<prompt> Agonist drugs in high continuous doses causes:Down regulation of receptorsUp regulation of receptorsDepends on doseNone  <response>: 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 synthesisincreased destruction of the receptorDown regulation 