Ang II-induced Blood Pressure Research Articles

Matrix metalloproteinase-2 knockout prevents angiotensin II-induced vascular injury.

Matrix metalloproteinases (MMPs) have been implicated in the development of hypertension in animal models and humans. Mmp2 deletion did not change Ang II-induced blood pressure (BP) rise. However, whether Mmp2 knockout affects angiotensin (Ang) II-induced vascular injury has not been tested. We sought to determine whether Mmp2 knockout will prevent Ang II-induced vascular injury. A fourteen-day Ang II infusion (1000 ng/kg/min, SC) increased systolic BP, decreased vasodilatory responses to acetylcholine, induced mesenteric artery (MA) hypertrophic remodelling, and enhanced MA stiffness in wild-type (WT) mice. Ang II enhanced aortic media and perivascular reactive oxygen species generation, aortic vascular cell adhesion molecule-1 and monocyte chemotactic protein-1 expression, perivascular monocyte/macrophage and T cell infiltration, and the fraction of spleen activated CD4+CD69+ and CD8+CD69+ T cells, and Ly-6Chi monocytes. Study of intracellular signalling showed that Ang II increased phosphorylation of epidermal growth factor receptor and extracellular-signal-regulated kinase 1/2 in vascular smooth muscle cells isolated from WT mice. All these effects were reduced or prevented by Mmp2 knockout, except for systolic BP elevation. Ang II increased Mmp2 expression in immune cells infiltrating the aorta and perivascular fat. Bone marrow (BM) transplantation experiments revealed that in absence of MMP2 in immune cells, Ang II-induced BP elevation was decreased, and that when MMP2 was deficient in either immune or vascular cells, Ang II-induced endothelial dysfunction was blunted. Mmp2 knockout impaired Ang II-induced vascular injury but not BP elevation. BM transplantation revealed a role for immune cells in Ang II-induced BP elevation, and for both vascular and immune cell MMP2 in Ang II-induced endothelial dysfunction.

Abstract 083: γ/δ T Cells Play a Role in Development of Hypertension

Objective: Both innate antigen-presenting cells and the adaptive immune system have been shown to play a role in the development of hypertension. Nevertheless, the T cell subsets involved in the pathophysiology of hypertension remains unclear. There is a small subset of “innate-like” T cells expressing the γ/δ T cell receptor (TCR) rather than the α/β TCR that could play a role bridging the innate and adaptive immune systems. We previously observed that angiotensin (Ang) II caused an increase in number and activation of γ/δ T cells and Ang II-induced systolic blood pressure (SBP) rise and vascular injury were blunted in Tcr δ -/- mice, which are devoid of γ/δ T cells. In order to further characterize the role of γ/δ T cells in hypertension, we determined whether Ang II-effects would be blunted by antibody-induced depletion of γ/δ T cells. In addition, we tested whether SBP in human could be predicted by combining the expression of genes encoding TCRGC (TCR gamma constant region) and pro-inflammatory markers of γ/δ T cells in peripheral blood mononuclear cells (PBMC). Method and Results: Thirteen to 15-week old male C57BL/6 wild-type (WT) mice were infused with Ang II (490 ng/kg/min, SC) for 14 days and injected IP with anti-γ/δ TCR or control isotype antibodies 1 day before and at day 6 of Ang II infusion. Depletion of γ/δ T cells decreased SBP (147±2 vs 167 ± 3 mm Hg, P <0.05) and restored mesenteric artery relaxation responses to acetylcholine (E max : 90±4 vs 62 ± 8%, P <0.05) compared to isotype antibody-treated mice. Using the SBP data and the PBMC gene expression profile (GSE12288) of 222 human subjects, we predicted with a supervised machine learning approach SBP by combining the gene expression of TCRGC and pro-inflammatory makers including interleukin-17A, interferon-γ and their receptors (R=0.23, P <0.001). Conclusion: Antibody-induced depletion further demonstrates the role of γ/δ T cells in Ang II-induced SBP elevation and vascular injury. Prediction of SBP using PBMC gene expression of γ/δ T cells and pro-inflammatory markers suggests that γ/δ T cells contribute to the development of human hypertension.

Abstract P343: Exercise-induces Mitochondrial Remodeling Prevents Angiotensin II-induced High Blood Pressure

Objective: Regular practice of exercise is one of the most effective non-pharmacological interventions that improve vascular health, which is thought to be mediated by a repeated exposure of vessel walls to increased hemodynamic shear stress. The objective of this study was to investigate the effect of exercise preconditioning on endothelial mitochondria in an Ang II-induced hypertension model. Methods: In in vitro experiments, human aortic endothelial cells (HAECs) pre-exposed to laminar shear stress (LSS) (20 dyne/cm 2 , 48h) or situated under static flow were incubated with Ang II (100 nM, 2-6 h). In in vivo experiments, mice were singly housed with or without a voluntary running wheel for 7 weeks. Ang II (1 mg/kg per day) was infused using an osmotic pump for the last 2 weeks. Saline was used as a control. Results: Significant increase in the expression levels of key genes related to mitochondrial biogenesis and dynamics were observed under shear stress conditions. Mitochondrial content determined by mtDNA content and immunostaining were higher (2-fold, P < 0.01) in the shear-exposed cells. en face staining showed significantly higher mitochondrial content in the conduit and muscle feed arteries from exercise-trained mice compared with sedentary controls ( N = 10, P < 0.01) but not in the mesenteric arteries. Interestingly, LSS preconditioning attenuated Ang II-induced mitochondrial dysfunction in HAECs, which was evidenced by decreased mitoROS generation, increased ΔΨm, and reduced mtDNA damage. Likewise, in aortic tissues, Ang II-induced mitochondrial phenotypic changes (i.e. mitoROS production, mtDNA damage and ΔΨm reduction) were significantly reduced in exercise-preconditioned mice compared to sedentary controls. Moreover, exercise preconditioning completely blocked Ang II-induced blood pressure elevation assessed by telemetry (MAP mmHg: 160.5 ± 1.5 vs 115.0 ± 11.4). Conclusion: Taken together, high-magnitude LSS improves endothelial function by enhancing mtDNA integrity and mitochondrial function. These findings further support the idea that aerobic exercise is a prominent life-style modification strategy to prevent hypertension by targeting dysfunctional mitochondria in the vessel wall.

Abstract P601: Matrix Metalloproteinase 2 Plays An Important Role In Angiotensin Ii-induced Vascular Injury Mediated In Part Through Epidermal Growth Factor Receptor Activation In Vascular Smooth Muscle Cells

Background: Matrix metalloproteinase 2 (MMP2) is involved in cardiovascular disease. Whether MMP2 plays a role in hypertension and vascular damage is unknown. We hypothesized that Mmp2 knockout will prevent angiotensin (Ang) II-induced blood pressure (BP) rise and vascular injury. Methods: Ten to 12-week-old male Mmp2 knockout (Mmp2-/-) and wild-type (WT) mice were infused with Ang II (1000 ng/kg/min, SC) for 14 days. Systolic BP was measured by telemetry, mesenteric arteries (MA) endothelial function and vascular remodeling by pressurized myography. In aortic wall or perivascular fat (PVAT), reactive oxygen species (ROS) generation was determined using dihydroethidium staining, and vascular cell adhesion protein 1 (VCAM-1), monocyte chemotactic protein-1 (MCP-1) expression and monocyte/macrophage infiltration by immunofluorescence. Spleen T cells and monocyte profile were assessed by flow cytometry. Vascular smooth muscle cells (VSMCs) were isolated from MA of WT and Mmp2 knockout mice, stimulated 5 min with 100 nM Ang II and epidermal growth factor receptor (EGFR) phosphorylation measured by Western-Blotting. Results: Ang II increased Systolic BP (172±7 vs 122±3, P<0.01), decreased MA vasodilatory responses to acetylcholine (33±5% vs 83±3%, P<0.01) and increases MA media-to-lumen ratio (5±0% vs 3±0%, P<0.01), media cross-sectional area (7224±467 vs 5345±336 μm2, P<0.05), and stiffness (P<0.01), as shown by a leftward shift of the stress/strain relationship, in WT. Furthermore, Ang II enhanced aortic ROS generation (73±11 vs 6±1 RFU/μm2, P<0.01), aortic VCAM-1 (17±3 vs 5±3 RFU/μm2, P<0.01) and MCP-1 expression (71±14 vs 11±3 RFU/μm2, P<0.01) and PVAT monocyte/macrophage infiltration (32±5 vs 4±0 RFU/μm2, P<0.05), and spleen activated CD4+CD69+ and CD8+CD69+ T cells and pro-inflammatory Ly-6Chi monocytes (17±2 vs 10±1%, 11±1 vs 5±1% and 53±6 vs 25±2%, respectively, P<0.05) in WT. Ang II increased EGFR phosphorylation in VSMCs in vitro (1.91±0.19 vs 1.0±0.0%, P<0.05). Mmp2 knockout prevented or reduced all of the above except BP elevation (P<0.05). Conclusion: MMP2 plays an important role in Ang II-induced vascular injury, which could be mediated at least in part through EFGR activation in VSMCs.

Abstract P617: Angiotensin II-induced Hypertension And Vascular Injury Is Mediated By Gamma/delta T Cells

Objective: Both innate antigen presenting cells and the adaptive immune system have been shown to play a role in the development of hypertension. Nevertheless, the T cell subset involved in the pathophysiology of hypertension remains unclear. There is a small subset of “innate-like” T cells expressing gamma/delta T cell receptor (TCR) rather than the alpha/beta TCR that could play a role in bridging between the innate and adaptive immune systems. However, it is unknown whether gamma/delta T cells contribute to development of hypertension. Method/Results: Thirteen to 15 week-old male C57BL/6 wild-type and Tcrd-/- mice, which are devoid of gamma/delta T cells, were infused or not with angiotensin (Ang) II (490 ng/kg/min, SC) for 7 or 14 days (n=4-9). Telemetric blood pressure, mesenteric artery endothelial function and vascular remodeling by pressurized myography and spleen T cell profile by flow cytometry were evaluated. Fourteen days of Ang II increased systolic blood pressure (167±4 vs 125±2 mmHg, P≤0.01) in wild-type compared to control mice. The frequency of gamma/delta T cells (6±1% vs 3±1%, P≤0.05) and activated (CD69+) gamma/delta T cells (11±1% vs 7±1%) was increased after 7 days of Ang II, and 7 days later were respectively unchanged or further increased (24±2% vs 10±1%) in wild-type compared to control mice. Ang II decreased mesenteric artery relaxation responses to acetylcholine (51±5% vs 88±3%, P≤0.01) and increased media/lumen (5±1 vs 3±0%, P≤0.01) in wild-type mice compare to controls. No gamma/delta T cells were detected in Tcrd-/- treated or not with Ang II. All the above Ang II effects were abrogated in Tcrd-/- mice. Conclusion: These data suggest that gamma/delta T cells mediate Ang II-induced blood pressure rise and vascular injury. Gamma/delta T cells could be key immune cells bridging innate and adaptive immune responses during the development of hypertension.

Endocannabinoid-mediated modulation of Gq/11 protein-coupled receptor signaling-induced vasoconstriction and hypertension

Activation of G protein-coupled receptors (GPCRs) can induce vasoconstriction via calcium signal-mediated and Rho-dependent pathways. Earlier reports have shown that diacylglycerol produced during calcium signal generation can be converted to an endocannabinoid, 2-arachidonoylglycerol (2-AG). Our aim was to provide evidence that GPCR signaling-induced 2-AG production and activation of vascular type1 cannabinoid receptors (CB1R) is capable of reducing agonist-induced vasoconstriction and hypertension.Rat and mouse aortic rings were examined by myography. Vascular expression of CB1R was demonstrated with immunohistochemistry. Rat aortic vascular smooth muscle cells (VSMCs) were cultured for calcium measurements and 2-AG-determination. Inhibition or genetic loss of CB1Rs enhanced vasoconstriction induced by angiotensin II (AngII) or phenylephrine (Phe), but not by prostaglandin(PG)F2α. AngII-induced vasoconstriction was augmented by inhibition of diacylglycerol lipase (tetrahydrolipstatin) and was attenuated by inhibition of monoacylglycerol lipase (JZL184) suggesting a functionally relevant role for endogenously produced 2-AG. In Gαq/11-deficient mice vasoconstriction was absent to AngII or Phe, which activate Gq/11-coupled receptors, but was maintained in response to PGF2α. In VSMCs, AngII-stimulated 2-AG-formation was inhibited by tetrahydrolipstatin and potentiated by JZL184. CB1R inhibition increased the sustained phase of AngII-induced calcium signal. Pharmacological or genetic loss of CB1R function augmented AngII-induced blood pressure rise in mice.These data demonstrate that vasoconstrictor effect of GPCR agonists is attenuated via Gq/11-mediated vascular endocannabinoid formation. Agonist-induced endocannabinoid-mediated CB1R activation is a significant physiological modulator of vascular tone. Thus, the selective modulation of GPCR signaling-induced endocannabinoid release has a therapeutic potential in case of increased vascular tone and hypertension.

Abstract 002: Activation of AT1 receptors on Dendritic Cells Restrains Angiotensin II-Dependent Hypertension Through a CCR7-dependent Mechanism

Dendritic cells (DCs) trigger an adaptive immune response by presenting processed antigens to T lymphocytes. Given the emerging importance of adaptive immunity in hypertension, we posited that DCs may sample neoantigens in the kidney in order to prime pro-hypertensive T cells. Using CD11c-Cre mT/mG mice in which DCs fluoresce green, we detected robust green signals within the kidney after 2 wks of angiotensin (Ang) II-induced hypertension, confirming infiltration of DCs into the hypertensive kidney. As activation of type 1 angiotensin (AT1) receptors on other immune cell lineages has been shown to alter inflammatory responses, we explored the role of the DC AT1 receptor in blood pressure regulation by generating mice with DC-specific deletion of the AT1A receptor (CD11c Cre+ Agtr1aflox/flox = DC KO) and littermate controls (Agtr1aflox/flox = WT). Compared to WTs, the DC KOs had an ≈87% reduction in AT1A receptor mRNA expression in DCs (p<0.0001) but preserved AT1A expression in B and T lymphocytes, kidney, and heart (p=NS). Next, we infused uni-nephrectomized DC KO mice and wild-type (WT) controls with Ang II (500ng/kg/min) for 4 wks. At baseline, the mean arterial blood pressure (MAP) was similar in WT and DC KO mice (123±2 vs. 126±2 mm Hg; p=NS). By contrast, after the 1st week of Ang II infusion, DC KO mice had markedly exaggerated MAP elevations compared to WTs (174±4 vs. 158±5 mm Hg; p=0.026). Expression of the chemokine receptor CCR7 on mature DCs and T cells directs both cell lineages to the lymph node where the DC can display a processed antigen and activate the T cell. We detected higher levels of CCR7 mRNA in the kidneys from the Ang II-infused DC KOs compared to WTs (2.98±0.90 vs. 1.00±0.16 au; p=0.04), and posited that enhanced DC priming of T cells in the DC KOs contributed to their exaggerated hypertension. Consistent with this possibility, uni-nephrectomized CCR7-deficient (KO) mice had a significantly blunted chronic hypertensive response to Ang II (165±4 vs. 178±2 mm Hg; p=0.03) and ameliorated albuminuria (2.1±0.2 vs. 3.7±0.8 mg/24hrs; p=0.02) versus WT controls. We conclude from these data that stimulation of AT1 receptors on DCs constrains Ang II-induced blood pressure elevation, possibly by limiting the CCR7-dependent activation of T lymphocytes by DCs.

Proximal tubule-dominant transfer of AT(1a) receptors induces blood pressure responses to intracellular angiotensin II in AT(1a) receptor-deficient mice.

The role of intracellular ANG II in proximal tubules of the kidney remains poorly understood. We tested the hypothesis that proximal tubule-dominant transfer of AT(1a) receptors in the cortex mediates intracellular ANG II-induced blood pressure responses in AT(1a) receptor-deficient (Agtr1a-/-) mice. A GFP-tagged AT(1a) receptor, AT(1a)R/GFP, and an enhanced cyan fluorescent intracellular ANG II fusion protein, ECFP/ANG II, were expressed in proximal tubules of Agtr1a-/- mouse kidneys via the adenoviral transfer using a sodium and glucose cotransporter 2 promoter. Transfer of AT(1a)R/GFP alone or with ECFP/ANG II induced proximal tubule-dominant expression of AT(1a)R/GFP and/or ECFP/ANG II with a peak response at 2 wk. No significant AT(1a)R/GFP and/or ECFP/ANG II expression was observed in the glomeruli, medulla, or extrarenal tissues. Transfer of AT(1a)R/GFP alone, but not ECFP/ANG II, increased systolic blood pressure by 12 ± 2 mmHg by day 14 (n = 9, P < 0.01). However, cotransfer of AT(1a)R/GFP with ECFP/ANG II increased blood pressure by 18 ± 2 mmHg (n = 12, P < 0.01). Twenty-four hour urinary sodium excretion was decreased by day 7 with proximal tubule-dominant transfer of AT(1a)R/GFP alone (P < 0.01) or with AT(1a)R/GFP and ECFP/ANG II cotransfer (P < 0.01). These responses were associated with twofold increases in phosphorylated ERK1/2, lysate, and membrane NHE-3 proteins in freshly isolated proximal tubules (P < 0.01). By contrast, transfer of control CMV-GFP (a recombinant human adenovirus type 5 expresses enhanced green fluorescent protein under the control of a cytomegalovirus (CMV) promoter), ECFP/ANG II, or a scrambled control ECFP/ANG IIc alone in proximal tubules had no effect on all indices. These results suggest that AT(1a) receptors and intracellular ANG II in proximal tubules of the kidney play an important physiological role in blood pressure regulation.

Heat shock proteins 27 and 70 regulating angiotensin II-induced NF-κB: a possible connection to blood pressure control?

Heat shock proteins (HSPs) are critical for cell survival and have several mechanisms of action. HSPs regulate protein folding, suppress apoptosis, and regulate anti-oxidative activity. In addition, HSPs are involved in the regulation of the pro-inflammatory transcription factor nuclear factor (NF)-kappaB. When angiotensin (Ang) II is infused into rats, there is a significant increase in systolic blood pressure, and NF-kappaB is activated in the heart. If rats are heat shocked to induce the heat shock response and HSPs before Ang II infusion, there is a significant suppression of both the Ang II-induced increase in blood pressure and NF-kappaB activation in the heart. Although the role of specific HSPs in the regulation of NF-kappaB is unclear, several HSPs, including Hsp27 and Hsp70, are thought to be involved in the regulation of Ang II-induced NF-kappaB. The role of Hsp27 and Hsp70 in NF-kappaB activation is reviewed here, along with evidence suggesting that HSPs regulate Ang II-induced blood pressure through the regulation of NF-kappaB.

Green Tea Attenuates Angiotensin II-Induced Cardiac Hypertrophy in Rats by Modulating Reactive Oxygen Species Production and the Src/Epidermal Growth Factor Receptor/Akt Signaling Pathway1,

We previously documented a clear-cut antihypertensive effect of green teat extract (GTE), which was associated with correction of endothelial dysfunction and prevention of left ventricular hypertrophy in an angiotensin II (Ang II)-dependent model of hypertension, but the molecular mechanisms remain to be defined. As several effects of Ang II involve production of reactive oxygen species (ROS) and activation of 2nd messengers, such as mitogen-activated protein kinase (MAPK) and Akt, we investigated the effect of GTE on these signal transduction pathways in Ang II-treated rats. Rats were treated for 2 wk with Ang II infusion (700 μg·kg−1·d−1; n = 6, via osmotic minipumps), Ang II plus GTE (6 g/L) dissolved in the drinking water; n = 6), or vehicle (n = 6) to serve as controls. Blood pressure was monitored by telemetry throughout the study. The activation and expression of NAD(P)H oxidase subunits, protein kinase C isoforms, Src, epidermal growth factor receptor (EGFR), Akt, and MAPK were determined in the heart in vitro through immunoprecipitation and western blot analysis with specific antibodies. NAD(P)H oxidase enzymatic activity was measured by cytochrome c reduction assay. GTE blunted Ang II-induced blood pressure increase and cardiac hypertrophy. In Ang II-treated rats, GTE decreased the expression of the NAD(P)H oxidase subunit gp91phox and the translocation of Rac-1, as well as NAD(P)H oxidase enzymatic activity. Furthermore, it specifically reduced Ang II-induced Src, EGFR, and Akt phosphorylation. These results show that GTE blunts Ang II-induced cardiac hypertrophy specifically by regulating ROS production and the Src/EGFR/Akt signaling pathway activated by Ang II.

Gender differences in vascular disease: not a simple explanation

Gender differences in vascular disease: not a simple explanation

Synergistic vascular protective effects of combined low doses of PPARα and PPARγ activators in angiotensin II‐induced hypertension in rats

Protective cardiovascular effects of peroxisome proliferator activated receptor (PPAR)alpha and PPARgamma activators have been demonstrated. If used as vasoprotective agents in high risk vascular patients rather than for their metabolic benefits, these agents could be associated with unwanted side effects. As a proof of concept to support the use of combined low doses of PPARalpha and PPARgamma as vascular protective agents in high risk vascular patients, we tested the hypothesis that combined low doses of PPARalpha (fenofibrate) and PPARgamma (rosiglitazone) activators would provide vascular protective benefits similar to full individual doses of these PPAR agonists. Male Sprague-Dawley rats infused with Ang II (120 ng kg(-1) min(-1)) were treated with rosiglitazone (1 or 2 mg kg(-1) day(-1)) alone or concomitantly with fenofibrate (30 mg kg(-1) day(-1)) for 7 days. Thereafter, vessels was assessed on a pressurized myograph, while NAD(P)H oxidase activity was determined by lucigenin chemiluminescence. Inflammation was evaluated using ELISA for NFkappaB and Western blotting for adhesion molecules. Ang II-induced blood pressure increase, impaired acetylcholine-induced vasorelaxation, altered vascular structure, and enhanced vascular NAD(P)H oxidase activity and inflammation were significantly reduced by low dose rosiglitazone+fenofibrate. Combined low doses of PPARalpha and PPARgamma activators attenuated development of hypertension, corrected vascular structural abnormalities, improved endothelial function, oxidative stress, and vascular inflammation. These agents used in low-dose combination have synergistic vascular protective effects. The clinical effects of combined low-dose PPARalpha and PPARgamma activators as vascular protective therapy, potentially with reduced side-effects and drug interactions, should be assessed.

Effect of an avocado oil-rich diet over an angiotensin II-induced blood pressure response

We studied the effect of an avocado oil-rich diet on (1) the blood pressure response to angiotensin II (AngII) and (2) the fatty acid composition of cardiac and renal membranes on male Wistar rats. The avocado oil-rich diet induced a slightly higher AngII-induced blood pressure response in the rats as compared to the control rats. In cardiac microsomes, avocado oil induced an increase in oleic acid content (13.18 ± 0.33% versus 15.46 ± 0.59%), while in renal microsomes, the oil decreased α-linolenic acid content (0.34 ± 0.02% versus 0.16 ± 0.12%), but increased the arachidonic acid proportion (24.02 ± 0.54% versus 26.25 ± 0.54%), compared to control. In conclusion, avocado oil-rich diet modifies the fatty acid content in cardiac and renal membranes in a tissue-specific manner. The rise in renal arachidonic acid suggests that diet content can be a key factor in vascular responses.

Small artery mechanics in hyperhomocysteinemic mice: effects of angiotensin II.

Elevated plasma homocysteine has been associated with cardiovascular disease, although a causal relationship is unclear. The purpose of this study was to evaluate whether mild hyperhomocysteinemia (H-Hcy) may increase vascular stiffness of small arteries. Wild-type (+/+) and heterozygous (+/-) methylenetetrahydrofolate reductase (Mthfr) knockout mice, a new model of mild H-Hcy, were treated with vehicle or angiotensin (Ang) II infusion (400 ng/kg per min s.c.). Second-order mesenteric arteries were studied on pressurized myograph. They were exposed to intraluminal pressures ranging from 3 to 140 mmHg. Media thickness and lumen diameter were measured at each pressure level to determine wall mechanical properties. Collagen type I/III and elastin deposition in the vascular wall were evaluated by confocal immunofluorescence microscopy. Media-to-lumen ratio was similar in Mthfr and Mthfr mice, and significantly increased by Ang II. The stress-strain relationship was shifted to the left in small mesenteric arteries from Mthfr compared to Mthfr mice, indicating that mild H-Hcy is associated with stiffer vessels. Ang II treatment in Mthfr mice enhanced the leftward shift in the stress-strain relationship and significantly increased the elastic modulus, suggesting the presence of stiffer wall components in small arteries in these animals. Increased collagen type I/III accumulation and decreased elastin content in the media of mesenteric arteries was noted in Mthfr compared to Mthfr mice. Ang II infusion augmented vascular collagen deposition in both groups, more substantially in Mthfr mice. Mild hyperhomocysteinemia is associated with stiffer small arteries with increased collagen deposition in the media. These changes are accentuated by Ang II-induced blood pressure elevation.

AT 1 receptors mediate pressor responses induced by angiotensin II in the periaqueductal gray area of rats

Microinjection of angiotensin II (ANGII) (0.01 to 1 nmol) into the periaqueductal gray area (PAG) of anaesthetised rats caused dose-dependent increases in blood pressure. Preinjection (10 min before) of losartan (a selective non-peptide AT 1 receptor antagonist; 50 nmol) to the PAG reduced the pressor response to ANGII whereas PD123319 (a selective non-peptide AT 2 receptor antagonist; 50 nmol) did not affect the ANGII-induced hypertension. Thus, our data suggest that the activation of AT 1 but not AT 2 receptors mediates ANGII-induced blood pressure changes in the PAG area.

Differential regulation of central vasopressin in transgenic rats harboring the mouse Ren-2 gene.

The transgenic (TG) rat carrying the mouse renin gene (mRen-2d) has provided a unique opportunity to explore central interactions between the brain renin-angiotensin (RAS) and vasopressin (AVP) systems. To evaluate the hypothalamic vasopressin axis in the TG rat, we measured the central nervous system concentrations of AVP and determined the effect of angiotensin II (ANG II) and its NH2-terminal heptapeptide [angiotensin-(1-7)] on blood pressure, heart rate, and AVP release using brain microdialysis. Intracerebroventricular infusion of ANG II or ANG-(1-7) in control rats increased local AVP release from the paraventricular and supraoptic nuclei. The ANG II infusion was associated with a significant increase in blood pressure not observed with ANG-(1-7). In contrast, the angiotensin peptide-induced central AVP responses and the ANG II-induced blood pressure increase were absent in the TG animal. The plasma AVP responses to ANG II and ANG-(1-7) were comparable in the control and TG rats. The TG rats exhibited a 22-fold higher level of AVP in the dorsal lower brain stem but had lower AVP levels in the posterior pituitary and the median eminence compared with control rats. These results suggest that insertion of the mouse renin gene into the rat genome leads to alterations in the AVP axis in terms of AVP peptide content and angiotensin-induced cardiovascular and AVP responses.

Blood pressure effects of iontophoretically applied bioactive hormones in the anterior forebrain of the rat

In the course of electrophysiological investigations using iontophoresis, we observed that in specific regions of the forebrain even these minute applications of peptide and steroid hormones can influence systemic blood pressure. In urethan-anesthetized male Wistar rats, with a catheter in the femoral artery, iontophoretic application of the peptide hormones angiotensin II (ANG II), vasopressin (AVP), and atrial natriuretic peptide (ANP) and the steroid hormone aldosterone (ALDO) was effective at locations in the midline septum, the triangularis nucleus of the septum, and the subfornical organ (SFO). Increases in blood pressure (of up to 15 mmHg) were observed after ANG II and AVP, decreases after ALDO, and either an increase or a decrease, depending on the location, after ANP. There was no clear evidence of an antagonistic effect of ANP on ANG II-induced neuronal or blood pressure responses. In addition to demonstrating the potency of these hormones even when they are restricted to tiny volumes of tissue, the present results demonstrate that the medial ventral region of the anterior forebrain may be included in the same baroreceptive circuit as the SFO (and organ vasculosum of the lamina terminalis) and hence be involved in the regulation of blood volume and perhaps in the sensing of and corrective responses to extracellular thirst.

Acute hypertensive response to saline induced by vanadate, an insulinomimetic agent.

To investigate whether the reported insulin-like properties of vanadate may have hypertensinogenic actions in Sabra rats. Comparison of [3H]-deoxyglucose muscle uptake as well as blood pressure and its response to acute volume expansion and pressors infusions in 16 vanadate-treated (VT) and 12 control rats. Rats drank either tap water or 0.2 g/l vanadate for 4 weeks. A trace amount of [3H]-deoxyglucose was administered intravenously to evaluate its plasma half-life and tissue uptake. Intra-arterial blood pressure was recorded in response to acute intravenous saline (4 ml/100 g body weight) and to incremental bolus injections of noradrenaline and angiotensin II (Ang II). Skeletal muscle uptake of [3H]-deoxyglucose was significantly higher in VT than in control rats. There was no difference between the blood pressure of VT or control rats; however, 2 h after saline loading the mean intra-arterial blood pressure was significantly higher in VT than in control rats. The Ang II-induced blood pressure rise was also significantly higher in VT rats. The insulin-like activity of vanadate may be associated with salt-sensitive hypertension.

An Angiotensin with Prolonged Action and Blood Pressure-Lowering Properties

[Sar1,Phe(Br5)8] angiotensin II (Br5Ang II) is a specific, quasi-irreversible antagonist of angiotensin II (Ang II) in vitro. In vivo, this compound is a very potent, Ang II-specific antagonist with a very long duration of action against Ang II-induced blood pressure (BP) increases. In the "low-sodium" dog, this compound induces a prolonged BP reduction during and after intravenous infusion at doses comparable to cilazapril, a potent ACE inhibitor. The physicochemical and pharmacokinetic behavior of this peptide was therefore assessed to understand and interpret the prolonged antagonistic and antihypertensive activity of this peptide. Binding studies using beef adrenocortical membranes indicated specific binding of Br5Ang and related analogues to Ang II receptors with a Kd of 1.41 x 10(-9) M against iodinated [Sar1, D-Phe8]Ang II, a standard radioligand antagonist. Iodinated Br5AngII exhibited a very high degree of nonspecific binding to the membranes. It had an octanol-water partitioning coefficient of log P of + 0.903, a coefficient 84-fold higher than for [125I][Sar1, D-Phe8]Ang II. Association kinetics of [125I]Br5Ang II were similar to the standard ligand [125I] [Sar1, D-Phe8]Ang II, but the half-life of dissociation was four times higher (60 vs. 15 min at 20 degrees C). Molecular modeling indicates a practically identical conformational behavior of both peptides, Br5Ang II and [Sar1, D-Phe8]Ang II but with an expanded hydration shell over the Br5 residue. It is concluded that the prolonged duration of action is due to the increased hydrophobicity of the peptide, which leads to a slow dissociation from the Ang II receptor.(ABSTRACT TRUNCATED AT 250 WORDS)