Resistance of pelvic arteries and plasma lipids in postmenopausal women:: Comparative study of tibolone and continuous combined estradiol and norethindrone acetate replacement therapy

OBJECTIVE: We sought to compare vascular resistance and plasma lipids in postmenopausal women assigned to tibolone (a synthetic estrogen replacement steroid) therapy or continuous combined hormone replacement therapy. STUDY DESIGN: Pulsatility and resistance indexes in pelvic arteries (color Doppler transvaginal ultrasonography) and lipids were monitored in this double-blind 1-year trial of 100 women randomized to either 2.5 mg tibolone or 2 mg 17 beta-estradiol plus 1 mg norethindrone acetate daily. RESULTS: Both indexes of the arcuate arteries (uterine arteries) were significantly reduced beyond 3 and 6 months (12 months) from baseline, respectively, by the combined regimen compared with tibolone alone. Tibolone increased the resistance index of arcuate arteries but did not affect uterine arteries. There was no effect of either regimen on the internal iliac arteries. The medians of the percentage changes from baseline of high-density lipoprotein cholesterol (triglycerides) were significant between groups after 1 year, as follows: -17% (-16%) in the tibolone group and -4% (+15%) in the combined group, respectively. Both regimens similarly reduced total and low-density lipoprotein cholesterol and lipoprotein Lp(a). CONCLUSION: Hormone replacement therapy may induce different or opposite changes of both vascular resistance and lipids. It is unknown whether these findings may modify cardiovascular risk.