Kallikrein-binding Protein and Vasodilation

Kallistatin is a serine proteinase inhibitor which binds to tissue kallikrein and inhibits its activity. The aim of this study is to evaluate if kallistatin has a direct effect on the vasculature and on blood pressure homeostasis. We found that an intravenous bolus injection of human kallistatin caused a rapid, potent, and transient reduction of mean arterial blood pressure in anesthetized rats. Infusion of purified kallistatin (0.07–1.42 nmol/kg) into cannulated rat jugular vein produced a 20–85 mmHg reduction of blood pressure in a dose-dependent manner. Hoe 140, a bradykinin B 2 -receptor antagonist, had no effect on the hypotensive effect of kallistatin yet it abolished the blood pressure–lowering effect of kinin and kallikrein. Relaxation of isolated aortic rings by kallistatin was observed in the presence (ED 50 of 3.4 3 10 2 9 M) and in the absence of endothelium (ED 50 of 10 2 9 M). Rat kallikrein-binding protein, but not kinin or kallikrein, induced vascular relaxation of aortic rings. Neither Hoe 140 nor N v -nitroL -arginine methyl ester, a nitric oxide synthase inhibitor, affected vasorelaxation induced by kallistatin. Kallistatin also caused dose-dependent vasodilation of the renal vasculature in the isolated, perfused rat kidney. Specific kallistatin-binding sites were identified in rat aorta by Scatchard plot analysis with a K d of 0.25 6 0.07 nM and maximal binding capacity of 47.9 6 10.4 fmol/mg protein (mean 6 SEM, n 5 3). These results indicate that kallistatin is a potent vasodilator which may function directly through a vascular smooth muscle mechanism independent of an endothelial bradykinin receptor. This study introduces the potential significance of kallistatin in directly regulating blood pressure to reduce hypertension. ( J. Clin. Invest . 1997. 100: 11–17.)