP-41483 was 1-3 times more potent than carbacyclin and 3 times less potent than PGI2. 2) With oral administration to guinea pigs. OP-41483 given as its .alpha.-cyclodextrin clathrate (OP-41483 .alpha.-CD) inhibited platelet adhesiveness at doses higher than 1.0 mg/kg (expressed in terms of OP-41483). Whereas PGI2 and carbacyclin did not at 10 mg/kg. OP-41483 .alpha.-CD also inhibited platelet aggregation after a single dose of 3 mg/kg and repeated doses of 3 mg/kg/days. 3) In the electrically induced thrombosis model of guinea pig mesenteric artery, OP-41483 (300-1000 ng/kg/min. i.v.-infusion) and OP-41483 .alpha.-CD (1.0-3.0 mg/kg, p.o.) inhibited thrombus formation, but heparin (1.0-10 U/kg/min, i.v.-infusion) did not. 4) In the rabbit extracorporeal circulation thrombosis model, OP-41483 (100 and 300 ng/kg/min, i.v.-infusion) inhibited thrombus formation in the extracorporeal shunt and prevented the decrease in platelet count. hematocrit and fibrinogen level in circulating blood. Heparin (1.0-3.0 U/kg/min, i.v.-infusion) also inhibited the thrombus formation and the decrease in fibrinogen level, but did not inhibit the decrease in hematocrit and platelet count.