Autonomic control of large coronary arteries and resistance vessels.

The resistance coronary vessels as well as the large coronary arteries are regulated to a major extent by autonomic mechanisms. Neural and pharmacologic activation of alpha-adrenergic pathways can reduce coronary blood flow and the cross-sectional area of large coronary arteries, despite concomitant increases in coronary distending pressure. Activation of either beta 1- or beta 2-adrenergic receptors can induce potent dilation of both coronary resistance vessels and large coronary arteries, whereas blockade of these receptors can elicit profound constriction in the presence of elevated beta-adrenergic tone. The regulation of the coronary circulation by parasympathetic mechanism remains the most controversial, likely because of major species differences. Parasympathetic coronary dilation is uniformly observed in the dog, but in primates, important aspects of parasympathetic-mediated coronary vasoconstriction have also been demonstrated.