Evaluation of tibolone effect on arterial resistance in postmenopausal women

Short-term tibolone does not interfere with endothelial function: a double-blinded, randomized, controlled trial

Objective To evaluate the effect of short-term hormone replacement therapy with tibolone 2.5 mg daily on endothelial function of healthy postmenopausal women, using flow-mediated dilation (FMD) of the brachial artery. Methods We performed a randomized, double-blinded, placebo-controlled study. A total of 100 healthy postmenopausal women were randomly allocated to receive tibolone (n = 50) or placebo (n = 50) for 28 days. Measurement of the FMD of the brachial artery was performed before and after the use of tibolone and placebo. Results A total of 31 women completed the study in the tibolone group, and 32 women completed the study in the control group. The results of the FMD measurements obtained from the women in the two groups before treatment were similar (0.018 and 0.091, for tibolone and placebo, p = 0.57). The values of the FMD in women who used tibolone and placebo, before and after the treatment, were similar in both groups. The numbers of women who presented an increase in the values of the FMD in both groups were also similar. Conclusion Our results demonstrate that the administration of 2.5 mg tibolone to healthy postmenopausal women for 28 days does not promote endothelial-dependent vasodilation, measured by FMD of the brachial artery.

Effects of tibolone on blood flow resistance and intima-media thickness of the carotid arteries: effect of time since menopause

OBJECTIVE

The aim of this prospective study was to evaluate the effects of tibolone on carotid atherosclerosis in healthy postmenopausal women.

METHODS

Twenty-five healthy postmenopausal women were included in the study. Patients received tibolone 2.5 mg daily for 6 months. Resistance indices of the common carotid artery (CCA), internal carotid artery (ICA), external carotid artery (ECA) and vertebral arteries, and intima-media thickness of the CCA were measured both at baseline and at the end of the study with ultrasonography.

RESULTS

No significant differences were observed in the resistance indices of the CCA, ICA, ECA and vertebral arteries, as well as intima-media thickness of CCA at 6 months in comparison with baseline. Tibolone significantly improved the intima-media thickness of the CCA of women who were less than 18 months since menopause.

CONCLUSION

Overall, these results demonstrate no significant effects of tibolone on either intima-media thickness or blood flow resistance in the carotid arteries in postmenopausal women. However, the results suggest that tibolone may have a positive effect on the vascular system if commenced within 18 months since menopause; this warrants further investigation.

Brachial artery responses in menopausal women using tibolone

OBJECTIVE

To determine the effect of tibolone treatment on brachial artery pulsatility index (PI), resistance index (RI), and flux-mediated dilation (FMD) in postmenopausal Mexican women.

METHOD

The FMD, PI, and RI of the right brachial artery were measured in 19 postmenopausal women before and after they received a hyperemic stimulus, first at baseline and then following a 6-month treatment with 2.5 mg of tibolone per day. Statistical analysis was performed using the t test.

RESULTS

The mean+/-SD age was 52.2+/-3.9 years; time since menopause was 24.6+/-16.7 months; and treatment duration was 5.7+/-2.0 months. Compared with prestimulus measurements, a significant poststimulus increase in arterial diameter and a significant decrease in PI were observed at baseline. Compared with prestimulus measurements, a significant poststimulus increase in arterial diameter and a significant decrease in both PI and RI were observed post-treatment.

CONCLUSION

Tibolone treatment had a favorable effect on brachial artery responses to hyperemic stimuli.

Tibolone activates nitric oxide synthesis in human endothelial cells

After the unexpected findings of the Women's Health Initiative trial, indicating that traditional cardiovascular risk markers fail to predict the effects of hormone replacement therapy, it is of interest to characterize how steroids act on vascular cells. This is particularly important for tissue-specific drugs such as tibolone, whose actions may differ from other preparations. Because nitric oxide (NO) is a key regulator of vascular tone and atherogenesis, we studied its regulation by tibolone and its metabolites on human endothelial cells. Tibolone and its estrogenic metabolites (3alpha- and 3beta-OH tibolone) activate NO synthesis by recruiting functional estrogen receptors, whereas the progestogenic/androgenic metabolite (Delta(4) isomer) has no effect. During prolonged exposures, tibolone and the estrogenic compounds enhance the expression of endothelial NO synthase (eNOS). In addition, tibolone is able to induce rapid activation of eNOS, leading to rapid increases in the release of NO. Relevant for its clinical effects, the sulfated metabolites of tibolone are also effective in activating eNOS. Different from estrogen, rapid activation of eNOS does not rely on recruitment of phosphatidylinositol-3 kinase but rather on MAPK-dependent cascades. These results help to understand the mechanisms of action of tibolone on the cardiovascular system and have relevant clinical implications.