Objectives: Oestrogen has been shown to increase nitric oxide-mediated vasodilatation and modulate sympathetic tone in postmenopausal women. We investigated the acute effects of oestrogen on the coronary microcirculation in men.
Methods: Myocardial blood flow was quantified using N-ammonia positron emission tomography before and 20 min after an intravenous administration of conjugated oestrogen (10 mg) in nine healthy men.
Results: There were no significant changes in either systemic blood pressure or heart rate before and after oestrogen infusion. However, myocardial blood flow was increased by oestrogen from 0.88 +/-0.06 to 1.05+/-0.09 ml x g x min (P<0.05). Although serum levels of nitrite/nitrate (end products of nitric oxide) were not increased, circulating norepinephrine (noradrenaline) levels were decreased after the administration of oestrogen from 401+/-114 to 346+/-112 pg x ml (P<0.01). A significant negative correlation was found between myocardial blood flow and plasma norepinephrine levels (r=-0.67, P<0.05).
Conclusions: A single administration of oestrogen enhanced myocardial circulation in healthy men. The oestrogen-induced increase in myocardial blood flow may be due to direct effects on the coronary circulation or through the modulation of norepinephrine levels, rather than the production of nitric oxide.