Mechanisms of T-kinin-induced increases in macromolecule extravasation in vivo

The purpose of this study was to investigate the mechanisms that mediate T-kinin- (Ile-Ser-bradykinin) induced increases in macromolecule extravasation in the hamster cheek pouch. Changes in plasma extravasation were quantified by counting the number of leaky sites and calculating the clearance of fluorescein isothiocyanate- (FITC) dextran (mol mass = 70 kDa) during suffusion of the cheek pouch with T-kinin (0.1-1.0 μM) by using intravital microscopy. T-kinin induced a significant time- and concentration- dependent increase in leaky site formation and clearance of FITC-dextran (P < 0.05). The increase in plasma extravasation in response to T-kinin was mediated by two mechanisms: a COOH-terminal-mediated stimulation of B₂ bradykinin receptors in postcapillary venules and an NH₂-terminal-mediated degranulation of mast cells leading to histamine release. Indomethacin and CP 96345, a selective nonpeptide neurokinin-1 receptor antagonist, had no significant effects on T-kinin-induced responses. We conclude that T-kinin increases macromolecule extravasation in the peripheral microcirculation by stimulating B₂ bradykinin receptors in post-capillary venules and by degranulating mast cells.