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Estrogen-Containing Oral Contraceptive Agents

1976; American Medical Association; Volume: 236; Issue: 19 Linguagem: Inglês

10.1001/jama.1976.03270200017021

1538-3598

Stanford Wessler,

Enzyme Production and Characterization

The mechanism whereby estrogen-containing contraceptives facilitate thrombosis is obscure, and published data concerning their effect on anti-thrombin III are conflicting. Plasma samples were examined for the quantity of antithrombin III and activated factor X (Xa) inhibitory activity among 57 women receiving oral contraceptives and 48 controls. The quantity of anti-thrombin III in both groups was normal. In contrast, Xa inhibitory activity was significantly reduced ( P <.001) among patients taking oral contraceptives, compared to controls. Heparin sodium added to plasma from patients taking contraceptives raised Xa inhibitory activity toward or above normal without changing the quantity of antithrombin III. The effect of estrogen is not to decrease the quantity of plasma antithrombin III, but rather to diminish plasma Xa inhibitory activity, an effect that can be abolished by heparin. ( JAMA 236:2179-2182, 1976)