1. To investigate the effects of acute β1-adrenoceptor blockade on sympathetic nervous activity, cardiac and whole-body noradrenaline kinetics were determined during intravenous infusions of saline placebo and of metoprolol (10-15 mg plus 150 μg min−1 kg−1) in 10 patients undergoing diagnostic cardiac catheterization, in whom β-adrenoceptor antagonists had been discontinued for 7 days.

2. Coronary haemodynamics were measured in these 10 patients plus two others. Compared with saline placebo, metoprolol administration was associated with decreases in heart rate (68 ± 2 to 59 ± 3 beats/min, P < 0.001) and coronary sinus blood flow (86 ± 8 to 68 ± 6 ml/min, P < 0.001) and an increase in calculated coronary vascular resistance (1.42 ± 0.19 to 1.75 ± 0.22 mmHg min ml−1, P < 0.001). Arterial and femoral venous noradrenaline concentrations, whole-body noradrenaline clearance and whole-body noradrenaline spillover to arterial plasma did not change. In contrast, cardiac noradrenaline spillover (33.7 ± 5.1 to 20.2 ± 4.3 pmol/min, P < 0.05) and cardiac noradrenaline clearance (31 ± 3 to 23 ± 3 ml/min, P < 0.001) were significantly decreased during metoprolol administration.

3. These results may be explained by inhibition of pre-junctional facilitatory β-adrenoceptors, which we hypothesize may be predominantly of the β1-subtype in the heart and of the β2-subtype in the periphery.

This content is only available as a PDF.
You do not currently have access to this content.