Estrogens and contraceptives as thrombotic drugs: assays of thrombus formation platelet aggregation and adhesiveness.

The estrogens ethinyl estradiol and mestranol and oral contraceptives containing these estrogens enhanced thrombus formation in a rabbit extracorporeal carotid-jugular shunt. 3 mcg/kg/day orally for 3 days increased thrombus weight by 150% (p less than .01). The contraceptives Demulen Enovid E and Norinyl 2 given at levels containing 3 mcg/kg of the estrogen also increased thrombus weights but to a significantly lesser extent than did estrogen itself. The progestins in the contraceptives had an apparent protective effect but had no thrombotic or antithrombotic activity when given alone. Bleeding time was reduced in rabbits receiving the estrogens and contraceptives. Base-line blood platelet counts were elevated after estrogen treatment and platelet consumption across the shunt was increased by the estrogens. The thrombocytosis was less marked in animals receiving the combination contraceptives. The results of initial assays of the effect of estrogen treatment on platelet aggregation (ADP and collagen) and adhesiveness were variable. It is not possible to say at this time whether the observed increase in thrombus formation occurs in parallel with changes in platelet behavior.(FULL TEXT)