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

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-17 beta 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-17 beta (1.0 mu g/kg) and cardiovascular responses were followed for 135 min. Results: Estradiol-17 beta (1.0 mu g/kg) increased left circumflex (coronary) blood flow 28+/-3%, cardiac output 15+/-1% and heart rate by 13+/-3%. Coronary vascular resistance decreased 231+/-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 Bow but completely reversed estradiol-17 beta 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. (C) 1997 Elsevier Science Ireland Ltd.