Estrogen-induced increases in coronary blood flow are antagonized by inhibitors of nitric oxide synthesis

Abstract

Objective: Estrogen receptors have been found in coronary arterial endothelial and vascular smooth muscle cells. Therefore the present study was designed to determine if estradiol-17β can increase coronary blood flow and if so whether the changes are mediated by nitric oxide. Study design: Five oophorectomized non-pregnant sheep were chronically instrumented to measure blood pressure, heart rate, cardiac output, left circumflex coronary blood flow and central venous pressure. Animals received estradiol-17β (1.0 μg/kg) and cardiovascular responses were followed for 135 min. Results: Estradiol-17β (1.0 μg/kg) increased left circumflex (coronary) blood flow 28±3%, cardiac output 15±1% and heart rate by 13±3% Coronary vascular resistance decreased 23±5%, systemic vascular resistance decreased by 12±2% while blood pressure did not change significantly. Administration of the nitric oxide synthetase inhibitor l-nitroarginine methylester ( l-NAME), had no effect on basal coronary blood flow but completely reversed estradiol-17β induced increases in coronary blood flow. Conclusion: These results demonstrate that estrogen increases coronary blood flow in the non-pregnant sheep and that l-NAME, an inhibitor of nitric oxide, is able to reverse the estrogen induced flow changes.