BACKGROUND - Bradykinin stimulates dose-dependent tissue plasminogen activator (tPA) release from human endothelium. Although bradykinin is known to cause vasodilation through B(2) receptor-dependent effects on NO, prostacyclin, and endothelium-derived hyperpolarizing factor production, the mechanism(s) underlying tPA release is unknown.
METHODS AND RESULTS - We measured the effects of intra-arterial bradykinin (100, 200, and 400 ng/min), acetylcholine (15, 30, and 60 microg/min), and nitroprusside (0.8, 1.6, and 3.2 microg/min) on forearm vasodilation and tPA release in healthy volunteers in the presence and absence of (1) the B(2) receptor antagonist HOE 140 (100 microg/kg IV), (2) the NO synthase inhibitor L-N:(G)-monomethyl-L-arginine (L-NMMA, 4 micromol/min intra-arterially), and (3) the cyclooxygenase inhibitor indomethacin (50 mg PO TID). B(2) receptor antagonism attenuated vasodilator (P:=0.004) and tPA (P:=0.043) responses to bradykinin, without attenuating the vasodilator response to nitroprusside (P:=0.36). L-NMMA decreased basal forearm blood flow (from 2.35+/-0.31 to 1. 73+/-0.22 mL/min per 100 mL, P:=0.01) and blunted the vasodilator response to acetylcholine (P:=0.013) and bradykinin (P:=0.07, P:=0. 038 for forearm vascular resistance) but not that to nitroprusside (P:=0.47). However, there was no effect of L-NMMA on basal (P:=0.7) or bradykinin-stimulated tPA release (P:=0.45). Indomethacin decreased urinary excretion of the prostacyclin metabolite 2, 3-dinor-6-keto-prostaglandin F(1alpha) (P:=0.04). The vasodilator response to endothelium-dependent (P:=0.019 for bradykinin) and endothelium-independent (P:=0.019) vasodilators was enhanced during indomethacin administration. In contrast, there was no effect of indomethacin alone (P:=0.99) or indomethacin plus L-NMMA (P:=0.36) on bradykinin-stimulated tPA release.
CONCLUSIONS - These data indicate that bradykinin stimulates tPA release from human endothelium through a B(2) receptor-dependent, NO synthase-independent, and cyclooxygenase-independent pathway. Bradykinin-stimulated tPA release may represent a marker for the endothelial effects of endothelium-derived hyperpolarizing factor.