Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a major cause of end-stage kidney disease in man. The central role of cyclic adenosine monophosphate (cAMP) in ADPKD pathogenesis has been confirmed by numerous studies including positive clinical trial data. Here, we investigated the potential role of another major regulator of renal cAMP, prostaglandin E2?(PGE2), in modifying disease progression in ADPKD models using selective receptor modulators to all four PGE2?receptor subtypes (EP1-4). In 3D-culture model systems utilizing dog (MDCK) and patient-derived (UCL93, OX161-C1) kidney cell lines, PGE2?strikingly promoted cystogenesis and inhibited tubulogenesis by stimulating proliferation while reducing apoptosis. The effect of PGE2?on tubulogenesis and cystogenesis in 3D-culture was mimicked or abolished by selective EP2 and EP4 agonists or antagonists but not those specific to EP1 or EP3. In a?Pkd1?mouse model (Pkd1nl/nl), kidney PGE2?and COX-2 expression were increased by two-fold at the peak of disease (week four). However,?Pkd1nl/nl?mice treated with selective EP2 (PF-04418948) or EP4 (ONO-AE3-208) antagonists from birth for three weeks had more severe cystic disease and fibrosis associated with increased cell proliferation and macrophage infiltration. A similar effect was observed for the EP4 antagonist ONO-AE3-208 in a second?Pkd1?model (Pax8rtTA-TetO-Cre-Pkd1f/f). Thus, despite the positive effects of slowing cyst growth?in?vitro, the more complex effects of inhibiting EP2 or EP4?in?vivo?resulted in a worse outcome, possibly related to unexpected pro-inflammatory effects.