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The physiological importance of proteins C and S as natural anticoagulants is demonstrated by the increased risk of thromboembolic disease among subjects with hereditary deficiency of both proteins. In the present study the effects were evaluated of low-dose oestrogen oral contraceptives (OC) on the plasma levels of immunological protein S, as free (PS-f), and in reversible complex with C4b-binding protein as well as functional protein C (PC) in a homogeneous group of 20 young healthy women. The participants were randomly given either gestodene (75 micrograms) or desogestrel (150 micrograms) in combination with ethinyl oestradiol (30 micrograms). Blood samples were taken prior to the initiation of the treatment and at the end of the sixth 21-day treatment cycle. The mean concentration of both free and bound PS fell significantly, the decrease still being within the reference range. Conversely, the plasma values for PC rose to a statistically significant extent. There were no significant differences between the two OCs. Hypothetically, the changes in PS-f (active fraction) might be conducive to a procoagulant state, which the increased PC may compensate. The reverse effect of two OCs on the activity of the protein C-protein S anticoagulant system might suggest a different regulation of their synthesis.

It is generally assumed that the oral contraceptives cause the carrier proteins to change. Notoriously this effect is used to evaluate indirectly their estrogenicity/gestagenicity ratio. In order to assess the residual intrinsic androgenic activity of two new 19-nor-derivative components, Desogestrel (DG) 150 micrograms and Gestodene (GD) 75 micrograms, both in association with Ethinylestradiol (EE) 30 micrograms, Sex Hormone Binding Globulin, Thyroxine Binding Globulin, Ceruloplasmin and Free Androgen Index (FAI), were studied in 40 young normally cycling healthy volunteers, matched for body mass index and age. The participants were randomly assigned to either EE-DG or EE-GD treatment. A marked significant increase in all the carrier proteins was found. Conversely, the values for FAI decreased significantly. The changes in the two groups were substantially of the same magnitude. These results are an indirect confirmation of the well-known negligible receptor binding affinity of the two progestogen in vitro, also supporting for these compounds the lack of relevant androgenic effects.