Cyclic nucleotide phosphodiesterases (PDEs) include a large group of structurally related enzymes that are responsible for the hydrolysis of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). These enzymes belong to at least nine related gene families (PDEs 1–9) (1 –5 ), which differ in their primary structures, affinities for cAMP and cGMP, responses to specific effectors, sensitivities to specific inhibitors, and regulatory mechanisms. ThePDE3family (6 ) consists of two subfamilies,PDE3AandPDE3B, which exhibit tissue-specific distribution; grossly,PDE3Aenzymes are expressed in the cardiovascular system, and PDE3B enzymes in insulin-sensitive cells, such as hepatocytes (7 ) and adipocytes (6 ), and also in pancreatic β-cells (8 ). One characteristic of PDE3s involves their phosphorylation and activation in response to insulin, as well as to agents that increase cAMP in adipocytes (6 ), hepatocytes (7 ), and platelets (9 –11 ), and in response to insulin-like growth factor-1 (IGF-)1 in pancreatic β-cells (8 ).
