The two most well-studied cyclic nucleotides are cyclic AMP (cAMP) and cyclic GMP (cGMP), while cyclic CMP (cCMP) and cyclic UMP (cUMP) are less understood. cAMP is 3’5’-cyclic adenosine monophosphate, cGMP is 3’5’-cyclic guanosine monophosphate, cCMP is cytidine 3',5'-monophosphate, and cUMP is uridine 2',3'-cyclic phosphate.[4]