EFFECT OF DES ARGININE-9-BRADYKININ AND OTHER BRADYKININ FRAGMENTS ON THE SYNTHESIS OF PROSTACYCLIN AND THE BINDING OF BRADYKININ BY VASCULAR CELLS IN CULTURE

Bradykinin (BK) fragments, des arg1-BK, des arg1,pro2-BK, des phe8,arg9-BK and des pro7,phe8,arg9-BK were synthesized and along with des arginine9-BK (daBK), tested for their ability to induce prostacyclin synthesis in homogeneous cultures of cells from the calf pulmonary artery. Of the fragments daBK was the only peptide, in addition to bradykinin (BK), to activate the synthesis of prostacyclin (PGI2) and platelet activating factor (PAF) in endothelial cells and PGI2 in fibroblasts and smooth muscle cells. Half-maximal activation of PGI2 synthesis differed with the cell type. The other fragments tested did not directly affect PGI2 synthesis. These fragments also did not inhibit daBK or BK activation of PG synthesis. BK bound to endothelial cells with a dissociation constant (Kd) of 2.1 nM and a Bmax of 47.9 fmoles/106 cells. The Kd for the binding of BK to smooth muscle cells and fibroblasts was somewhat higher, 4.9 nM and 7.9 nM, respectively. None of the fragments tested, including daBK, altered the binding of BK. Des arg9[leu]-BK, reported to be a competitive antagonist of the bradykinin B1 receptor, inhibited daBK induced PG of PAF synthesis in endothelial cells but had little effect of BK binding or BK induced PG synthesis. Finally, the BK antagonist [thi5,8, d-phe7]-BK blocked both BK binding and the ability of either BK or daBK to induce PG synthesis, thus substantiating that the binding of these kinins is a step in the activation of PG synthesis.