Male Wistar rats were treated with MY-5445 (50 mkg/paw) as a single dose.

Human citrated PRP containing 5 x 10^6 platelets/mkl was prepared from blood obtained from healthy volunteers. The effect of MY-5445 on platelet aggregation was studied by the turbidimetric method, with an aggregation meter (RAM41; Rikadenki Kogyo Co., Ltd., Japan). MY-5445 (5 mkl) was added to 0.25 ml of PRP and incubated at 37’C with stirring for 2 mm before the addition of aggregating agents (25 zl of collagen, ADP or arachidonic acid). Final concentrations ofeach aggregating agents were 3 mkM ADP, 3 mkg/ml collagen and 100 mkg/ml arachidonic acid. The extent of aggregation was expressed by the maximum change of light transmission for PRP and platelet-poor plasma as a value of 100%. The percent inhibition of aggregation by the test compounds was calculated by dividing the percent aggreıtion in the presence of the test compound by that observed in the control run, and multiplying by 100.