Coronary blood flow changes following activation of adrenergic receptors in the conscious dog

The role of coronary vascular adrenergic receptors in changing coronary flow was studied in dogs instrumented to measure left circumflex artery blood flow (CBF), mean coronary artery blood pressure (CBP), and heart rate (HR). Norepinephrine (NE), isoproterenol (IP), and phenylephrine (PH) were injected into the left circumflex artery before and after selective intracoronary α- and β₁- or combined β₁- and β₂-receptor blockade. NE, IP, and PH did not affect CBP (112 ± 6 mm Hg). In addition, IP and PH did not affect HR (103 ± 4 beats/min). NE increased HR to 150 ± 6 beats/min, which was eliminated by blocking β₁-receptors with atenolol and by removing the left stellate ganglion. IP increased CBF from 65 ± 9 to 115 ± 16 ml/min (mediated by both β₁ and β₂-receptors). PH caused an α-receptor-mediated coronary vasoconstriction (42 ± 5 ml/min), which was potentiated by β₁- and β₂-receptor blockade. NE caused biphasic flow response. CBF initially increased to 117 ± 14 ml/min (mediated predominantly by β₁-receptors) followed by a prolonged decrease to 54 ± 7 ml/min (mediated by α-receptors). Removing the left stellate ganglion did not affect the CBF response to NE. These data indicate that PH directly stimulates coronary α-receptors and IP stimulates myocardial β₁- and coronary β₂-receptors. NE also stimulates myocardial cells causing a reflex that increases HR and indirectly increases CBF. The vasoconstriction to NE and PH was not evident after pentobarbital anesthesia, whereas the coronary vasodilation and increase in HR to NE was still present.