Enhancement of Bradykinin and Resensitization of Its B ₂ Receptor

Abstract

Abstract-We studied the enhancement of the effects of bradykinin B 2 receptor agonists by agents that react with active centers of angiotensin-converting enzyme (ACE) independent of enzymatic inactivation. The potentiation and the desensitization and resensitization of B 2 receptor were assessed by measuring [ 3 H]arachidonic acid release and [Ca 2ϩ ] i mobilization in Chinese hamster ovary cells transfected to express human ACE and B 2 receptor, or in endothelial cells with constitutively expressed ACE and receptor. Administration of bradykinin or its ACE-resistant analogue desensitized the receptor, but it was resensitized (arachidonic acid release or [Ca 2ϩ T herapy with angiotensin I-converting enzyme (ACE) inhibitors initially was aimed at lowering elevated blood pressure. 1 By now, however, it has gained much wider applications in combating heart and kidney diseases, such as congestive heart failure and diabetic nephropathy, involving millions of patients. 2-7 Inhibitors of ACE affect both angiotensin II (Ang II) and bradykinin metabolism by blocking the production of the vasoconstrictor peptide and inactivating the vasodilator peptide, 8 but these actions alone do not completely explain, for example, the beneficial effects of ACE inhibitors on the heart. These effects are not only due to lowering systemic blood pressure and peripheral vascular resistance. In laboratory experiments, many of the improvements in cardiac function brought about by ACE inhibitors are blocked by the bradykinin B 2 receptor antagonist Hoe 140. 9 -14 We have observed, on the isolated atria 15 and ileum 16 of guinea pig, that ACE inhibitors potentiate the actions of bradykinin indirectly at the receptor level. Using cultured Chinese hamster ovary (CHO) cells cotransfected with the cDNA of human ACE and B 2 receptor, we showed that ACE inhibitors augment the release of signal transduction products by bradykinin independent of inhibiting the degradation of bradykinin but have no direct effect on the B 2 receptor. 17 On the basis of accumulated evidence, it was suggested that the above effects and the resensitization of the receptor, desensitized by an agonist, are due to a crosstalk between ACE and the B 2 receptor on the plasma membrane of the cells. We have also reported that angiotensin-(1-7), a substrate cleaved by the N-domain active site of ACE and an inhibitor of the C-domain active site in vitro, potentiates bradykinin at the receptor level in a manner similar to that of ACE inhibitors. 18 The present report extends and reconfirms the previous observations, mainly in different cells, by using ACE inhibitors, inhibitory and noninhibitory monoclonal and polyclonal antibodies, a mutated ACE molecule, and endogenous peptide and snake venom peptide substrates of ACE,8,19 to show

Angiotensin-Converting Enzyme Inhibition Increases Human Vascular Tissue-Type Plasminogen Activator Release Through Endogenous Bradykinin

“…ACE inhibitors potentiate the effects of BK not only by decreasing its degradation but also by enhancing sensitivity to BK at a receptor level. 27 In addition, BK may stimulate vasodilation and t-PA release through multiple or different mechanisms. For instance, administration of the NOS inhibitor L-NMMA attenuates the forearm vasodilator response to BK, indicating that the NO contributes to BK-induced vasodilation.…”

Angiotensin 1-9 and 1-7 Release in Human Heart

“…26 The release of Leu 10 of Ang I and the subsequent liberation of Ang II, assayed at pH 5.5, was decreased 53% to 67% by immunoprecipitation with antiserum to the truncated human rCATA. The release of Ang 1-7 was not reduced; its concentration actually increased in the supernatant (10% to 24%).…”

“…Cultured cells 7,26 in 6-well plates were loaded with 3 H-AA. The BK, ACE resistant BK analog (BKan), 7,28 and other agents were then added to cells.…”

“…23,24 CATA cleaves peptide bonds optimally at acid pH, but esters and amide bonds of C-terminal amino acids at a neutral pH. 19 It was reported that in micromolar concentration, Ang 1-9 inhibits ACE 25,26 and potentiates BK action on its B 2 receptor. 26 Here, we report that CATA is abundantly present in human heart tissues.…”

“…19 It was reported that in micromolar concentration, Ang 1-9 inhibits ACE 25,26 and potentiates BK action on its B 2 receptor. 26 Here, we report that CATA is abundantly present in human heart tissues. Its product of Ang I hydrolysis, Ang 1-9, and, at a somewhat higher concentration, Ang 1-7, enhances the effect of a kinin agonist on the B 2 receptor.…”