High intraluminal pressure via H2O2 upregulates arteriolar constrictions to angiotensin II by increasing the functional availability of AT1 receptors

Abstract

Previously, we found that high intraluminal pressure leads to production of reactive oxygen species (ROS) and also upregulates several components of the renin-angiotensin system in the wall of small arteries. We hypothesized that acute exposure of arterioles to high intraluminal pressure in vitro via increasing ROS production enhances the functional availability of type 1 angiotensin II (Ang II) receptors (AT1 receptors), resulting in sustained constrictions. In arterioles ( approximately 180 mum) isolated from rat skeletal muscle, Ang II elicited dose-dependent constrictions, which decreased significantly by the second application [maximum (max.): from 59% +/- 4% to 26% +/- 5% at 10(-8) M; P < 0.05] in the presence of 80 mmHg of intraluminal pressure. In contrast, if the arterioles were exposed to high intraluminal pressure (160 mmHg for 30 min), Ang II-induced constrictions remained substantial on the second application (max.: 51% +/- 3% at 10(-8) M). In the presence of Tiron and polyethylene glycol (PEG)-catalase, known to reduce the level of superoxide anion and hydrogen peroxide (H(2)O(2)), second applications of Ang II evoked similarly reduced constrictions, even after high-pressure exposure (29% +/- 4% at 10(-8) M). Furthermore, when arterioles were exposed to H(2)O(2) (for 30 min, 10(-7) M, at normal 80 mmHg pressure), Ang II-induced constrictions remained substantial on second applications (59% +/- 5% at 10(-8) M). These findings suggest that high pressure, likely via inducing H(2)O(2) production, increases the functional availability of AT1 receptors and thus enhances Ang II-induced arteriolar constrictions. We propose that in hypertension-regardless of etiology-high intraluminal pressure, via oxidative stress, enhances the functional availability of AT1 receptors augmenting Ang II-induced constrictions.

Fig. 1.

Original records (A) and summary data (n = 11; B) of constrictions of arterioles to repeated applications (appl.) of angiotensin II (Ang II; 0.1 nmol/l to 0.1 μmol/l) in the presence of 80 mmHg and after exposure of 160 mmHg intraluminal pressure (n = 10; C). WO, washout. Data are means ± SE. *P < 0.05.

Fig. 2.

Constrictions of arterioles to repeated applications of Ang II (0.1 nmol/l to 0.1 μmol/l) in the presence of the Ang II type 2 (AT2) receptor antagonist, PD-123319, at 80 mmHg and after exposure of 160 mmHg pressure (n = 7; A). Constrictions of arterioles to repeated applications of norepinephrine (0.1 μmol/l) in the absence (n = 7; B) and presence (n = 7; C) of the AT2 receptor antagonist, PD-123319, at 80 mmHg and after exposure of 160 mmHg pressure. Data are means ± SE. *P < 0.05.

Fig. 3.

Original records (A) and summary data (n = 7; B) of constrictions of arterioles to repeated applications of Ang II (0.1 nmol/l to 0.1 μmol/l) exposed to 160 mmHg intraluminal pressure in the presence of reactive oxygen species scavenger Tiron and polyethylene glycol (PEG)-catalase (PEG-Cat). Data are means ± SE. *P < 0.05.

Fig. 4.

Original records (A) and summary data (n = 7; B) of constrictions of arterioles to repeated applications of Ang II (0.1 nmol/l to 0.1 μmol/l) exposed to H₂O₂ (0.1 μM for 30 min) in the presence of 80 mmHg intraluminal pressure. Data are means ± SE.