Steroid-induced thrombogenesis in rats

Oral contraceptives have been associated with the development of thrombotic episodes in humans in various epidemiologic studies. Studies in laboratory animals have failed to provide evidence that sex hormones cause increased thromboses. Uzunova, Ramey, and Ramwell published data suggesting that male animals had more severe clotting problems following cannulation of the aorta than females, and that such problems were exacerbated by testosterone and ameliorated by estradiol. We attempted to confirm the testosterone effect and to extend the observations to such androgenic progestogens as norgestrel and norethindrone, and to ethinylestradiol, the estrogenic component of many oral contraceptives. None of these steroids had any measurable effect on cannula-induced thrombogenesis in rats, nor were "prothrombin times" affected. We conclude that another potential model for thrombogenesis in laboratory animals has failed to provide evidence for the putative effect of oral contraceptives in women.