Endothelin-1 (ET-1) promotes lymphangiogenesis in vivo. Number, relative area, and size of lymphatic vessels (A) or blood vessels (B) in mouse skin overlying Matrigel plugs containing 1 μmol/L human ET-1 or PBS as vehicle control, two weeks after application of the plugs. Data represent mean ± SEM (n = 4). **P = 0.005. C: Representative micrographs of skin cross-sections from Matrigel plug assay, immunofluorescently stained for the lymphatic vessel marker LYVE-1 (green), the pan-vascular marker CD31 (red), and Hoechst nuclear dye (blue). Lymphatic vessels (yellow; CD31+/LYVE-1+) are indicated by white arrowheads. Single green cells represent CD31−/LYVE-1+ macrophages surrounding the Matrigel. S indicates skin; M, Matrigel plug. Scale bar = 100 μm.