Vascular permeability as a function of age was evaluated quantitatively and morphologically in skin of fetal Rhesus monkeys given vasoactive mediators. The response was examined at 90, 120 or 150 days of gestation or at birth and compared to the response of yearling Rhesus monkeys. Skin sites were challenged with histamine, compound 48/80 or bradykinin. Evans' blue and horseradish peroxidase were used as markers of vascular integrity. Evans' blue was quantified spectrophotometrically. Vascular permeability during fetal life was depressed. Fetal venules and capillaries had poorly formed basement membranes, an abundance of microfilaments within endothelial cells, occasional electron dense endothelial cells and infrequent deposits of extravascular peroxidase.
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