Cyclic AMP-dependent phosphodiesterase type D (PDE4D) family is comprise of 5 variants (PDE4D1, D2, D3, D4 and D5). One or more PDE4D subtype variants are ubiquitously present in all mammalian cells. In CNS all five PDE4D subtype variants are expressed in varying ratios and their activity is regulated in tandem with GPCRs stimulation. Peripheral tissues also exhibit differential expression of PDE4D variants. PDE4D1/D2 mRNA levels rise in response to an increase in cAMP. Short term regulation of PDE4D variants involved PKA, MAP kinases and Erk2 phosphorylation that results in rapid change in their enzymatic activities. Other regulatory mechanism involved protein protein interactions with cytoskeletal scaffolding proteins.