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To gain insight into how a naturally occurring scaffold composed of extracellular matrix (ECM) proteins provides directional guidance for capillary sprouting, we examined angiogenesis in whole-mount specimens of rat mesentery. Angiogenesis was studied in response to normal maturation, the injection of a mast cell degranulating substance (compound 48/80), and mild wounding. Confocal microscopy of specimens immunolabeled for elastin revealed a network of crosslinked elastic fibers with a density of 140.8 ± 37 mm of fiber/mm² tissue. Fiber diameters ranged from 180 to 1400 nm, with a mean value of 710 ± 330 nm. Capillary sprouts contained CD31- and OX-43-positive endothelial cells as well as desmin-positive pericytes. During normal maturation, leading endothelial cells and pericytes were in contact and aligned with an elastic fiber in ≃80–90% of all sprouts. In wounding and compound 48/80-treated …