INFLUENCE OF NORETHISTERONE ACETATE AND ESTRADIOL ON THE SEROTONIN METABOLISM OF POSTMENOPAUSAL WOMEN

Previous studies have shown that estradiol increases urinary excretion of the main stable metabolite of serotonin, 5-hydroxyindole acetic ac id (5-HIAA), reflecting an increase in serotonin production. In the pr esent study, the effect of the progestin norethisterone acetate (NETA) on serotonin metabolism was investigated, both alone and in addition to estradiol replacement in 20 postmenopausal women. Urinary excretion of 5-HIAA was measured after treatment with NETA orally for 8 days, e stradiol valerate orally for 9 days and a combination of both hormones for 12 days. 5-HIAA values, expressed as percentages of the pretreatm ent values, were significantly increased only after the estrogen treat ment phase. NETA alone did not significantly alter the serotonin metab olite excretion; in combination with estradiol, the estradiol effect o n serotonin metabolism was abolished. This indicates that adding noret histerone acetate to estradiol replacement therapy may have a negative impact on the effect of estradiol on serotonin metabolism.