What is desensitization of receptors?

Prolonged exposure to the catecholamines reduces the responsiveness of these receptors Three mechanisms have been suggested to explain this phenomenon: sequestration of the receptors so that they are unavailable for interaction with the ligand; down-regulation: disappearance of the receptors either by destruction or decreased synthesis; an inability to couple to G protein, because the receptor has been phosphorylated on the cytoplasmic side