Objectives: The aim of this study is to evaluate the relationship between plasma nitric oxide (NO) and β-endorphin levels in women using hormone replacement therapy (HRT) for 12 months. Material and Methods: Our study group was composed of 55 patients who were in at least their second postmenopausal year. Of the 55 patients, 25 were in the control group. All 30 women in the study group received 2 mg 17β-estradiol + 1 mg norethisterone acetate tablets daily for 12 months. Plasma NO and β-endorphin levels were measured both before and after the study period and possible relationships were analyzed. Results: There was a significant increase in both β-endorphin (p = 0.0001, 10.93 ± 2.25 vs. 14.85 ± 2.49) and NO (p = 0.0001, 19.79 ± 4.01 vs. 27.83 ± 10.27) levels measured after the study in the HRT group. A correlation was seen between the increments in β-endorphin and NO levels in the HRT group. Conclusion: Continuous combined HRT raises both plasma NO and β-endorphin levels and a close relationship was found between the two molecules after therapy. We postulate that the increment in these molecules may explain some of the beneficial effects of HRT on cognitive function and mood.

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