Mechanisms responsible for endothelial dysfunction associated with acute estrogen deprivation in normotensive women

BACKGROUND: The goal of this study was to evaluate whether endothelial dysfunction associated with acute estrogen deprivation is caused by an alteration in the L-arginine-nitric oxide (NO) pathway and oxidative stress. Methods and Results-In 26 healthy women (age, 45.7+/-5.4 years) and 18 fertile women with leiomyoma (age, 44.5+/-5.1 years), we studied forearm blood flow (strain-gauge plethysmography) changes induced by intrabrachial acetylcholine (0. 15, 0.45, 1.5, 4.5, or 15 microgram. 100 mL(-1). min(-1)) or sodium nitroprusside (1, 2, or 4 microgram. 100 mL(-1). min(-1)), an endothelium-dependent or -independent vasodilator, respectively. The NO pathway was evaluated by repeating acetylcholine during L-arginine (200 microgram. 100 mL(-1). min(-1); 13 control subjects and 9 patients) or N(G)-monomethyl-L-arginine (L-NMMA; 100 microgram. 100 mL(-1). min(-1); 13 control subjects and 9 patients); production of cyclooxygenase-derived vasoconstrictors was assessed by repeating acetylcholine during indomethacin (50 microgram. 100 mL(-1). min(-1); 13 control subjects and 9 patients) or vitamin C (8 mg. 100 mL(-1). min(-1); 13 control subjects and 9 patients). Patients repeated the study within 1 month after ovariectomy and again after 3 months of estrogen replacement therapy (ERT; 17 beta-estradiol TTS, 50 microgram/d). Basally, vasodilation to acetylcholine was potentiated and inhibited by L-arginine and L-NMMA, respectively (P<0.05), but was unaffected by indomethacin or vitamin C. After ovariectomy, the modulating effect of L-arginine and L-NMMA disappeared, whereas indomethacin and vitamin C potentiated the response to acetylcholine (P<0.05). ERT restored L-arginine and L-NMMA effects on vasodilation to acetylcholine but prevented the potentiation caused by indomethacin or vitamin C. Response to sodium nitroprusside was unaffected by either ovariectomy or ERT. CONCLUSIONS: Endothelial dysfunction secondary to acute endogenous estrogen deprivation is caused by reduced NO availability. Cyclooxygenase-dependent production of oxidative stress could be responsible for this alteration.