This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Pharmacology, Subject name: Pharmacology
[{'content': 'Agonist drugs in high continuous doses causes: \nSelect and explain. \nA. Down regulation of receptors, B. Up regulation of receptors, C. Depends on dose, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans: a (Down regulation of receptors) Ref: Tripath 6th ed, p. 50Continuous receptor stimulation causes desensitization or refractoriness, the receptor becomes less sensitive to the agonist,e.g. bronchial asthma patients continously treated with beta-receptor agonists. This occurs by two mechanisms:1) Masking or internalization of the receptor2) Decreased synthesis/increased destruction of the receptor(Down regulation)', 'role': 'assistant'}]