ABSTRACT
Coronary blood flow is determined by a complex integration of several factors including myocardial metabolism, cardiac compressive forces, coronary perfusion pressure, concentrations of humoral and locally produced vasoactive agents, and autonomic activity. The dense sympathetic innervation of coronary vessels and prominent vasoconstrictor response observed during neural activation suggest an important role for neurally mediated vasoconstriction in the physiological regulation of coronary blood flow. Muscarinic cholinergic receptors are present on canine coronary arterial smooth muscle, and on adjacent intimal endothelial cells. The presence of significant coronary flow reserve allows metabolic vasodilation to effectively compete with vasoconstrictor stimuli. Stimulation of the vagus nerves produces a profound decrease in heart rate, a fall in arterial pressure, and a decrease in coronary blood flow. Reducing mean carotid arterial pressure produces a well-characterized reflex increase in sympathetic outflow to the heart that includes tachycardia, inotropic stimulation, and activation of coronary adrenergic receptors.
