Changes in the plasma levels of proteins C and S in young women on low-dose oestrogen oral contraceptives.

ABSTRACT

PIP: The influence of low-dose oral contraceptives (OCs) on plasma levels of proteins C and S was investigated i 20 healthy women. These proteins, along with antithrombin III, are the most significant inhibitors of coagulation. Blood samples were collected after 6 months of treatment with an OC containing 30 mcg of ethinyl estradiol and either 150 mcg of desogestrel or 75 mcg of gestodene. A significant increase in functional protein C concentrations (from 55.70 + or - 9.84 to 117.48 + or - 21.29 in the desogestrel group and 68.80 + or - 19.11 to 135.60 + or - 28.66 in the gestodene group) was recorded between baseline and the 6-month measurement. There was a corresponding decrease in plasma concentrations of free protein S (from 98.48 + or - 9.64 to 73.96 + or - 12.07 in the desogestrel group and 104.79 + or - 31.52 to 83.14 + or - 18.28 in the gestodene group). Although these OC-induced changes were statistically significant, all values remained within the normal range. The differences between the 2 OC formulations were not significant. It is hypothesized that the changes in the active fraction of protein S recorded in OC users produce a procoagulant state and increases in protein C reflect an effort to compensate for this change. The findings that OC use increases protein C and decreases protein S values suggests that the two proteins differ in the regulation of their synthesis.