Potentiation of the Vascular Response to Kinins by Inhibition of Myocardial Kininases

Abstract

Abstract-Inhibitors of angiotensin I-converting enzyme (ACE) are very efficacious in the potentiation of the actions of bradykinin (BK) and are able to provoke a B 2 receptor-mediated vasodilation even after desensitization of this receptor. Because this activity cannot be easily explained only by an inhibition of kinin degradation, direct interactions of ACE inhibitors with the B 2 receptor or its signal transduction have been hypothesized. To clarify the significance of degradation-independent potentiation, we studied the vasodilatory effects of BK and 2 degradation-resistant B 2 receptor agonists in the isolated rat heart, a model in which ACE and aminopeptidase P (APP) contribute equally to the degradation of BK. Coronary vasodilation to BK and to a peptidic (B6014) and a nonpeptidic (FR190997) degradation-resistant B 2 agonist was assessed in the presence or absence of the ACE inhibitor ramiprilat, the APP inhibitor mercaptoethanol, or both. Ramiprilat or mercaptoethanol induced leftward shifts in the BK dose-response curve (EC 50 ϭ3.4 nmol/L) by a factor of 4.6 or 4.9, respectively. Combined inhibition of ACE and APP reduced the EC 50 of BK to 0.18 nmol/L (ie, by a factor of 19) but potentiated the activity of B6014 (EC 50 ϭ1.9 nmol/L) only weakly without altering that of FR190997 (EC 50 ϭ0.34 nmol/L). Desensitization of B 2 receptors was induced by the administration of BK (0.2 mol/L) or FR190997 (0.1 mol/L) for 30 minutes; the vascular reactivity to ramiprilat or increasing doses of BK was tested thereafter. After desensitization with BK, but not FR190997, an additional application of ramiprilat provoked a B 2 receptor-mediated vasodilation. High BK concentrations were still effective at the desensitized receptor. The process of desensitization was not altered by ramiprilat. These results show that in this model, all potentiating actions of ACE inhibitors on kinin-induced vasodilation are exclusively related to the reduction in BK breakdown and are equivalently provoked by APP inhibition. The desensitization of B 2 receptors is overcome by increasing BK concentrations, either directly or through the inhibition of ACE. These observations do not suggest any direct interactions of ACE inhibitors with the B 2 receptor or its signal transduction but point to a very high activity of BK degradation in the vicinity of the B 2 receptor in combination with a stimulation-dependent reduction in receptor affinity. (Hypertension. 2000;35:32-37.)Key Words: bradykinin Ⅲ angiotensin-converting enzyme Ⅲ receptor, bradykinin Ⅲ rats Ⅲ heart I nhibitors of angiotensin I-converting enzyme (ACE) have been proved to be clinically effective against diseases such as hypertension, congestive heart failure, and myocardial infarction. Through their main mechanism of action (ie, inhibition of the peptidase ACE), ACE inhibitors not only prevent the activation of angiotensin I but also eliminate a degradation pathway for the vasodilatory peptide bradykinin (BK) and thus increase the availability and effectiveness of kinins. The results...

Endopeptidases 3.4.24.15 and 24.16 in endothelial cells: potential role in vasoactive peptide metabolism

“…The effects of the EP24.15 and EP24.16 inhibitors on QFS-cleaving activity in cytosolic and solubilized membrane fractions of EA.hy926 cells are shown in Fig. 2 [6][7][8][9] , although BK [1][2][3][4][5][6][7] and BK [8][9] were sometimes also observed, particularly in EA.hy926 extracts (Fig. 3A).…”

“…3A). Because BK [1][2][3][4][5][6][7] partially coeluted with the BK 1-5 peak, making quantitation of the latter difficult, phosphoramidon (50 M) was added to inhibit its generation by NEP-like enzymes. In the presence of phosphoramidon, the formation of BK [1][2][3][4][5] and BK 6-9 by EA.hy926 cytosol was inhibited 60-70% by cFP and JA2, and to a lesser extent (20- Fig.…”

“…BK degradation was significantly reduced in the presence of 50 M phosphoramidon (rate reduced to 110 nmol ⅐ mg protein Ϫ1 ⅐ h Ϫ1 ), leaving primarily BK 1-5 and BK 6-9 fragments, as well as BK [1][2][3][4][5][6][7] and BK [8][9] (Fig. 3B).…”

“…peptidase; bradykinin; inhibitor; endothelium THE VASODILATORY PEPTIDE bradykinin (BK) is readily degraded in the circulation by a number of metallopeptidases, including angiotensin-converting enzyme (ACE), neutral endopeptidase (NEP), aminopeptidase P, carboxypeptidases, and possibly endothelin-converting enzyme-1 (ECE-1) (12, 25). Recent evidence suggests that a portion of the hypotensive and particularly the cardioprotective effects of specific inhibitors of ACE and NEP are due to enhanced BK activity (5,17,22,23). BK is also efficiently cleaved in vitro by the closely related peptidases EP24.15 (also known as thimet oligopeptidase) and EP24.16 (also known as neurolysin) (21).…”

“…Recent evidence suggests that a portion of the hypotensive and particularly the cardioprotective effects of specific inhibitors of ACE and NEP are due to enhanced BK activity (5,17,22,23). BK is also efficiently cleaved in vitro by the closely related peptidases EP24.15 (also known as thimet oligopeptidase) and EP24.16 (also known as neurolysin) (21).…”