The adenosine A1 receptor antagonist naphthyridine inhibits VEGFA-induced angiogenesis and lymphatic vessel enlargement in mice. VEGFA-containing Matrigel plugs were implanted subcutaneously into adult mice, and the mice were subsequently treated systemically with naphthyridine or with vehicle control for 6 days. (A-C) Differential immunofluorescence analysis for the lymphatic-specific marker LYVE1 (green, examples highlighted by arrows) and the pan-vascular marker CD31 (red) demonstrated lymphatic vessel enlargement and enhanced numbers of blood vessels in the skin surrounding VEGFA-containing Matrigels (B), compared with Matrigels containing PBS (A). Treatment with naphthyridine resulted in a reduction of blood vessel numbers and lymphatic vessel enlargement (C). (D-G) Quantitative image analyses confirmed that the density of lymphatic vessels was unchanged by VEGFA alone or by combined VEGFA and naphthyridine treatment (D). In contrast, the tissue area covered by lymphatic vessels surrounding VEGFA-containing Matrigels was significantly reduced by treatment with naphthyridine (E). Treatment with naphthyridine also reduced the number of VEGFA-induced blood vessels (F) and the tissue area covered by blood vessels (G). Scale bars represent 100 μm.