**Core Concept**
Coronary vasodilation is a crucial physiological response to maintain cardiac perfusion, especially during periods of increased myocardial oxygen demand. This process is mediated by various factors, including metabolic byproducts, neural stimuli, and endothelial-derived relaxing factors.

**Why the Correct Answer is Right**
The primary mechanism of coronary vasodilation is the release of endothelium-derived relaxing factor (EDRF), now known as nitric oxide (NO). NO acts on the smooth muscle cells of the coronary arteries to increase the production of cyclic guanosine monophosphate (cGMP), leading to relaxation and vasodilation. This response is also influenced by the direct effect of oxygen radicals, such as superoxide anion, which can react with NO to form peroxynitrite, a potent vasodilator.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the primary mediator of coronary vasodilation.
**Option B:** This option is incorrect because while adenosine can cause vasodilation, it is not the primary mediator of coronary vasodilation in response to increased myocardial oxygen demand.
**Option C:** This option is incorrect because prostaglandins can cause vasodilation, but they are not the primary mediator of coronary vasodilation in this context.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the primary mediator of coronary vasodilation is nitric oxide, which is released from the endothelial cells in response to increased myocardial oxygen demand. This is a critical concept for understanding the pathophysiology of ischemic heart disease and the role of endothelial dysfunction in atherosclerosis.

**Correct Answer: B. Adenosine**