PDE8a (high affinity cAMP-specific and IBMX-insensitive 3´,5´-cyclic phosphodiesterase 8 A) is a cyclic nucleotide phosphodiesterase, which hydrolyzes cAMP, an important regulator and mediator of multiple cellular responses to extracellular signals. It is expressed in a wide variety of tissues including testis, ovary, small intestine, and colon. It is not expressed e.g. in thymus. PDE8a is composed of C-terminal catalytic domain containing two putative divalent metal sites and an N-terminal regulatory domain.