Effects of tibolone on plasma levels of nitric oxide in postmenopausal women.

Objective: To determine the effects of tibolone on nitric oxide (NO) plasma levels in postmenopausal women.

Design: Randomized, double-blind, placebo-controlled, cross-over trial.

Setting: Healthy volunteers in an academic research environment.

Patient(s): Eighteen healthy women who have been in postmenopause for 1-4 years.

Intervention(s): Women received either tibolone 2.5 mg/day (group A) or placebo (group B) for 1 month; then the treatment was inverted for the second month.

Main Outcome Measure(s): Plasma concentration of NO stable oxidation products and blood pressure were evaluated at baseline, month 1, and month 2.

Result(s): Baseline concentration of NO metabolites were similar in both groups. At month 1, mean concentration of NO metabolites increased significantly in group A alone. At the end of month 2, NO metabolite levels in group A returned to baseline, whereas in group B they increased significantly.

Conclusion(s): Tibolone induced a sustained increase in plasma levels of NO in postmenopausal women, suggesting that tibolone may exert a direct cardiovascular protective effect in postmenopausal women.