**Core Concept**
Tolazoline is a vasodilator that acts as an alpha-2 adrenergic receptor antagonist, which leads to the relaxation of smooth muscle in blood vessels.

**Why the Correct Answer is Right**
Tolazoline works by blocking the alpha-2 adrenergic receptors on smooth muscle cells in blood vessels, preventing the vasoconstrictive effects of norepinephrine and increasing blood flow. This action is particularly useful in the treatment of peripheral vascular disease, where compromised blood flow can lead to ischemic symptoms. By increasing blood flow, tolazoline can help alleviate symptoms such as pain, coldness, and numbness in the affected limbs.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because tolazoline is not primarily used as a bronchodilator; its main action is on vascular smooth muscle.
**Option B:** Incorrect because tolazoline is not a direct-acting vasodilator like nitroglycerin; it works by blocking adrenergic receptors rather than directly relaxing smooth muscle.
**Option C:** Incorrect because tolazoline is not typically used in the treatment of hypertension; its use is more focused on peripheral vascular disease.

**Clinical Pearl / High-Yield Fact**
Tolazoline's vasodilatory effects can lead to a sudden increase in blood pressure in patients with severe hypertension, making it essential to monitor blood pressure closely when administering this medication.

**Correct Answer: C. Peripheral vascular disease.