BACKGROUND: Regadenoson is a coronary vasodilator that causes tachycardia via activation of the sympathetic nervous system. We determined whether β(1)-adrenergic blockade can attenuate tachycardia without significantly reducing coronary vasodilation induced by regadenoson. METHODS AND RESULTS: Hemodynamics and coronary blood flow (CBF) were measured in conscious dogs. Baseline CBF and heart rate (HR) were 42 ± 2 mL/min and 87 ± 8 bpm (mean ± SEM), respectively. Regadenoson (1, 2.5, and 5 μg/kg) increased peak CBF by 129 ± 10, 149 ± 7, and 174 ± 10 mL/min and HR by 48 ± 6, 67 ± 5, and 85 ± 11 bpm, respectively, (all P < .05 vs baseline). In the presence of metoprolol (1.5 mg/kg), the peak increases in CBF caused by these three doses of regadenoson were reduced by only 11 ± 7%, 10 ± 4%, and 21 ± 2% (P = NS, <.05, and <.05 vs regadenoson alone), respectively, whereas the regadenoson-induced tachycardia was significantly reduced by 55 ± 8%, 55 ± 4%, and 52 ± 5% (all P < .05). In the presence of metoprolol, the duration of the regadenoson-induced increase in CBF was reduced, but the duration of the 2-fold increase in CBF caused by 5 μg/kg regadenoson was still nearly 6 minutes. CONCLUSION: β(1)-Adrenergic blockade with metoprolol attenuated the regadenoson-induced increase in HR more than the increase in CBF.
BACKGROUND:Regadenoson is a coronary vasodilator that causes tachycardia via activation of the sympathetic nervous system. We determined whether β(1)-adrenergic blockade can attenuate tachycardia without significantly reducing coronary vasodilation induced by regadenoson. METHODS AND RESULTS: Hemodynamics and coronary blood flow (CBF) were measured in conscious dogs. Baseline CBF and heart rate (HR) were 42 ± 2 mL/min and 87 ± 8 bpm (mean ± SEM), respectively. Regadenoson (1, 2.5, and 5 μg/kg) increased peak CBF by 129 ± 10, 149 ± 7, and 174 ± 10 mL/min and HR by 48 ± 6, 67 ± 5, and 85 ± 11 bpm, respectively, (all P < .05 vs baseline). In the presence of metoprolol (1.5 mg/kg), the peak increases in CBF caused by these three doses of regadenoson were reduced by only 11 ± 7%, 10 ± 4%, and 21 ± 2% (P = NS, <.05, and <.05 vs regadenoson alone), respectively, whereas the regadenoson-induced tachycardia was significantly reduced by 55 ± 8%, 55 ± 4%, and 52 ± 5% (all P < .05). In the presence of metoprolol, the duration of the regadenoson-induced increase in CBF was reduced, but the duration of the 2-fold increase in CBF caused by 5 μg/kg regadenoson was still nearly 6 minutes. CONCLUSION: β(1)-Adrenergic blockade with metoprolol attenuated the regadenoson-induced increase in HR more than the increase in CBF.
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