Sex differences in stroke: the contribution of coagulation.
The effects of endogenous and exogenous, synthetic ovarian hormones on thrombus formation have been examined using an in vivo model in the rat. Thrombus formation in female rats was greatest during the di-oestrus stage of the oestrous cycle. Thrombus formation in both male and female rats was reduced following 6 weeks treatment with the oestrogen, ethynyl oestradiol whilst in females the progestogen, norethindrone acetate had no effect. These findings are in contrast to the increased risk of thromboembolic disorders reported in women taking oral contraceptives. The inhibitory effect of ethynyl oestradiol was not due to changes in blood flow but was dependent on the heparin concentration, being greatest at the highest heparin concentration used. Thrombus formation was greater in male rats than in females, a sex difference which is consistent with the higher incidence of cardiovascular disease in men than in women.