beta-Adrenergic receptor blockade impairs coronary exercise hyperemia in young men but not older men

摘要

Patients with coronary artery disease have attenuated coronary vasodilator responses to physiological stress, which is partially attributed to a beta-adrenergic receptor (beta-AR)-mediated mechanisms. Whether beta-ARs contribute to impaired coronary vasodilation seen with healthy aging is unknown. The purpose of this study was to investigate the role of beta-ARs in coronary exercise hyperemia in healthy humans. Six young men (26 ?1 yr) and seven older men (67 ?4 yr) performed isometric handgrip exercise at 30% maximal voluntary contraction for 2 min after receiving intravenous propranolol, a beta-AR antagonist, and no treatment. Isoproterenol, a beta-AR agonist, was infused to confirm the beta-AR blockade. Blood pressure and heart rate were monitored continuously, and coronary blood flow velocity (CBV, left anterior descending artery) was measured by transthoracic Doppler echocardiography. Older men had an attenuated ACBV to isometric exercise (3.8 ?.3 vs. 9.7 ?.1 cm/s, P = 0.02) compared with young men. Propranolol decreased the ACBV at peak handgrip exercise in young men (9.7 ?2.1 vs..2.7 ?0.9 cm/s, P = 0.008). However, propranolol had no effect on ACBV in older men (3.8 ?1.3 vs. 4.2 ?1.9 cm/s, P = 0.9). Older men also had attenuated coronary hyperemia to low-dose isoproterenol. These data indicate that beta-AR control of coronary blood flow is impaired in healthy older men.