Selective action of metoprolol to attenuate regadenoson-induced tachycardia in conscious dogs

Regadenoson is a coronary vasodilator that causes tachycardia via activation of the sympathetic nervous system. We determined whether β₁-adrenergic blockade can attenuate tachycardia without significantly reducing coronary vasodilation induced by regadenoson.

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.

β₁-Adrenergic blockade with metoprolol attenuated the regadenoson-induced increase in HR more than the increase in CBF.