Hydrolyzes the second messenger cAMP, which is a key regulator of many important physiological processes. May be involved in specific signaling in the thyroid gland (By similarity). 3',5'-cyclic AMP + H2O = AMP + H(+) Binds 2 divalent metal cations per subunit. Site 1 may preferentially bind zinc ions, while site 2 has a preference for magnesium and/or manganese ions. Purine metabolism; 3',5'-cyclic AMP degradation; AMP from 3',5'-cyclic AMP: step 1/1. Widely expressed. Detectable in the adrenal gland of newborn animals. Composed of a C-terminal catalytic domain containing two putative divalent metal sites and an N-terminal regulatory domain. Belongs to the cyclic nucleotide phosphodiesterase family. PDE8 subfamily.