Immunohistochemical detection of EP3 and EP4 receptor proteins in rat growth plates and in cultured chondrocytes. Protein expression of EP3 and EP4 receptor was studied in growth plate tissue and cultured chondrocytes using isoform-specific antibodies. The EP3 and EP4 receptors were distributed throughout the whole growth plate. Cultured chondrocytes exhibited only weak reactivity towards the anti-EP antibodies. Only a minor subpopulation of cells showed strong staining for EP3 receptor and EP4 receptor. Magnification: 200 × . r, reserve zone; p, proliferative zone; h, hypertrophic zone.