Avaliação dos efeitos cardiovasculares da Angiotensina-(1-9)

Abstract

Angiotensin-(1-9) is a nonapeptide formed by the hydrolysis of angiotensin I by ACE2 that seems to counter-regulate the classical RAS axis. Recent studies suggest that Ang-(1–9) acts via AT2 receptors (AT2R), however the pharmacological tool used to asses this Ang-(1-9) /AT2R mediated interaction, is the AT2R antagonist, PD123319, that appears to have a great deal of inespecificity . Two other candidates for the ligation of Ang-(1-9), that have protective effects similar to the AT2R are the MAS and the recently described MrgD receptor. Thus, in this study we addressed if Ang-(1-9) could be a ligand for AT2, MAS or MrgD receptors using aortic rings taken from AT2 and Mas knockout mice and AT2R or MrgD-transfected CHO cells. Materials and methods: The endothelium-dependent vasodilatory response to Ang-(1-9) was tested in aortic rings taken from Wild-Type, AT2KO and MASKO mice and Sprague-Dawley rats, pre-contracted with phenylephrine (0.1 umoles/L). NO release from AT2R or MrgD stable transfected CHO cells was evaluated using the NO indicator 4-amino-5 methylamino-2, 7 difluorofluoresceindiacetate (DAFFM) after Ang-(1-9) stimulation. Analyzed the in vivo cardiovascular parameters were recorded by a signal sent to a transducer connected to the cannula inserted into the abdominal aorta through the femoral artery, through data acquisition system (Biopac System, model MP150).Results: In aortic rings from SD rats Ang-(1-9) produced a dose-related relaxation which was not modified by A-779, the Mas/MrgD antagonist D-Pro7-Ang-(1-7); or by PD123319. In aortic rings taken from Mas KO there was a minor attenuation of the Ang-(1-9) vasorelaxant effect when compared to the WT. No difference between AT2KO and WT mice was observed regarding the vasorelaxation produced by Ang-(19). Moreover, the vasorelaxing effect of Ang-(1-9) was not affected by the association of PD123319 and D-Pro7-Ang-(1-7).In addition, the nonapeptide did not stimulate NO production in AT2R-stably transfected CHO cells or MrgD stably transfected cells. In vivo, we observed in SHR-SP rats cardiovascular effects of increasing doses of Ang-(1-9) within (20 min) injected into the carotid artery. But when injected into the femoral vein after 6hrs, we observed a significant decrease in mean arterial pressure. As attenuated the action of Ang II in the neurogenic model in mice.