Localization and expression of tissue kallikrein and kallistatin in human blood vessels.

Tissue kallikrein releases kinins by specific proteolysis, an activity inhibited by kallistatin. In this study, kallikrein and kallistatin were localized to endothelial and smooth muscle cells of large, medium, and small normal blood vessels by immunohistochemical techniques. Immunostaining for both proteins was strong in the endothelium of all sizes of blood vessels and was more intense in medial smooth muscle cells of small and medium-sized blood vessels than in elastic arteries. The sites of synthesis by endothelial and smooth muscle cells were demonstrated in normal blood vessels of all sizes by in situ hybridization histochemistry. Kallikrein and kallistatin levels were measured by immunoassays in homogenates of human aorta, vena cava, and iliac artery and vein. Tissue kallikrein and kallistatin transcripts were identified in human blood vessels by RT-PCR followed by Southern blot analysis with specific oligonucleotide probes. The results demonstrated the expression and co-localization of tissue kallikrein and kallistatin in human vessels and suggest a potential role of kallistatin in regulating tissue kallikrein in blood vessels.