Angiotensin II type 2 receptor overexpression activates the vascular kinin system and causes vasodilation
Yoshiaki Tsutsumi, … , Hakuo Takahashi, Toshiji Iwasaka
Yoshiaki Tsutsumi, … , Hakuo Takahashi, Toshiji Iwasaka
Published October 1, 1999
Citation Information: J Clin Invest. 1999;104(7):925-935. https://doi.org/10.1172/JCI7886.
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Article

Angiotensin II type 2 receptor overexpression activates the vascular kinin system and causes vasodilation

Abstract

Angiotensin II (Ang II) is a potent vasopressor peptide that interacts with 2 major receptor isoforms — AT1 and AT2. Although blood pressure is increased in AT2 knockout mice, the underlying mechanisms remain undefined because of the low levels of expression of AT2 in the vasculature. Here we overexpressed AT2 in vascular smooth muscle (VSM) cells in transgenic (TG) mice. Aortic AT1 was not affected by overexpression of AT2. Chronic infusion of Ang II into AT2-TG mice completely abolished the AT1-mediated pressor effect, which was blocked by inhibitors of bradykinin type 2 receptor (icatibant) and nitric oxide (NO) synthase (L-NAME). Aortic explants from TG mice showed greatly increased cGMP production and diminished Ang II–induced vascular constriction. Removal of endothelium or treatment with icatibant and L-NAME abolished these AT2-mediated effects. AT2 blocked the amiloride-sensitive Na+/H+ exchanger, promoting intracellular acidosis in VSM cells and activating kininogenases. The resulting enhancement of aortic kinin formation in TG mice was not affected by removal of endothelium. Our results suggest that AT2 in aortic VSM cells stimulates the production of bradykinin, which stimulates the NO/cGMP system in a paracrine manner to promote vasodilation. Selective stimulation of AT2 in the presence of AT1 antagonists is predicted to have a beneficial clinical effect in controlling blood pressure.

Authors

Yoshiaki Tsutsumi, Hiroaki Matsubara, Hiroya Masaki, Hiroki Kurihara, Satoshi Murasawa, Shinji Takai, Mizuo Miyazaki, Yoshihisa Nozawa, Ryoji Ozono, Keigo Nakagawa, Takeshi Miwa, Noritaka Kawada, Yasukiyo Mori, Yasunobu Shibasaki, Yohko Tanaka, Soichiro Fujiyama, Yohko Koyama, Atsuko Fujiyama, Hakuo Takahashi, Toshiji Iwasaka

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AT2-mediated intracellular acidosis through inhibition of the amiloride-...
AT2-mediated intracellular acidosis through inhibition of the amiloride-sensitive Na+/H+ exchanger. The pH-sensitive dye BCECF was used to monitor changes in cytosolic pHi as described in Methods. The aortic VSM cells from wild-type (a) and AT2-TG (b) mice were rinsed and loaded with 2 μmol/L BCECF for 60 minutes at 37°C. Fluorescence was monitored at 530 nm, with excitation wavelengths of 450 and 500 nm in the ratio mode. After measurement of the basal pHi level, the control medium was changed to that with varying extracellular pH. The fluorescence signal was calibrated at several pH values (6.6, 7.0, and 7.4) in KCl solution containing the K+/H+ ionophore nigericin. CV11974 (CV; 0.5 μmol/L), PD123319 (PD; 0.5 μmol/L), and DMA (30 μmol/L) were preadded; then the cells were exposed to Ang II (100 nmol/L). Similar results were obtained from 6 separate experiments, and representative data are shown (top panels). Changes of pHi from the baseline values 10 minutes after addition of Ang II were calculated, and are shown relative to the baseline value (bottom panels; n = 6). *P < 0.05, **P < 0.01 vs. the baseline value.