Dimensions of postcapillary venules sensitive to bradykinin and histamine-induced leakage of macromolecules

Microvascular leakage of macromolecules was studied in the hamster cheek pouch preparation using fluorescein labelled dextran (FITC-dextran 145 Mw = 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.) microM and the maximal diameter was 14.0 +/- 5.3 microM. 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.