AJP - Heart and Circulatory Physiology, Vol 243, Issue 1 13-H19, Copyright © 1982 by American Physiological Society
Coronary blood flow changes following activation of adrenergic receptors in the conscious dog
P. A. Gwirtz and H. L. Stone
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 mmHg). 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 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). Removing the left stellate ganglion did not affect the
CBF response to NE. These data indicate that 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 not evident after pentobarbital anesthesia, whereas the coronary
vasodilation and increase in HR to NE was still present.
