Effects of combined oral hormone replacement therapy on tissue factor pathway inhibitor and factor VII

Oral combined hormone replacement therapy (HRT) with oestradiol and norethi sterone increases plasma levels of prothrombin fragment 1 + 2 (F1 + 2), ind icating an increase in thrombin generation, but the mechanisms underlying t his increase are uncertain. The aim of this randomized, placebo-controlled study was to determine whether an increase in factor VII, a factor that com bines with tissue factor to activate the extrinsic pathway, or a decrease i n tissue factor pathway inhibitor (TFPI), an inhibitor of extrinsic pathway activation, may contribute to increases in thrombin generation occurring w ith HRT. Healthy postmenopausal women aged 50-75 years received placebo (n = 19) or oral combined H RT (n = 18) and had blood collected for measuremen t of factor VII coagulation activity (VIIc), activated factor VII (VIIa) an d TFPI at baseline and at 6 weeks. Baseline characteristics were similar in the two groups, including age, body mass index and cholesterol levels. As reported previously, HRT increased the F1 + 2 concentration by 20%. Placebo had no effect on VIIc, VIIa or TFPI, but 6 weeks of combined HRT decreased VIIc [from 1.1 +/- 0.06 (mean +/- S.E.M.) to 1.03 +/- 0.06 i.u./ml; P < 0. 03], VIIa [from 43.9; 10.8-198.3 (median; range) to 35.0; 6.3-66.8 m-units/ ml; P < 0.03] and TFPI [from 81.3 +/- 6.5 to 60.4 +/- 5.5 ng/ml; P < 0.0001 ]. The decrease in TPFI with HRT was not correlated with the elevation in F 1 + 2 levels. In conclusion, the increase in thrombin generation seen with HRT is not due to an effect on factor VII; in addition, while a contributio n from the decrease in TFPI is possible, increased thrombin generation is n ot directly related to the decrease in TFPI.