Sympathetic regulation of coronary circulation during handgrip exercise and isolated muscle metaboreflex activation in men

New Findings What is the central question of this study? What is the role of beta- and alpha-adrenergic receptors in the control of the coronary circulation during handgrip exercise and isolated muscle metaboreflex activation in humans? What is the main finding and its importance? beta-Adrenergic receptor, but not alpha-adrenergic receptor, blockade significantly blunted the increases in coronary blood velocity observed during handgrip. Coronary blood velocity was unchanged from baseline during isolated muscle metaboreflex activation. This highlights the important role of beta-adrenergic receptors in the coronary circulation during handgrip in humans, and the more limited involvement of the alpha-adrenergic receptors. We sought to investigate the role of beta- and alpha-adrenergic receptors in coronary circulation during static handgrip exercise and isolated muscle metaboreflex activation in humans. Seventeen healthy young men underwent two experimental sessions, consisting of 3 min of static handgrip exercise at a target force of 40% maximum voluntary force (not achieved for the full 3 min), and 3 min of metaboreflex activation (post-exercise ischaemia) in two conditions: (1) control and beta-blockade (oral propranolol), and (2) control and alpha-blockade (oral prazosin). In both sessions, coronary blood velocity (CBV, echocardiography) was increased during handgrip (Delta 8.0 +/- 7.4 cm s(-1)) but unchanged with metaboreflex activation (Delta 2.5 +/- 3.2 cm s(-1)) under control conditions. beta-Blockade abolished the increase in CBV during handgrip, while CBV was unchanged from control with alpha-blockade. Cardiac work, estimated from rate pressure product (RPP; systolic blood pressure multiplied by heart rate), increased during handgrip and metaboreflex in control conditions in both sessions. beta-Blockade reduced RPP responses to handgrip and metaboreflex, whereas alpha-blockade increased RPP, but the responses to handgrip and metaboreflex were unchanged. CBV and RPP were only significantly correlated during handgrip under control (r = 0.71, P < 0.01) and beta-blockade (r = 0.54, P = 0.03) conditions, and the slope of this relationship was unaltered with beta-blockade. Collectively, these findings indicate that beta-adrenergic receptors play the primary role to the increase of coronary circulation during handgrip exercise, but CBV is unchanged with metaboreflex activation, while alpha-adrenergic receptor stimulation seems to exert no effect in the control of the coronary circulation during handgrip exercise and isolated muscle metaboreflex activation in humans.

Automated summary

The study found that beta-adrenergic receptors play a primary role in increasing coronary circulation during handgrip exercise in humans, while coronary blood velocity remains unchanged during metaboreflex activation. The involvement of alpha-adrenergic receptors seems to have limited impact on the control of coronary circulation during handgrip exercise and isolated muscle metaboreflex activation.