**Core Concept**
Bosentan is an endothelin receptor antagonist used in the treatment of pulmonary arterial hypertension (PAH). It works by blocking the action of endothelin-1, a potent vasoconstrictor, thereby improving exercise capacity and symptoms in patients with PAH.

**Why the Correct Answer is Right**
Bosentan is unique among endothelin receptor antagonists as it is a dual endothelin receptor antagonist, acting on both ETA and ETB receptors. This dual action contributes to its efficacy in treating PAH. Bosentan also undergoes extensive hepatic metabolism, primarily by CYP2C9 and CYP3A4 enzymes.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is true about bosentan. It is indeed a dual endothelin receptor antagonist.
**Option B:** This statement is true about bosentan. It is used in the treatment of pulmonary arterial hypertension (PAH).
**Option C:** This statement is false about bosentan. It is not a vasopressor; rather, it is a vasodilator.

**Clinical Pearl / High-Yield Fact**
Bosentan is one of the first dual endothelin receptor antagonists approved for the treatment of PAH, and its unique mechanism of action makes it a valuable addition to the therapeutic arsenal for this disease.

**Correct Answer: C. It is not a vasopressor; rather, it is a vasodilator.**