**Core Concept**
Nitroglycerin, a nitrate medication, is used for the treatment of acute chest pain, primarily due to its vasodilatory effects on the coronary arteries. This action helps to reduce myocardial oxygen demand by decreasing both preload and afterload.

**Why the Correct Answer is Right**
Sublingual nitroglycerin works by releasing nitric oxide, which activates guanylyl cyclase in vascular smooth muscle cells. This leads to an increase in cyclic guanosine monophosphate (cGMP) levels, causing smooth muscle relaxation and subsequent vasodilation. The primary vasodilatory effect is on the venous capacitance vessels, which reduces preload. This decrease in preload subsequently reduces the wall tension, thereby reducing the oxygen demand of the myocardium.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not directly related to the action of nitroglycerin. While hypotension can be a side effect, it's not the primary concern in the context of acute chest pain treatment.
**Option B:** Nitroglycerin does not directly affect the inflammatory response. Its mechanism is centered on vasodilation and reducing myocardial oxygen demand.
**Option C:** This is a potential side effect, but not the most direct or relevant consequence of using sublingual nitroglycerin for acute chest pain.

**Clinical Pearl / High-Yield Fact**
Nitroglycerin is contraindicated in patients with hypotension, heart failure, or those who have taken phosphodiesterase inhibitors (e.g., sildenafil) within the past 24 hours.

**Correct Answer: C. Headache.**