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

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Abstract
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 .alpha.- and .beta.1- or combined .beta.1- and .beta.2-receptor blockade. NE, IP and PH did not alter CBP (112 .+-. 6 mm Hg). IP and PH did not affect HR (103 .+-. 4 beats/min). NE increased HR to 150 .+-. 6 beats/min, which was eliminated by blocking .beta.1-receptors with atenolol and by removing the left stellate ganglion. IP increased CBF from 65 .+-. 9 to 115 .+-. 16 ml/min (mediated by both .beta.1- and .beta.2-receptors). PH caused an .alpha.-receptor-mediated coronary vasoconstriction (42 .+-. 5 ml/min), which was potentiated by .beta.1- and .beta.2-receptor blockade. NE caused a biphasic flow response. CBF initially increased to 117 .+-. 14 ml/min (mediated predominantly by .beta.1-receptors) followed by a prolonged decrease to 54 .+-. 7 ml/min (mediated by .alpha.-receptors). Left stellate ganglion removal did not affect the CBF response to NE. Evidently, PH directly stimulates coronary .alpha.-receptors and IP stimulates myocardial .beta.1- and coronary .beta.2-receptors. NE also stimulates myocardial cells causing a reflex that increases HR and indirectly increases CBF. The vasoconstriction to NE and PH was no evident after pentobarbital anesthesia; the coronary vasodilation and increase in HR to NE was still present.