AJP - Heart and Circulatory Physiology, Vol 250, Issue 4 645-H653, Copyright © 1986 by American Physiological Society
Adrenergic vasoconstriction lessens transmural steal during coronary hypoperfusion
H. J. Nathan and E. O. Feigl
The hypothesis that alpha-receptor-mediated coronary vasoconstriction can
lessen transmural steal during hypoperfusion was tested in 14 open-chest,
chloralose-anesthetized dogs. Coronary flow to two regions of the left
ventricle was controlled by separately cannulating and pump perfusing the
anterior descending and circumflex coronary arteries. An intracoronary
infusion of the alpha-receptor blocking agent phenoxybenzamine (0.25 mg/kg)
was administered to one region while coronary sinus blood flow was trapped
to minimize recirculation. All animals received atropine (0.5 mg/kg) and
propranolol (2 mg/kg) intravenously. alpha-Receptor activation in both
regions of the left ventricle was achieved with an intracoronary infusion
of norepinephrine. Radioactive microspheres were used to measure the
transmural distribution of myocardial blood flow as coronary flow in the
paired regions was reduced from 100 to 80, 70, 60, and 50% of normal. When
total coronary flow was reduced sufficiently to cause ischemia and
maldistribution of flow across the myocardial wall, the subendocardial
blood flow was greater in the alpha-receptor-intact region than in the
alpha-blocked region. This indicates that alpha-receptor-mediated coronary
vasoconstriction has an unexpected beneficial effect that lessens
transmural steal during hypoperfusion.
