Potentiation of the hypotensive effect of bradykinin by angiotensin-(1–7)-related peptides Renata D. Paula, Celso V. Lima, Raquel R. Britto, Maria J. Campagnole–Santos, Mahesh C. Khosla 1 , Robson A.S. Santos* Laborato ´rio de Hipertensa ˜o, Departamento de Fisiologia e Biofı ´sica Instituto de Cie ˆncias Biolo ´gicas, Universidade Federal de Minas Gerais 31 270 –901, Belo Horizonte, MG, Brazil Received 16 September 1998; accepted 18 November 1998 Abstract In this study, we evaluated the bradykinin potentiating activity and ACE inhibitory activity of several Ang-(1–7)-related peptides: Ang-(2–7), Ang-(3–7), Ang-(4 –7), Ang-(1– 6), Ang-(1–5) and the selective antagonist of Ang-(1–7): D-[Ala 7 ]Ang-(1–7) (A-779). In vivo experiments were performed in freely moving Wistar rats. ACE activity was evaluated by a fluorometric assay in rat plasma using Hip-His-Leu as a substrate. Intravenous injections of Ang-(1–7) (2.2 nmol) transformed the effect of a single dose of bradykinin (1 nmol) into the effect produced by a double dose. A similar bradykinin potentiating activity was demonstrated for Ang-(2–7) and Ang-(3–7). On the other hand, Ang-(1–5), Ang-(1– 6), Ang-(4 –7) and A-779 did not change the hypotensive effect of bradykinin in doses ranging from 8 up to 25 nmols. The hypotensive effect of bradykinin was increased by intravenous infusion (0.3 ng/min) of Ang-(1–7)  Ang-(2–7)  Ang-(3–7). Conversely, Ang-(1–5), Ang-(1– 6), Ang-(4 –7) or A-779 did not change the hypotensive effect of bradykinin. ACE inhibition with Ang-(1–7) related peptides occurred in the order: Ang-(2–7)  Ang-(3–7)  Ang-(1–7) [] Ang-(1–5)  Ang-(4 –7)  Ang-(1– 6)  A-779. A-779 in concentrations up to 10 -5 M did not change the ACE inhibitory activity of Ang-(1–7). These results suggest that Ang-(1–7), Ang-(2–7) and Ang-(3–7) can modulate bradykinin actions in vivo. More important, our data pointed out that alternative mechanisms besides interaction with ACE are required to explain the bradykinin potentiating activity of Ang-(1–7). © 1999 Elsevier Science Inc. All rights reserved. Keywords: Kinins; Angiotensins; Blood vessels; Converting enzyme inhibitors; Endothelial cells; Angiotensin-(1–7); Angiotensin-(1– 6); Angiotensin-(1–5); Angiotensin-(2–7); Angiotensin-(3–7); Angiotensin-(4 –7); A-779 1. Introduction The heptapeptide angiotensin (Ang)-(1–7) differs impor- tantly from Ang II by being formed in an independent enzymatic cascade [13,37] and by possessing selective an- giotensinergic actions that can even be the opposite of Ang II [6,15]. Ang-(1–7) can be formed directly from Ang I by a non-ACE pathway [34] and is essentially devoid of the most classic Ang II actions: induction of drinking and va- soconstriction [13,23,37]. On the other hand, Ang-(1–7) can improve the baroreceptor reflex [6] and decrease smooth muscle growth [15], actions that are opposite to those ob- served with Ang II. We have previously described that Ang-(1–7) potentiates bradykinin (BK) in freely moving rats [25,31]. These find- ings have been confirmed in vitro [5,10,18,24]. The poten- tiation of BK in vivo was dose-dependent, independent of ACE blockade, and appeared to involve the release of pros- taglandins [31] and nitric oxide [32]. Additionally, because the Ang-(1–7) antagonist [D-Ala 7 ]-Ang-(1–7) (A-779) com- pletely abolished BK potentiation by Ang-(1–7) [25], the possibility that this interaction is a receptor-mediated event must be considered. Although a similar action was also observed in vivo for Ang II and Ang I [33], the possibility that these peptides could be converted to Ang-(1–7) [37] and the fact that the heptapeptide is essentially devoid of vasoconstrictor action makes this effect particularly impor- tant, especially considering that Ang-(1–7) can increase in plasma after chronic blockade of AT 1 receptors [12] or ACE inhibition [7]. In these situations, the Ang-(1–7)/BK inter- * Corresponding author. Tel./fax: +55-31-499-2924/499-2956. E-mail address: marrob@dedalus.lcc.ufmg.br (R.A.S. Santos) 1 MCK is from the Cleveland Clinic Foundation, OH, USA. Peptides 20 (1999) 493–500 0196-9781/99/$ – see front matter © 1999 Elsevier Science Inc. All rights reserved. PII: S0196-9781(99)00031-5