Effects of oral contraceptives, or lanosterol, on ADP-induced aggregation and binding of 125I-fibrinogen to rat platelets

Oxidative status and oral contraceptive. Its relevance to platelet abnormalities and cardiovascular risk

Oral contraceptive (OC) use is a risk for thrombogenic events. This paper reviews effects of OC on oxidative status, coagulation, and platelet activity. Complicating effects of cardiovascular risk factors such as smoking, diabetes, hyperpidemia, and hypertension, are discussed. From these data we conclude that: 1. OC use modifies slightly but significantly the oxidative status in women and in animals by decreasing in plasma and blood cells the antioxidant defenses (vitamins and enzymes). 2. The changes in the oxidative status are related to an increase in plasma lipid peroxides apparently responsible for the hyperaggregability and possibly the imbalance in clotting factors associated with the OC-induced prethrombotic state. 3. These effects of OC appear to be increased by a high intake of polyunsaturated fat and counteracted by supplements of vitamin E. 4. The risk factors acting synergistically with OC, have all been shown to increase platelet reactivity. In addition, smoking, diabetes, and, to some extent, dyslipidemia are associated with an increased level of lipid peroxides and concomitant changes in the antioxidant defenses that can be additive to those induced by OC. Thus, free radicals and lipid peroxidation could be the underlying mechanism in the predisposition to thrombosis induced by most risk factors in OC users. 5. Results of epidemiologic and experimental studies in this field will be concordant only when diet and natural antioxidants will be systematically taken into consideration.

Oral contraceptive steroid induced platelet coagulant hyperactivity: dissociation of in vivo and in vitro effects

The use of oral contraceptives (OC) has been associated with an increased risk of thromboembolic events in a subset of women. Factors predisposing to this problem are still not clearly defined although an increased platelet coagulant activity (CA) has been reported. This study was designed to evaluate the CA of platelets from asymptomatic current OC users compared with control subjects. The asymptomatic OC users were found to have evidence of hypercoagulability in the form of increased availability of platelet CA. These findings were present in both collagen stimulated and unstimulated platelets. In order to understand the mechanism we examined the in vitro effects of estradiol and/or progesterone on platelets. Platelets from normal males were incubated for one hour with estrogen and/or progesterone. There was no significant difference in CA of hormone treated platelets compared with control platelets from the same donor. CA was analyzed in platelets exposed to epinephrine, adenosine diphosphate, and collagen in the platelet aggregometer. Although a dose dependent effect was observed on CA of platelets exposed to the range of aggregating agents, the results show no significant difference between CA of the hormone treated and control platelets (p greater than 0.05). Likewise, platelet aggregation and release of nucleotide were not different between hormone treated and control platelets. Thus a direct effect of the hormones on platelets is an unlikely mechanism causing the increased CA seen in OC users.

Prostanoid mediated effects of centchroman, a non-steroidal oral contraceptive

The effect of centchroman, a non-steroidal oral contraceptive, has been studied on platelet aggregation and on the products of arachidonate metabolism. Centchroman inhibited platelet aggregation in vitro and ex vivo after acute as well as chronic treatment for one year in laboratory animals. It did not affect aggregation of platelets in women taking centchroman for one year. It is an inhibitor of platelet cyclooxygenase as indicated by the inhibition of malonaldehyde and thromboxane B2 but has no effect on vascular cyclooxygenase activity ex vivo or at low concentration in vitro. Thus, centchroman is a safe antifertility agent without risk of thrombotic episodes associated with hormonal oral contraceptives.