Abstract
Although the question whether oral contraceptives are casually involved in thromboembolic disorders remains a very contested issue, a growing number of studies show that a state of hypercoagulability does exist in users of oral contraceptives, and there seems to be general agreement that factors II, VII, X and fibrinogen are increased and antithrombin III (AT III) decreased. Reduction in the level of this inhibitor in this case has been repeatedly confirmed both by coagulant and immunological methods. Many familial cases of thromboembolic disorders due to AT III deficiency have been reported and one of authers showed hyper sensitivity of platelet to thrombin. The recent observation by Fukutake and Nagasawa et al. showed the reduction of AT III measured by coagulant and immunological methods after the addition of estrogen to the plasma in vitro.
Our test system was consisted with platelet, AT III and thrombin. It was set up as next; Platelet was suspended in Ca-free Tyrode buffer and platelet aggregation was induced by vovine thrombin (0.01 NIH unit) containing lowest activity which can produce 100% aggregation. And this 100% aggregability of platelet was supressed to 0-5% by the addition of AT III with lowest concentration (0.06u) 2min prior to thrombin. Platelet aggregation was measured as optical transmission based on Born's method, and purified in highest degree materials were used. This aggregation curve as a control for the next study almost nothing in aggregability.
When 17β estradiol desolved in Tyrode buffer containg 0.05% ethanol was added to platelet suspension previously, platelet aggregation was increased up to 100% in a dose dependent manner. This effect was observed by the addition of estrogen 1.25×10-7-1.25×10-10M in final concentration.
The same effect was also observed by the addition of estradiol, progesteron, testosterone, cortisone and cholesterol which are all clasified as a steroid group. There seemed to be no difference in the effect between these steroides. Not only estrogen but also all other samples could not produce any platelet aggregation in another system consisted with only platelet nor platelet and thrombin.
Our in vitro test system is similar to the mechanism of hemostasis on the blood coagulation in the body. The results interprete the mechanism of thromboembolic disorders due to the administration of oral contraceptives through the inhibition of neutralizing activity in AT-III against thrombin, and this phenomenon produce predominance of thrombin resulting platelet aggregation.
