This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Autacoids, Subject name: Pharmacology
Bosentan is a/an: 
Select and explain. 
A. Serotonin uptake, B. Endothelin receptor antagonist, C. Leukotriene modifier, D. Phosphodiestease inhibitor
B: Endothelin receptor antagonist
Answer: B: Endothelin receptor antagonist 
Explanation: Endothelin receptors are of 2 types 1.ET A - in smooth muscles 2.ET B - in vascular endothelial cells BOSETAN , macicentan: endothelin receptor antagonists used for the treatment of pulmonary hypeension Ref: KD Tripathi 8th ed