Prostaglandin D 2 (PGD 2 ) may act against myocardial ischemia-reperfusion (I/R) injury and play an anti-inflammatory role in the heart. Although the effect of PGD 2 in regulation of ANP secretion of the atrium was reported, the mechanisms involved are not clearly identified. The aim of the present study was to investigate whether PGD 2 can regulate ANP secretion in the isolated perfused beating rat atrium, and its underlying mechanisms. PGD 2 (0.1 to 10 µM) significantly increased atrial ANP secretion concomitantly with positive inotropy in a dose-dependent manner. Effects of PGD 2 on atrial ANP secretion and mechanical dynamics were abolished by AH-6809 (1.0 µM) and AL-8810 (1.0 µM), PGD 2 and prostaglandin F2α (PGF2α) receptor antagonists, respectively. Moreover, PGD 2 clearly upregulated atrial peroxisome proliferator-activated receptor gamma (PPARγ) and the PGD 2 metabolite 15-deoxy-Δ12,14-PGJ 2 (15d-PGJ 2 , 0.1 µM) dramatically increased atrial ANP secretion. Increased ANP secretions induced by PGD 2 and 15d-PGJ 2 were completely blocked by the PPARγ antagonist GW9662 (0.1 µM). PD98059 (10.0 µM) and LY294002 (1.0 µM), antagonists of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) signaling, respectively, significantly attenuated the increase of atrial ANP secretion by PGD 2 . These results indicated that PGD 2 stimulated atrial ANP secretion and promoted positive inotropy by activating PPARγ in beating rat atria. MAPK/ERK and PI3K/Akt signaling pathways were each partially involved in regulating PGD 2 -induced atrial ANP secretion.