No abstract

Kaolin induced a clear and reproducible writhing reaction when intraperitoneally injected into mice. A simultaneous injection (i.p.) of soybean trypsin inhibitor (SBTI) significantly suppressed the kaolin-induced writhing reaction. This writhing reaction was markedly potentiated by a simultaneous injection (i.p.) of captopril. In an in vitro experiment kaolin caused kinin-release in mouse plasma, possibly through the activation of prekallikrein. This activation of plasma prekallikrein and kinin-release were inhibited in the presence of SBTI. Some non-steroidal anti-inflammatory agents inhibited the kaolin-induced writhing reaction dose-dependently. These results suggest that kaolin-induced writhing reaction may be caused by the released bradykinin through activation of the plasma kallikrein-kinin system. This model is a novel and simple tool for assessment of analgesic agents.

No abstract

Abstract-Using a bradykinin enzyme immunoassay, we measured the amount of kinin in the peritoneal washings of mice with the kaolin-induced writhing reaction. Simultaneous treatment with captopril, a kininase II inhibitor, significantly increased the kinin level at 1 min after kaolin injection.Soybean trypsin inhibitor injected simultaneously with kaolin almost completely suppressed the kinin level at 1 min with or without treatment of captopril.These results suggest that kinin is released through activation of the plasma kallikrein-kinin system by kaolin, and that kinin could be a main mediator for the writhing reaction.

To develop a specific antagonist of platelet ␣IIb␤3 using small linear peptides, we synthesized a series of hexapeptides that did not have an Arg-Gly-Asp (RGD) sequence and examined their anti-platelet activity and their specificity for ␣IIb␤3. We found a novel motif sequence, Pro-X1-X2-X3-Asp-X4, where X1 to X4 were all L-form ␣-amino acids, which specifically inhibited aggregation of human platelets at submicromolar concentrations. The Pro residue at the N terminus was essential to the anti-platelet activity, and the acetylation of the imino group of this residue also resulted in the complete loss of the activity. The results of the binding assay using purified human platelet ␣IIb␤3 and placental ␣v␤3 and those of the cell adhesion assay suggest that this motif peptide is highly specific for platelet ␣IIb␤3 among other integrins. Flow cytometric studies using an fluorescein isothiocyanate-labeled RGD peptide showed that this motif peptide inhibited the binding of an RGD peptide to activated platelets, suggesting that it has the same inhibitory mode as RGD peptides. Conformational analysis of this motif peptide and an RGD-containing peptide suggests that the imino group of the Pro residue may substitute for the role of the guanidino group of the Arg residue of the RGD sequence.Integrins are heterodimeric cell surface receptor molecules and are thought to be particularly important mediators of cell adhesion, cell migration, and adhesion-dependent intracellular signaling. Until now, more than 20 integrin receptors have been identified, and many of them recognize the Arg-Gly-Asp (RGD) 1 sequence as a common recognition motif within their putative ligands upon ligand-receptor interaction (1-4). The ligand binding specificity has been studied by many investigators, and it has been revealed that some integrins show apparent redundancy in integrin-ligand interactions. For example, ␣v␤3, a so-called vitronectin receptor, can bind several apparently dissimilar ligands such as vitronectin, fibrinogen, fibronectin, von Willebrand factor, osteopontin, and bone sialoprotein, all of which have the RGD sequence (reviewed in Refs. 5 and 6). In addition, the same RGD site within a ligand can be recognized by several different integrins. These apparent redundancies in integrin-ligand interactions are very interesting aspects of integrin receptors and may be beneficial to the cell adhesion of many types of cells to extracellular matrix proteins.We are interested in developing small peptides that are specific for each integrin as a tool for investigating ligandintegrin interactions and as an agent for therapeutic uses. Recently, many small peptides containing the RGD sequence have been synthesized, and their specificity toward integrins has been examined (7,8). Most of the linear RGD peptides have shown very low specificity among many types of integrin receptors including platelet ␣IIb␤3 (fibrinogen receptor), ␣v␤3 (vitronectin receptor), and ␣5␤1 (fibronectin receptor). In the case of ␣IIb␤3 and ␣v␤3, both integrins have the same...