[Show abstract][Hide abstract] ABSTRACT: AT1 receptor subtype a (AT1Ra) expression is increased in the nucleus of the solitary tract (NTS) in spontaneously hypertensive rat (SHR) compared with Wistar Kyoto controls. However, the chronic role of AT1Ra in the NTS for cardiovascular control is not well understood. In this study, we investigated the hypothesis that the NTS AT1Ra is involved in the neural regulation of the peripheral inflammatory status and linked with hypertension. Transduction of brain neuronal cultures with recombinant adeno-associated virus type 2 (AAV2)-AT1R-small hairpin RNA (shRNA) resulted in a 72% decrease in AT1Ra mRNA and attenuated angiotensin II-induced increase in extracellular signal-regulated kinase 1/2 phosphorylation and neuronal firing. Specific NTS microinjection of AAV2-AT1R-shRNA vector in the SHR resulted in a ≈30 mm Hg increase in the mean arterial pressure compared with control vector-injected animals (Sc-shRNA: 154±4 mm Hg; AT1R-shRNA: 183±10 mm Hg) and induced a resetting of the baroreflex control of heart rate to higher mean arterial pressure. In addition, AAV2-AT1R-shRNA-treated SHRs exhibited a 74% decrease in circulating endothelial progenitor cells (CD90(+), CD4(-)/CD5(-)/CD8(-)) and a 300% increase in the circulating inflammatory cells, including CD4(+)(+)CD8(+), CD45(+)/3(+) T lymphocytes, and macrophages (CD68(+)). As a result, the endothelial progenitor cell/inflammatory cells ratio was decreased by 8- to 15-fold in the AT1R-shRNA-treated SHR. However, identical injection of AAV2-AT1R-shRNA into the NTS of Wistar Kyoto rats had no effect on mean arterial pressure and inflammatory cells. These observations suggest that increased expression of the AT1Ra in SHR NTS may present a counterhypertensive mechanism involving inflammatory/angiogenic cells.
[Show abstract][Hide abstract] ABSTRACT: Central hyperosmotic stimulation (HS) evokes increases in sympathetic nerve activity mediated by activation of angiotensin type 1 receptors in the hypothalamic paraventricular nucleus (PVN). Macrophage inhibitory migration factor (MIF) is an intracellular inhibitory regulator of angiotensin type 1 receptor-mediated actions of angiotensin II within neurons of the PVN. MIF mediates its actions via its intrinsic thiol-protein oxidoreductase activity. We demonstrate that intracerebroventricular injection of hypertonic saline into Sprague-Dawley rats elicits a significant (≈112%) increase in MIF mRNA expression in the PVN. Next, we evaluated the effect of viral-mediated expression of either MIF or [C60S]-MIF (which lacks thiol-protein oxidoreductase activity) in the PVN on the sympathoexcitation evoked by HS. We used a decorticate, arterially perfused in situ preparation of male Wistar rats (60 to 80 g). HS was induced by raising perfusate osmolality from 290 to 380 milliosmoles for 40 seconds. Seven to 10 days before experiments, rats were injected bilaterally (500 nL per side) with 0.9% saline (control) or with adenoassociated virus to express MIF, [C60S]-MIF, or enhanced green fluorescent protein in the PVN. HS produced sympathoexcitation in both the 0.9% saline and enhanced green fluorescent protein groups (sympathetic nerve activity increase of +27±4% and +25±4%, respectively; P<0.05), an effect that was not observed in the MIF group (+4±5%). Conversely, the HS-induced increase in sympathetic nerve activity was potentiated in the [C60S]-MIF group (+45±6%; P<0.05). We propose that MIF acting within the PVN is a major counterregulator of HS-induced sympathoexcitation, an effect that depends on thiol-protein oxidoreductase activity.
[Show abstract][Hide abstract] ABSTRACT: Despite overwhelming evidence of the importance of brain renin-angiotensin system (RAS), the very existence of intrinsic brain RAS remains controversial.
To investigate the hypothesis that the brain (pro)renin receptor (PRR) is physiologically important in the brain RAS regulation and cardiovascular functions.
PRR is broadly distributed within neurons of cardiovascular-relevant brain regions. The physiological functions of PRR were studied in the supraoptic nucleus (SON) because this brain region showed greater levels of PRR mRNA in the spontaneously hypertensive rats (SHR) compared with normotensive Wistar-Kyoto (WKY) rats. Adeno-associated virus (AAV)-mediated overexpression of human PRR in the SON of normal rats resulted in increases in plasma and urine vasopressin, and decreases in H(2)O intake and urine output without any effects on mean arterial pressure and heart rate. Knockdown of endogenous PRR by AAV-short hairpin RNA in the SON of SHRs attenuated age-dependent increases in mean arterial pressure and caused a decrease in heart rate and plasma vasopressin. Incubation of neuronal cells in culture with human prorenin and angiotensinogen resulted in increased generation of angiotensin I and II. Furthermore, renin treatment increased phosphorylation of extracellular signal-regulated kinase ½ in neurons from both WKY rats and SHRs; however, the stimulation was 50% greater in the SHR.
The study demonstrates that brain PRR is functional and plays a role in the neural control of cardiovascular functions. This may help resolve a long-held controversy concerning the existence of intrinsic and functional brain RAS.
Full-text · Article · Oct 2010 · Circulation Research