Adenoviral inhibition of AT_1a receptors in the paraventricular nucleus inhibits acute increases in mean arterial blood pressure in the rat

Abstract

Brain and peripheral renin-angiotensin systems are important in blood pressure maintenance. Circulating ANG II stimulates brain RAS to contribute to the increase mean arterial pressure (MAP). This mechanism has not been fully clarified, so it was hypothesized that reducing angiotensin type 1a (AT 1a) receptors (AT1aRs) in the paraventricular nucleus (PVN) would diminish intravenous ANG II-induced increases in MAP. Adenoviruses (Ad) encoding AT 1a small hairpin RNA (shRNA) or Ad-LacZ (marker gene) were injected into the PVN [1 ϫ 10 9 plaque-forming units/ml, bilateral (200 nl/site)] of male SpragueDawley rats instrumented with radiotelemetry transmitters for MAP and heart rate measurements and with venous catheters for drug administration. No differences in weight gain or basal MAP were observed. ANG II (30 ng · kg Ϫ1 · min Ϫ1 iv, 15 l/min for 60 min) was administered 3, 7, 10, and 14 days after PVN Ad injection to increase blood pressure. ANG II-induced elevations in MAP were significantly reduced in PVN Ad-AT 1a shRNA rats compared with Ad-LacZ rats (32 Ϯ 6 vs. 8 Ϯ 9 mmHg at 7 days, 35 Ϯ 6 vs. 10 Ϯ 6 mmHg at 10 days, and 32 Ϯ 2 vs. 1 Ϯ 5 mmHg at 14 days; P Ͻ 0.05). These observations were confirmed by acute administration of losartan (20 nmol/l, 100 nl/site) in the PVN prior to short-term infusion of ANG II; the ANG II-pressor response was attenuated by 69%. In contrast, PVN Ad-AT 1a shRNA treatment did not influence phenylephrine-induced increases in blood pressure (30 g·kg Ϫ1 · min Ϫ1 iv, 15 l/min for 30 min). Importantly, PVN Ad-AT 1a shRNA did not alter superior mesenteric arterial contractility to ANG II or norepinephrine; AChinduced arterial relaxation was also unaltered. ␤-Galactosidase staining revealed PVN Ad transduction, and Western blot analyses revealed significant reductions of PVN AT 1 protein. In conclusion, PVN-localized AT1Rs are critical for short-term circulating ANG II-mediated elevations of blood pressure. A sustained suppression of AT1aR expression by single administration of shRNA can interfere with short-term actions of ANG II. angiotensin II; hypertension ANGIOTENSIN II (ANG II) is an intensely investigated peptide with regard to its role in blood pressure regulation and the pathogenesis of cardiovascular disease. The importance of ANG II is highlighted by the effectiveness of drugs used clinically in the treatment of hypertension that target the ANG II pathway. Acute administration of ANG II increases blood pressure, largely by constricting vascular smooth muscle and increasing peripheral resistance. In addition, circulating ANG II increases blood pressure through neurogenically mediated mechanisms during acute and long-term ANG II exposure (9,22,28,33,43).In order for ANG II to stimulate neurally mediated increases in blood pressure, ANG II must act at angiotensin type 1 (AT 1 ) receptors (AT 1 Rs) in regions of the brain that recognize changes in circulating hormones, since ANG II does not cross the blood-brain barrier. However, circulating ANG II stimulates AT 1 Rs (10) in specifi...

Angiotensin II acting on brain AT1 receptors induces adrenaline secretion and pressor responses in the rat

“…In the hypothalamus, the paraventricular nucleus (PVN) has been considered as a regulatory centre of the central sympatho-adrenomedullary outflow4344. Actually, microinjected AngII into the PVN increased mean blood pressure45 and specific knockdown of AT 1a receptors in the PVN by infusion of interfering RNA against the receptors prevents hypertension induced by AngII treated peripherally4647. These findings suggest a possibility that the angiotensinergic system in the PVN is critical for AngII-induced elevation of blood pressure and also for the central sympatho-adrenomedullary outflow.…”

Artificial microRNA interference targeting AT1a receptors in paraventricular nucleus attenuates hypertension in rats

“…12 It was reported that adenoviruses encoding AT 1a small hairpin (shRNA) in the PVN in normal rats blunted the acute Ang II-induced elevation in MAP, but had no significant effect on basal MAP. 14 We speculate that the enhanced AT 1a R activity in the PVN has an important pathogenical role in triggering and sustaining the hypertension.…”

“…13 Microinjection of adenoviruses encoding AT 1a R small hairpin RNA into the PVN inhibits acute increases in arterial blood pressure but had no significant effects on the basal arterial pressure in normal rats. 14 However, it remains unknown whether gene silence of the AT 1a R in the PVN has beneficial effects on hypertension. The present study was designed to determine whether silencing of the AT 1a R in the PVN by artificial microRNA (amiRNA) interference attenuates the hypertension and sympathetic activity, and improves the cardiovascular remodeling in SHR.…”

Nitric oxide synthase, ADMA, SDMA, and nitric oxide activity in the paraventricular nucleus throughout the etiology of renal wrap hypertension

“…A: PVN adenoviral (Ad) eNOS administration had no effect on baseline blood pressure (V1-V6); however, Ad eNOS-treated wrap rats had a significantly blunted increase in blood pressure (days 0 -30). In addition, wrap Ad eNOS-treated rats were not significantly different from sham animals at the beginning of the treatment protocol (days 0 -3) or at the conclusion of the experiment (days [23][24][25][26][27][28][29][30]. B: PVN Ad eNOS administration had no effect on baseline blood pressure (V1-V6); however, during the beginning of the sham/renal wrap protocol, there was a significant difference in heart rate (days 2-5) in wrap Ad eNOS-treated rats compared with wrap Ad LacZ-treated rats.…”

“…These experiments confirmed that eNOS was expressed within the PVN in Ad eNOS-treated rats; however, due to the nature of limited to no eNOS being present during naive conditions, quantification of expression was not possible. A previous study (28), using an angiotensin type 1 receptor dominant negative Ad, demonstrated specific PVN targeting of Ad viruses.…”