The second messengers cyclic AMP and cyclic GMP
Activate the same signal transduction pathways
Are generated by the activation of cyclases
Activate the same protein kinase
Are impoant only in sensory transduction
The cAMP is called a second messenger because it is not the hormone itself that directly institutes the intracellular changes; instead, the cAMP serves as a second messenger to cause these effects.For a few peptide hormones, such as the atrial natriuretic peptide, cyclic guanosine monophosphate, which is only slightly different from cAMP, serves in a similar manner as a second messenger.Adenylyl Cyclase-cAMP Second Messenger SystemStimulation of adenylyl cyclase, a membrane-bound enzyme, by the Gs protein then catalyzes the conversion of a small amount of cytoplasmic adenosine triphosphate into cAMP inside the cell. This then activates cAMP-dependent protein kinase, which phosphorylates specific cell proteins, triggering biochemical reactions that ultimately lead to the cell's response to the hormone.Ref: Guyton; 13th edition; Chapter 75; Introduction to Endocrinology
General physiology