Contractile Responses to Histamine, Serotonin, and Angiotensin II Are Impaired by 17β-Estradiol in Human Internal Mammary Arteries in vitro

There is accumulating evidence that estrogen replacement therapy protects against the development of coronary atherosclerosis and myocardial infarction in postmenopausal women. The mechanism of this protective effect is uncertain. The purpose of the present study was to determine whether 17β-estradiol acutely modifies vascular smooth muscle contractile responses to various agonists in human arteries in vitro. Human mammary artery rings were obtained during aortocoronary bypass operations. Rings were suspended in organ baths for isometric tension measurements. Concentration response curves induced by serotonin (0.01–30 µmol/l), histamine (0.01–300 µmol/l), and angiotensin II (0.1–100 nmol/l) were generated after pre-incubation for 30 min with either 17β-estradiol (3 µmol/l) or solvent (0.2% ethanol). The presence of 17β-estradiol significantly reduced the maximal contractile effects induced by histamine, serotonin, and angiotensin II, but not by 80 mmol/l potassium chloride. It is concluded that short-term incubation with 17β-estradiol reduces the maximal contractile reponses to serotonin, histamine, and angiotensin II. These modulating effects of estrogen on vascular tone may contribute to the proposed beneficial role of estrogen replacement therapy on the incidence of myocardial infarction in postmenopausal women.