Effect of synthetic estrogen on platelet aggregation and vascular release of PGI2-like material in the rabbit.

Treatment of adult female New Zealand white rabbits with ethinyl estradiol, the synthetic estrogen used in many oral contraceptives, results in a significant increase in in vivo aggregation. This alteration in platelet behavior is accompanied by diminished vascular release of antiaggregatory PGI2 (prostacyclin)-like material. Addition of a progestin prevents the change in platelet aggregation seen with the estrogen alone. Diminished vascular PGI2 release may be an important factor in the pathogenesis of thrombotic occurrences experienced by some oral contraceptive users. In vivo platelet aggregation may be of value in identifying individuals at risk of developing thrombotic disturbances while taking oral contraceptives.