AJP - Heart and Circulatory Physiology, Vol 250, Issue 5 718-H724, Copyright © 1986 by American Physiological Society
Alpha-adrenoceptor subtypes and diltiazem actions in isolated human coronary arteries
N. Toda
Isolated human, monkey, and dog coronary arteries treated with propranolol
responded to norepinephrine with concentration-related contractions; the
magnitude was in the order of human greater than monkey greater than dog
arteries. Phenylephrine also contracted these arteries, whereas clonidine
produced contractions only in the primate arteries. Contractile responses
of human coronary arteries to norepinephrine were not influenced by removal
of endothelium. Norepinephrine-induced contractions of human and monkey
coronary arteries were attenuated by prazosin and yohimbine in a
dose-dependent manner; however, the amine-induced contractions of dog
coronary arteries were attenuated only by prazosin. Diltiazem, a Ca2+
antagonist, relaxed human and dog coronary arteries contracted with
norepinephrine to a similar extent, but produced a greater relaxation in
the human arteries when partially contracted with prostaglandin F2 alpha.
These findings suggest that alpha 1- and alpha 2-adrenoceptors are involved
in the amine-induced contraction in human and monkey coronary arteries,
whereas only alpha 1-receptors are involved in dog artery contraction.
Human coronary artery contractions induced by norepinephrine do not appear
to be more susceptible to Ca2+ antagonists than the dog artery
contractions, which does not provide evidence supporting the hypothesis
that Ca2+ antagonists interfere with contractions mediated by alpha
2-receptors to a greater extent than those mediated by alpha 1-receptors in
large human coronary arteries.
