Consider this pathway: epinephrine → g protein-coupled receptor → g protein → adenylyl cyclase → camp. identify the second messenger.

The second messenger is cAMP. The cyclic adenosine monophosphate or as called as cAMP is an activator of phosphorylase kinase and an effector of other enzymes made in muscle from ATP by adenylate cyclase and broken down to 5' AMP by a phosphodiesterase which is the first known second messenger and a regulator of metabolism.