Final answer:
Adenosine and prostaglandins act on vascular smooth muscle to cause vasodilation when the myocardium has increased levels of carbon dioxide.
Step-by-step explanation:
Adenosine and prostaglandins act on vascular smooth muscle to cause vasodilation when the myocardium has increased levels of carbon dioxide. Vasodilation is the widening of the lumen of blood vessels, allowing increased blood flow and reducing resistance in the arteries. This helps to regulate blood pressure. It is important to note that adenosine and prostaglandins have other functions as well, but in this context, they act to cause vasodilation in response to increased carbon dioxide levels.