17β-Estradiol Inhibits Ca2+ Influx and Ca2+ Release Induced by Thromboxane A2 in Porcine Coronary Artery

Background We wished to investigate the possible mechanism of the protective effect of estrogen replacement on coronary atherosclerosis observed in postmenopausal women. Methods and Results Cytosolic Ca2+ concentration ([Ca2+]i) and contraction were measured simultaneously in fura 2–loaded porcine coronary arterial strips stimulated by the thromboxane A2 analogue U46619 and high-K+ depolarization in the presence and absence of 17β-estradiol. Pretreatment with 17β-estradiol (30 nmol/L to 30 μmol/L) inhibited the sustained elevation of [Ca2+]i and the sustained contraction induced by 300 nmol/L U46619. Higher concentrations of 17β-estradiol (1 to 100 μmol/L) also inhibited the U46619-induced transient increase in [Ca2+]i and contraction in the absence of extracellular Ca2+. In the strips precontracted by 90 mmol/L K+, 17β-estradiol (30 μmol/L) inhibited the increases in [Ca2+]i and contraction to resting levels. In contrast, 30 μmol/L 17β-estradiol only partially inhibited the U46619-induced sustained contr...