Hormone which have to interact with membrane bound receptor, do not bind itself for that it require secondary messenger like (cAMP) whichact as intracellular hormonal mediator which diliver the information inside the target cell. It activate the appropriate cellular enzyme system where the specific hormone stimulated responses takes place. Secondary messenger are cAMP, cGMP, diacyglycerol, inositoltriphosphate, phospoinositides, calcium etc.