Most appropriate regarding regulation of coronary circulation is:

All options are regulator of coronary circulation but the most important one is autoregulation. Blood flow increases when the metabolism of the myocardium is increased. The caliber of the coronary vessels, and consequently the rate of coronary blood flow, is influenced not only by pressure changes in the aorta but also by chemical and neural factors. The coronary circulation also shows considerable autoregulation. The close relationship between coronary blood flow and myocardial O2 consumption indicates that one or more of  the products of metabolism cause coronary vasodilation. The coronary arterioles contain α-adrenergic receptors, which mediate vasoconstriction, and β-adrenergic receptors, which mediate vasodilation. Activity in the noradrenergic nerves to the heart and injections of norepinephrine cause coronary vasodilation. The direct effect of noradrenergic stimulation is constriction rather than dilation of the coronary vessels.    Reference: Ganong’s Review of Medical Physiology T W E N T Y - F I F T H   E D I T I O N page no 612