Angiotensin II type 2 receptor overexpression activates the vascular kinin system and causes vasodilation
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
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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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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Ang II–induced constrictive response of the aorta (a and b), expression ...
Ang II–induced constrictive response of the aorta (a and b), expression profile of vascular constriction–related proteins (c), and electron micrography of the aorta of AT2-TG mice (d). (a and b) Aortic strips were placed on a myograph under resting tension and equilibrated in bathing medium continuously bubbled with O2/CO2 (95:5). The contractile response to 50 mmol/L Ang II was examined 3 times, and the contractile response after the third Ang II treatment was regarded as the control response for Ang II (100%). Subsequently, the medium was washed out twice with fresh Tyrode’s solution, and the vascular response to Ang II (50 nmol/L; n = 8) was recorded in the presence or absence of PD123319 (100 nmol/L; n = 8), L-NAME (1 μmol/L; n = 8), or icatibant (100 nmol/L; n = 8). Removal of endothelium was performed by gently rubbing the intimal surface with a cotton pellet, and was verified by abolishment of the relaxation caused by 1 μmol/L acetylcholine. The results are expressed as means ± SE. *P < 0.001 vs. the control level. (c) Aortic homogenates (20 μg protein) were analyzed by Western blotting using anti-caldesmon (high molecular weight), anti–α-actin, and anti-calponin antibodies. Representative data of 3 separate experiments are shown. (d) Electron micrograph of a longitudinal section of smooth muscle fibers (VSM cells) in the aorta from AT2-TG mice. Part of the centrally located nucleus (N) is included at the right. Mitochondria (M), a Golgi apparatus (G), and ribosomes (R) are particularly abundant in the conical perinuclear region. Caveolae (C) are seen in plasma membranous regions. The remainder of the fiber is occupied by thin filaments (myofilament) (asterisk) and by dense bodies (arrows), into which the filaments appear to insert.