Stimulation of Cyclic GMP Production via AT 2 and B 2 Receptors in the Pressure-Overloaded Aorta After Banding

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Abstract
Abdominal aortic banding induces upregulation of the angiotensin II (Ang II) type-2 (AT 2 ) receptor, thereby decreasing the contractile response to Ang II in the thoracic aorta of the rat. The aim of this study was to use a mouse model to clarify the mechanisms by which the banding elicits upregulation of the aortic AT 2 receptor and the subsequent attenuation of Ang II responsiveness. Concomitantly with the elevation in blood pressure and plasma renin concentration after banding, AT 2 -receptor mRNA levels in the thoracic aorta rapidly increased in mice within 4 days. Upregulation of the AT 2 receptor, as well as blood pressure elevation after banding, was abolished by losartan administration. The contractile response to Ang II was depressed in aortic rings of banding mice but not of sham mice, and was restored by either the AT 2 -receptor antagonist PD123319 or the bradykinin B 2 -receptor antagonist icatibant. cGMP content in the thoracic aorta of banding mice was 9-fold greater than that of sham mice, and the elevation was reduced to sham levels 1 hour after intravenous injection of PD123319 or icatibant. When aortic rings were incubated with Ang II, cGMP content increased in banding rings but not in sham rings; the pretreatment with PD123319 or icatibant inhibited Ang II-induced cGMP production. These results suggest that aortic banding induces upregulation of the AT 2 receptor through increased circulating Ang II via the AT 1 receptor, thereby activating a vasodilatory pathway in vessels through the AT 2 receptor via the kinin/cGMP system.

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