SUMMARY 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 mediumsized 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.
The tissue kallikrein-kinin system contributes to the regulation of local blood flow, vascular permeability, inflammatory responses, and ion transport. Tissue kallikrein is a serine proteinase which produces vasoactive kinin peptides. Kallistatin specifically binds to tissue kallikrein and inhibits its proteolytic activity. To investigate their anatomical relationship in the human pancreas and salivary glands, the expression and localization of kallistatin and tissue kallikrein were identified by immunoassays, immunohistochemistry, and in situ hybridization histochemistry. Human kallistatin and tissue kallikrein levels were measured by ELISA and radioimmunoassay, respectively, in pancreatic and salivary tissue extracts, and in pancreatic fluid and saliva. Immunoreactive kallistatin and kallikrein were colocalized in acinar cells of the human pancreas by immunohistochemistry. In situ hybridization histochemistry confirmed the presence of both mRNAs in pancreatic acini. In salivary glands, kallistatin and kallikrein mRNAs were also colocalized in serous acinar cells, and the kallikrein transcript was further localized to striated and interlobular ducts. Immunoreactive kallistatin was localized in serous acinar and demilune cells of salivary glands and kallikrein was localized to the epithelium of striated and interlobular ducts. The colocalization and/or coexpression of human tissue kallikrein and kallistatin in the pancreas and salivary glands suggest a role for kallistatin in the regulation of tissue kallikrein in these organs.
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