Potentiation of bradykinin-induced tissue plasminogen activator release by angiotensin-converting enzyme inhibition

OBJECTIVES The aim of the present study was to determine the effect of angiotensin-converting enzyme (ACE) inhibition on the local stimulated release of tissue plasminogen activator (t-PA) from the endothelium. BACKGROUND Angiotensin-converting enzyme inhibitor therapy may exert a beneficial effect on the endogenous fibrinolytic balance. METHODS Blood flow and plasma fibrinolytic factors were measured in both forearms of eight healthy males who received unilateral brachial artery infusions of the endothelium-dependent vasodilators substance P (2 to 8 pmol/min) and bradykinin (100 to 1,000 pmol/min), and the endothelium-independent vasodilator sodium nitroprusside (2 to 8 μg/min). These measurements were performed on each of three occasions following one week of matched placebo, quinapril 40 mg or losartan 50 mg daily administered in a double-blind randomized crossover design. RESULTS Sodium nitroprusside, substance P and bradykinin produced dose-dependent increases in the blood flow of infused forearm (analysis of variance [ANOVA], p < 0.001 for all). Although sodium nitroprusside did not affect plasma t-PA concentrations, they were increased dose-dependently in the infused forearm by substance P and bradykinin infusion (ANOVA, p < 0.001 for both). Bradykinin-induced release of active t-PA was more than doubled during treatment with quinapril in comparison to placebo or losartan (two-way ANOVA: p < 0.003 for treatment group, p < 0.001 for t-PA response and P = ns for interaction), whereas the substance P response was unaffected. CONCLUSIONS We have shown a selective and marked augmentation of bradykinin-induced t-PA release during ACE inhibition. These findings suggest that the beneficial clinical and vascular effects of ACE inhibition may, in part, be mediated through local augmentation of bradykinin-induced t-PA release.