Cyclic adenosine monophosphate is needed to carry messages from the cell surface to the nucleus. External signals, such as hormones like adrenaline, are not allowed to pass through the plasma membrane of the cell. cAMP relays the message from the receptor on the cell surface, through the cytoplasm, and into the nucleus of the cell through signal transduction. cAMP may also assist ions as they pass through the cell membrane through ion channels.