Oestrogen increases myocardial blood flow in men:: assessment by 13N-ammonia positron emission tomography

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-13-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 g(-1) min(-1) (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 ml(-1) (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. Nucl Med Commun 25:557-562 (C) 2004 Lippincott Williams Wilkins.