RESUMO
BACKGROUND: Prostaglandins (PGs), particularly prostaglandin D2 (PGD2), E2 (PGE2), and I2 (PGI2), are considered to play a role in migraine pain. In humans, infusion of PGD2 causes lesser headache as compared to infusion of PGE2 and PGI2. Follow-up studies in rats have shown that infusion of PGE2 and PGI2 dilate the middle meningeal artery (MMA), and mRNA for PGE2 and PGI2 receptors is present in rat trigeminovascular system (TVS) and in the brain structures associated with pain. In the present study, we have characterized the dilatory effect of PGD2 on rat MMA and studied the relative mRNA expression of PGD2 receptors and lipocalin-type of PGD2 synthase (L-PGDS). METHOD: Rat closed-cranial window (CCW) model was used to study the effect of the DP1 receptor antagonist, MK-0524, on PGD2-induced vasodilation of middle meningeal artery. The qPCR technique was used for mRNA expression analysis. RESULTS: PGD2 infusion evoked a dose-dependent dilation of the rat MMA. The calculated mean pED50 value was 5.23±0.10 and Emax was 103±18% (n=5). MK-0524 significantly (â¼61%, p<0.05) blocked the PGD2-induced dilation of MMA. mRNA for the DP1, DP2 and L-PGDS were expressed differentially in all tested tissues. DP1 receptor mRNA was expressed maximally in trigeminal ganglion (TG) and in cervical dorsal root ganglion (DRG). CONCLUSIONS: High expression of DP1 mRNA in the TG and DRG suggest that PGD2 might play a role in migraine pathophysiology. Activation of the DP1 receptor in MMA was mainly responsible for vasodilation induced by PGD2 infusion.