PDE5A and hydrops fetalis: Supporting this mechanism, Schobesberger et al. further confirmed the localization of β3-ARs in the caveolae and the related cGMP pools in the T-tubules, which are locally regulated mostly by PDE2 and PDE5 [109], and stimulation by NO-donor after β-AR-stimulation further decreased global cAMP levels in HF [134].