Postsynaptic α2 adrenoceptors in coronary artery and its role in sympathetic induced vasoconstriction

Study was carried out in 37 anesthetized dogs with left circumflex coronary cannulated and perfused by peristalic pump. The coronary artery responsed to both alpha 1 and 2 agonists with vasoconstriction. The response to azepexole (alpha 2 agonist) was resistant to prazosin. After beta blockade, norepinephrine and epinephrine produced dose related increase of coronary perfusion pressure which was not remarkedly reduced by prazosin but significantly blunted after yohimbine or idazoxan. Left stellate ganglionic electric stimulation induced frequency related increase of coronary pressure which was partially-prevented by prazosin； while idazoxan almost totally abolished the response. These studies show that the postsynaptic alpha 2 adrenoceptors exist in coronary arteries and its important role in mediating the vasoconstriction response produced by both electric sympathetic nerve stimulation and circulating catecholamines.