Agonist drugs in high continuous doses causes:: (A) Down regulation of receptors, (B) Up regulation of receptors, (C) Depends on dose, (D) None
Answer is A. 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)