Effects of hormone replacement therapy on hemostatic cardiovascular risk factors

OBJECTIVES: From observational studies, there is evidence that hormone replacement therapy in postmenopausal women causes a decrease in cardiovascular events. It remains unknown, however, precisely by which mechanisms this reduction is achieved. The primary aim of this work was to study the effects of hormone replacement therapy on established hemostatic risk factors during 1-year treatment of healthy postmenopausal women. The secondary aim was to investigate whether there was any significant difference in these risk factors between hormone replacement therapy administered as a cyclic estrogen/sequential progestogen or continuous estrogen/sequential progestogen regimen. STUDY DESIGN: Sixty postmenopausal women were randomized to treatment with estradiol valerate 2 mg/day either continuously or cyclic (days 1 to 21, placebo on days 21 to 28). Both groups received cyproterone acetate 1 mg/day on days 12 to 21. Blood samples were collected before treatment and on cycle days 17 to 22 in cycles 3, 6, and 12. Thirty women with basic characteristics identical to the women included in the treatment group were included as a reference group. Blood samples were collected after 0, 6, and 12 months of observation. RESULTS: Hormone replacement therapy during 1 year caused a marginal but significant increase in plasma concentration of factor Vile after 12 months of treatment (P < .05), a significant decrease in fibrinogen, and a significant decrease in the protein concentrations of tissue-type plasminogen activator, plasminogen activator inhibitor-1, and lipoprotein(a) after 3, 6, and 12 months of treatment (P < .05). Possible differences in the integrated response between the reference group and the hormone replacement therapy group were evaluated by comparison of the area under the curve as estimated in each individual on the basis of each analyte in the sampling periods. The area under the curve of fibrinogen was significantly lower in the hormone replacement therapy group than in the reference group (P < .03), whereas other variables did not deviate significantly between the groups. The areas under the curve did not deviate significantly between the group that received cyclic estrogen/sequential progestogen and the group that received continuous estrogen/sequential progestogen. CONCLUSIONS: One-year treatment with hormone replacement therapy influenced favorably a number of prognostic cardiovascular risk factors in healthy women. The most important effect was the lowering of fibrinogen. Furthermore, in this study the effect of hormone replacement therapy on hemostasis did not deviate between a cyclic estrogen/sequential progestogen regimen and a continuous estrogen/sequential progestogen regimen.