Desensitisation is the loss of responsiveness to the continuing or increasing dose of a drug.
Receptor desensitisation occurs after prolonged or repeated exposure to a stimulus and often results in decreased responsiveness of that receptor for a stimulus. Receptor desensitisation also results in altered affinity for the ligand. Desensitisation may be accomplished byreceptor phosphorylation, uncoupling of receptor effector molecules and receptor internalisation as illustrated by the following example:
In the late response phase (hours), the receptors are decreased too due to internalisation. Similarly as the second messenger, the receptor density can be restored by washing out the isoprenaline.