Dimensions of Postcapillary Venules Sensitive to Bradykinin and Histamine-induced Leakage of Macromolecules

Abstract

Microvascular leakage of macromolecules was studied in the hamster cheek pouch preparation using fluorescein labelled dextran (FITC-dextran 145 M_w = 145,000) as a tracer. When the preparation is superfused with 10⁻⁵ M histamine or 10⁻⁷ M bradykinin the permeability to macromolecules increases exclusively at postcapillary venules. Microinjections of 30–200 picolitres (pl) of 0.1 M histamine and 10⁻⁴ M bradykinin close to arterioles and capillaries caused extravasation from several postcapillary venules at a distance from site of injection but not from arterioles or capillaries. The minimal diameter of the postcapillary venules where leakage occurred was (n = 45) 8.6 ± 2.6 (S.D.) μm and the maximal diameter was 14.0 ± 5.3 μm. Histamine and bradykinin caused leakage of macromolecules in postcapillary venules but not in arterioles, capillaries or larger venules even when these were exposed to high local concentrations of these agents.