Relative expression of EP 1, 2, 3 and 4 receptors mRNA in lung tissue assayed by real-time PCR. Graphs a, b, c, and d show the mRNA expression of the EP1, EP2, EP3, and EP4 receptors, respectively, in the different treatment groups. EP receptor mRNA expression was higher for all four receptors in HDM-sensitized mice (n = 11) than in non-sensitized animals (n = 5), but only EP2 showed a significant allergen-induced upregulation (4.6 fold). Treatment with either agonist (PGE2 or sulprostone) did not significantly alter the level of expression of lung EP1, 3, and 4 in non-sensitized (n = 5) or HDM-sensitized mice (n = 11). However, sulprostone, but not PGE2, induced a 3.5-fold increased expression of EP2 baseline levels (non-sensitized mice), and it then prevented HDM from further enhancing these levels (*p < 0.05, **p < 0.01).