This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System Pa 1, Subject name: Physiology
[{'content': 'Most potent vasoconstrictor of the pulmonary aery is: \nSelect and explain. \nA. Endothelin, B. Hypoxia, C. Angiotensin, D. TXA2', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Endothelin, urotensin, angiotensin are the potent constrictors of the systemic vessels. In case of the pulmonary vessels, hypoxia is the strongest vasoconstrictor, acting the O2-sensitive K+ channels in the pulmonary vascular smooth muscle cells (VSMCs).', 'role': 'assistant'}]