Fig. 2. Vessel morphology in mouse tissues after treatment with angiopoietin 1. Mouse pups were treated daily for 7 days with 200 µg of ANG1^4FD protein. Arteries and veins were readily identified in wholemounts by virtue of the differential coating of the smooth muscle cell layer (arterioles had a regular layer of elongated smooth muscle cells wrapped circumferentially around the vessels, whereas venules had an irregular layer of spread, branched smooth muscle cells associated with the vessels) and by vessel morphology (arteries were straighter and smaller in diameter than the corresponding veins). (A,B) Whole-mount views of tracheas from P14 mice, with blood vessels immunostained for PECAM (green) and -smooth muscle cell actin (red/orange). The straight capillaries traverse the cartilaginous rings. The venular ends of the capillaries are enlarged in the tracheas of ANG1^4FD-treated mice (arrows, B) compared with PBS controls (A), and the draining venules are also enlarged, whereas the arterioles (arrowheads) are not enlarged. (C,D) Cross-sections of tongue from P14 mice, with blood vessels immunostained for PECAM (green) and -smooth muscle cell actin (red/orange). The upper epidermal surface of the tongue is at the upper part of the image. The draining venules and the vessel loops in the dermal papillae (arrows) in the muscosa and muscle layers are enlarged in the tongues of ANG1^4FD-treated mice (D) compared with PBS controls (C). By contrast, the feeding arterioles (arrowheads) are similar in size in both ANG1^4FD-treated and control mice. (E,F) Whole-mount views of diaphragm from P14 mice, with blood vessels immunostained for PECAM (green) and -smooth muscle cell actin (red/orange). The straight capillaries are in the skeletal muscle and the draining venules (arrows) are at the boundary with the central tendon. The venules (arrows) in the central tendon are enlarged in the diaphragms of ANG1^4FD-treated mice (F) compared with PBS controls (E). By contrast, the muscle capillaries in ANG1^4FD-treated mice and control mice are similar in size. (G,H) Whole-mount views of retinas from P14 mice, with blood vessels stained with Griffonia simplicifolia isolectin B4 (green). The capillaries traverse between arterioles (arrowheads) and venules (arrows). The venular networks (arrows) are enlarged in retinas of ANG1^4FD-treated mice (H) compared with PBS controls (G).