Which substances are main regulators of coronary blood flow?

• A. O2, CO2, Adenosine, NO
• B. O2, CO2, Adenosine, Lactate
• C. O2, CO2, NO, Epinephrine
• D. Adenosine, NO, Lactate, K+

Answer: (A)

Coronary blood flow is matched to the heart’s metabolic needs by local signals from the tissues and the endothelium. When the myocardium is active, adenosine is produced from ATP breakdown and acts on vascular smooth muscle to cause robust vasodilation, increasing flow to meet demand. A drop in oxygen tension itself also promotes dilation, signaling the need for more oxygen delivery. At the same time, increased metabolic activity raises CO2 levels, which stimulates vasodilation of the coronary vessels. Nitric oxide, released from endothelial cells in response to shear stress and other stimuli, further relaxes smooth muscle and widens the vessels. Together, oxygen, carbon dioxide, adenosine, and NO are the main local regulators that tune coronary perfusion to myocardial workload.

Lactate and potassium can influence vascular tone, and epinephrine can modulate tone via receptors, but they are not the primary regulators of coronary blood flow in the resting-to-active range.