Modulation of plasma endothelin levels by the menstrual cycle

Blood pressure varies during the menstrual cycle, but the reason for this i s unclear. Administration of (synthetic) sex hormones can influence the lev el of vasoactive substances such as endothelin (ET). However, it is not kno wn whether short-term variations in sex hormone levels in physiological sit uations affect ET levels. We assessed the effects of the menstrual cycle on plasma ET-1 in 8 healthy premenopausal women not using oral contraceptives (OCs) and 8 premenopausal women using OCs. ET-1 levels were measured in al l subjects on days 1 to 3 (menstrual phase), 9 to 12 (follicular phase), an d 20 to 23 (luteal phase) of the menstrual cycle. ET-1 levels remained cons tant in OC users (2.4 +/- 0.4, 2.6 +/- 0.4, and 2.4 +/- 0.4 pg/mL on days 1 to 3, 9 to 12, and 20 to 23 of the pill cycle). In contrast, ET-1 levels i n non-OC users decreased in all women during the follicular and luteal phas e of the menstrual cycle compared with the menstrual (low-estrogenic) phase (3.6 +/- 0.5, 2.8 +/- 0.5, and 2.9 +/- 0.3 pg/mL for the menstrual, follic ular, and luteal phase, respectively, P < .01 for menstrual v follicular an d P < .01 for menstrual v luteal). The differences between OC users and non users were significant in the menstrual phase of the cycle (P < .01). We co nclude that ET levels fluctuate during the menstrual cycle, Previously repo rted effects of the menstrual cycle on blood pressure may be partly explain ed by the effects of sex hormones on the level of vasoactive mediators. Thi s fluctuation is not present in OC users. Studies on hemodynamic parameters in premenopausal women should account for hormonal variations in the vario us phases of the menstrual cycle. Copyright (C) 2000 by W.B. Saunders Compa ny.