The Total Denervation of the Ischemic Kidney Induces Differential Responses in Sodium Transporters' Expression in the Contralateral Kidney in Goldblatt Rats.

The Goldblatt model of hypertension (2K-1C) in rats is characterized by renal sympathetic nerve activity (rSNA). We investigated the effects of unilateral renal denervation of the clipped kidney (DNX) on sodium transporters of the unclipped kidneys and the cardiovascular, autonomic, and renal functions in 2K-1C and control (CTR) rats. The mean arterial pressure (MAP) and rSNA were evaluated in experimental groups. Kidney function and NHE3, NCC, ENaCß, and ENaCγ protein expressions were assessed. The glomerular filtration rate (GRF) and renal plasma flow were not changed by DNX, but the urinary (CTR: 0.0042 ± 0.001; 2K-1C: 0.014 ± 0.003; DNX: 0.005 ± 0.0013 mL/min/g renal tissue) and filtration fractions (CTR: 0.29 ± 0.02; 2K-1C: 0.51 ± 0.06; DNX: 0.28 ± 0.04 mL/min/g renal tissue) were normalized. The Na+/H+ exchanger (NHE3) was reduced in 2K-1C, and DNX normalized NHE3 (CTR: 100 ± 6; 2K-1C: 44 ± 14, DNX: 84 ± 13%). Conversely, the Na+/Cl- cotransporter (NCC) was increased in 2K-1C and was reduced by DNX (CTR: 94 ± 6; 2K-1C: 144 ± 8; DNX: 60 ± 15%). In conclusion, DNX in Goldblatt rats reduced blood pressure and proteinuria independently of GRF with a distinct regulation of NHE3 and NCC in unclipped kidneys.

Creatine Supplementation in Type 2 Diabetic Patients: A Systematic Review of Randomized Clinical Trials.

Type 2 Diabetes Mellitus (DM) is the most common form of diabetes. The initial treatment of type 2 DM consists of the adoption of healthy lifestyle habits together with several classes of hypoglycemic agents. However, these medications are not always able to reduce the blood glucose levels in all patients. Therefore, creatine supplementation has emerged as a new putative candidate for type 2 DM treatment. This systematic review aimed to investigate the effects (benefits and harms) of creatine supplementation in patients with type 2 diabetes through a systematic review. The studies were searched in MEDLINE, EMBASE, LILACS, CENTRAL, SPORTDiscus, and CINAHL databases, without date or language restrictions. Methodological quality was assessed using the Cochrane risk-of-bias table. The certainty of the evidence was classified using the Grading of Recommendations Assessment, Development and Evaluation approach. Three randomized controlled trials (RCTs) were included (87 participants). Overall, the methodological quality was classified as unclear to a high risk of bias. Each trial compared creatine supplementation with a different control group (placebo, metformin, and glibenclamide). Creatine supplementation seems to be effective in decreasing glycemic levels and glycosylated hemoglobin concentrations compared to placebo. No difference was observed compared to metformin or glibenclamide with creatine, and all treatments were able to reduce blood glucose levels. No major adverse effects were observed. Based on the low certainty of evidence, creatine supplementation was shown to be a hypoglycemic intervention for patients with type 2 diabetes, without major adverse events reported. However, well- designed RCTs with larger sample sizes and long-term outcomes are needed to support this evidence.

Treatment with Mesenchymal Stem Cells Improves Renovascular Hypertension and Preserves the Ability of the Contralateral Kidney to Excrete Sodium.

BACKGROUND: Mesenchymal stem cells (MSC) improve renal function and renovascular hypertension in the 2-kidney 1-clip model (2K-1C). While MSC play an immunomodulatory role, induce neoangiogenesis, and reduce fibrosis, they do not correct sodium loss by the contra-lateral kidney. OBJECTIVES: We investigated the tubular function of both stenotic and contralateral kidneys and the effect of MSC treatment by evaluating diuresis, natriuresis, and the expression of the main water and sodium transporters. METHOD: Adult Wistar rats were allocated into four groups: control (CT), CT+MSC, 2K-1C, and 2K-1C+MSC. MSC (2 × 105) were infused through the tail vein 3 and 5 weeks after clipping. Systolic blood pressure (SBP) was monitored weekly by plethysmography. Six weeks after clipping, 24-hour urine and blood samples were collected for biochemical analysis. Gene expression of the Na/H exchanger-3, epithelial sodium channel, Na/K-ATPase, Na/K/2Cl cotransporter, and aquaporins 1 and 2 (AQP1 and AQP2) were analyzed by RT-PCR. Intrarenal distribution of AQP1 and AQP2 was analyzed by immunohistochemistry. RESULTS: In hypertensive 2K-1C animals, MSC prevented additional increases in BP. AQP1, but not AQP2, was suppressed in the contralateral kidney, resulting in significant increase in urinary flow rate and sodium excretion. Gene expressions of sodium transporters were similar in both kidneys, suggesting that the high perfusing pressure in the contralateral kidney was responsible for increased natriuresis. Contralateral hypertensive kidney showed signs of renal deterioration with lower GFR in spite of normal RPF levels. CONCLUSIONS: MSC treatment improved renal function and enhanced the ability of the contralateral kidney to excrete sodium through a tubular independent mechanism contributing to reduce SBP.

Renovascular hypertension: Effects of mesenchymal stem cells in the contralateral hypertensive kidney in rats.

Mesenchymal stem cells (MSC) induced neovascularization and improved renal morphology of the stenotic kidney in 2 kidneys-1 clip (2K-1C) model of renovascular hypertension. The present study evaluated the effects of MSC in the contralateral hypertensive kidney. Three weeks after left renal artery occlusion, MSC were injected into the tail vein of the 2K-1C rats. Renal function and morphology were analyzed in both kidneys. Labeled MSC were found in stenotic and contralateral kidneys. Hypertensive 2K-1C animals presented increased circulating levels of Angiotensin II (Ang II) and renin. MSC prevented the progressive increase of blood pressure and reduced circulating Ang II and renin levels. Stenotic kidney showed reduced renal plasma flow (RPF) and glomerular filtration rate (GFR), whereas the contralateral kidney had a tendency (p > 0.5) of reduction in GFR in spite of unchanged RPF. MSC treatment caused an improvement in GFR with no effect of on RPF in the stenotic kidney. Contralateral kidney showed increased diuresis and natriuresis that were even higher in MSC-treated animals, indicating that cell treatment improved the capacity of the contralateral kidney to excrete sodium. Contralateral kidney expressed higher levels of inflammatory cytokines (IL-6, TNF-α) and signs of fibrosis, which were attenuated by MSC treatment. MSC treatment improved the stenotic kidney function, and it was also beneficial to the contralateral hypertensive kidney because it improved the morphology and preserved its capacity to excrete sodium.

Mesenchymal stem cells and chronic renal artery stenosis.

Renal artery stenosis is the main cause of renovascular hypertension and results in ischemic nephropathy characterized by inflammation, oxidative stress, microvascular loss, and fibrosis with consequent functional failure. Considering the limited number of strategies that effectively control renovascular hypertension and restore renal function, we propose that cell therapy may be a promising option based on the regenerative and immunosuppressive properties of stem cells. This review addresses the effects of mesenchymal stem cells (MSC) in an experimental animal model of renovascular hypertension known as 2 kidney-1 clip (2K-1C). Significant benefits of MSC treatment have been observed on blood pressure and renal structure of the stenotic kidney. The mechanisms involved are discussed.

Mechanisms of renal sympathetic activation in renovascular hypertension.

NEW FINDINGS: What is the topic of this review? This review addresses the underlying mechanisms involved in sympathoexcitation during renovascular hypertension, focusing on the importance of increased oxidative stress in the paraventricular nucleus and rostral ventrolateral medulla. What advances does it highlight? Whether renal or autonomic dysfunction is the major contributor to systemic hypertension following a renovascular insult is still a matter of debate. Here, we take an integrative approach by describing the crosstalk between the kidney and brain. We show how changes in the CNS, and in sympathetic premotor neurons in particular, are activated by ischaemic renal disease in an experimental model of renovascular hypertension. This review addresses the underlying mechanisms involved in the sympathoexcitation in renovascular hypertension. We focus on the importance of increased oxidative stress in the paraventricular nucleus of hypothalamus (PVN) and rostral ventrolateral medulla (RVLM) for the autonomic dysfunction associated with renovascular hypertension in the two-kidney, one-clip (2K-1C) model. We found in 2K-1C rats, 6 weeks after clipping, a significant increase in the mRNA and protein expression of the angiotensin II type 1 receptor within the RVLM and PVN. In addition, mRNA from NADPH oxidase subunits (p47phox and gp91phox) was greater in the RVLM and PVN of 2K-1C rats than in a sham-operated group. However, CuZn superoxide dismutase gene expression in these regions was not changed, suggesting that excessive production of reactive oxygen species overwhelms any endogenous antioxidant system in the RVLM and PVN in renovascular hypertension. In fact, acute administration of tempol or vitamin C (either i.v. or directly into the PVN or RVLM) caused a significant decrease in blood pressure and renal sympathetic nerve activity in 2K-1C rats, but not in control animals. Thus, we suggest that an increase in the activity of RVLM and PVN neurons triggered by angiotensin II and oxidative stress is a major mechanism involved in the maintenance of sympathoexcitation of the cardiovascular system in renovascular hypertension.

Effects of mesenchymal stem cells in renovascular hypertension.

NEW FINDINGS: What is the topic of this review? The major topic of this review addresses the effects of mesenchymal stem cell treatment in renovascular hypertension. What advances does it highlight? This therapy may be a promising strategy to treat renovascular hypertension and its renal consequences in the near future. Renovascular hypertension induced by the two-kidney, one-clip technique is a renin-angiotensin system-dependent model that leads to renal vascular rarefaction, fibrosis and renal failure. Treatment of renovascular hypertension remains a challenge, and thus, new therapies are needed. In this report, we discuss the beneficial effects of mesenchymal stem cells on the reconstruction of the renal parenchyma of the stenotic kidney to improve vascular rarefaction and fibrosis. Mesenchymal stem cell therapy prevented the progressive increase in systolic arterial pressure, reduced sympathetic hyperactivity, improved renal morphology, induced neovascularization and reduced fibrosis in stenotic kidneys. Although this therapy may be a promising strategy to treat renovascular hypertension and its renal consequences, further studies are necessary to improve the efficiency of mesenchymal stem cells.

Revealing the role of the autonomic nervous system in the development and maintenance of Goldblatt hypertension in rats.

Despite extensive use of the renovascular/Goldblatt model of hypertension-2K-1C, and the use of renal denervation to treat drug resistant hypertensive patients, autonomic mechanisms that underpin the maintenance of this hypertension are important yet remain unclear. Our aim was to analyse cardiovascular autonomic function by power spectral density analysis of both arterial pressure and pulse interval measured continuously by radio telemetry for 6weeks after renal artery clipping. Mean arterial pressure increased from 106±5 to 185±2mmHg during 5weeks post clipping when it stabilized. A tachycardia developed during the 4th week, which plateaued between weeks 5 and 6. The gain of the cardiac vagal baroreflex decreased immediately after clipping and continued to do so until the 5th week when it plateaued (from -2.4±0.09 to -0.8±0.04bpm/mmHg; P<0.05). A similar time course of changes in the high frequency power spectral density of the pulse interval was observed (decrease from 13.4±0.6 to 8.3±0.01ms(2); P<0.05). There was an increase in both the very low frequency and low frequency components of systolic blood pressure that occurred 3 and 4weeks after clipping, respectively. Thus, we show for the first time the temporal profile of autonomic mechanisms underpinning the initiation, development and maintenance of renovascular hypertension including: an immediate depression of cardiac baroreflex gain followed by a delayed cardiac sympathetic predominance; elevated sympathetic vasomotor drive occurring after the initiation of the hypertension but coinciding during its mid-development and maintenance.

Mesenchymal stem cells (MSC) prevented the progression of renovascular hypertension, improved renal function and architecture.

Renovascular hypertension induced by 2 Kidney-1 Clip (2K-1C) is a renin-angiotensin-system (RAS)-dependent model, leading to renal vascular rarefaction and renal failure. RAS inhibitors are not able to reduce arterial pressure (AP) and/or preserve the renal function, and thus, alternative therapies are needed. Three weeks after left renal artery occlusion, fluorescently tagged mesenchymal stem cells (MSC) (2×10(5) cells/animal) were injected weekly into the tail vein in 2K-1C hypertensive rats. Flow cytometry showed labeled MSC in the cortex and medulla of the clipped kidney. MSC prevented a further increase in the AP, significantly reduced proteinuria and decreased sympathetic hyperactivity in 2K-1C rats. Renal function parameters were unchanged, except for an increase in urinary volume observed in 2K-1C rats, which was not corrected by MSC. The treatment improved the morphology and decreased the fibrotic areas in the clipped kidney and also significantly reduced renal vascular rarefaction typical of 2K-1C model. Expression levels of IL-1ß, TNF-α angiotensinogen, ACE, and Ang II receptor AT1 were elevated, whereas AT2 levels were decreased in the medulla of the clipped kidney. MSC normalized these expression levels. In conclusion, MSC therapy in the 2K-1C model (i) prevented the progressive increase of AP, (ii) improved renal morphology and microvascular rarefaction, (iii) reduced fibrosis, proteinuria and inflammatory cytokines, (iv) suppressed the intrarenal RAS, iv) decreased sympathetic hyperactivity in anesthetized animals and v) MSC were detected at the CNS suggesting that the cells crossed the blood-brain barrier. This therapy may be a promising strategy to treat renovascular hypertension and its renal consequences in the near future.

Losartan reduces oxidative stress within the rostral ventrolateral medulla of rats with renovascular hypertension.

BACKGROUND: Previous studies showed that the microinjection of antioxidants or the overexpression of superoxide dismutase within the rostral ventrolateral medulla (RVLM) reduces hypertension and sympathoexcitation in the 2-kidney, 1-clip (2K-1C) model. In this study, we hypothesized that angiotensin II (ANG II) type 1 receptor (AT1R) is involved in the oxidative stress within the RVLM and contributes to cardiovascular dysfunction in renovascular hypertension. METHODS: Losartan (30mg/kg/day, oral gavage) was administered for 7 consecutive days by week 5 after implantation of the clip (gap width = 0.2mm). Mean arterial pressure, baroreflex, and renal sympathetic nerve activity (rSNA) were evaluated. Superoxide production was evaluated by dihydroethidium (DHE) staining within the RVLM and within a control area. Systemic oxidative stress was characterized by measurement of thiobarbituric acid reactive substances (TBARS) and total glutathione (tGSH) in the blood. RESULTS: AT1R blockade significantly (P < 0.05) reduced hypertension by approximately 20% (n = 11) and sympathoexcitation to the kidneys by approximately 41% (n = 6) in the 2K-1C rats. Losartan treatment increased the baroreflex sensitivity of rSNA to pressor (67%) and depressor (140%) stimuli in the 2K-1C rats. AT1R blockade caused a significant (66%) reduction in DHE staining within the RVLM but not within the control area, reduced plasma TBARS (from 1.6±0.1 to 1.0±0.1 nmol/ml), and increased tGSH (from 3.4±0.4 to 5.2±0.3 µmol/g Hb) in the 2K-1C group only. CONCLUSIONS: Our findings suggest that the beneficial effects of ANG II blockade in renovascular hypertension are partly due to preferential reduction of oxidative stress in the RVLM.

Involvement of nitric oxide pathways in neurogenic pulmonary edema induced by vagotomy.

OBJECTIVE: The objective of this study was to evaluate the involvement of peripheral nitric oxide (NO) in vagotomy-induced pulmonary edema by verifying whether the nitric oxide synthases (NOS), constitutive (cNOS) and inducible (iNOS), participate in this mechanism. INTRODUCTION: It has been proposed that vagotomy induces neurogenic pulmonary edema or intensifies the edema of other etiologies. METHODS: Control and vagotomized rats were pretreated with 0.3 mg/kg, 3.0 mg/kg or 39.0 mg/kg of L-NAME, or with 5.0 mg/kg, 10.0 mg/kg or 20.0 mg/kg of aminoguanidine. All animals were observed for 120 minutes. After the animals' death, the trachea was catheterized in order to observe tracheal fluid and to classify the severity of pulmonary edema. The lungs were removed and weighed to evaluate pulmonary weight gain and edema index. RESULTS: Vagotomy promoted pulmonary edema as edema was significantly higher than in the control. This effect was modified by treatment with L-NAME. The highest dose, 39.0 mg/kg, reduced the edema and prolonged the survival of the animals, while at the lowest dose, 0.3 mg/kg, the edema and reduced survival rates were maintained. Aminoguanidine, regardless of the dose inhibited the development of the edema. Its effect was similar to that observed when the highest dose of L-NAME was administered. It may be that the non-selective blockade of cNOS by the highest dose of L-NAME also inhibited the iNOS pathway. CONCLUSION: Our data suggest that iNOS could be directly involved in pulmonary edema induced by vagotomy and cNOS appears to participate as a protector mechanism.

Role of the rostral ventrolateral medulla in the arterial hypertension in chronic renal failure.

Sympathetic activation in chronic renal failure (CRF) is a major mechanism leading to the progression of renal disease and hypertension. In the present study, we tested the hypothesis that in CRF increased reactive oxygen species (ROS) production in the RVLM mediated by enhanced circulating Angiotensin II (Ang II) is an important mechanism leading to hypertension in CRF. In CRF rats we found an increase in the abundance of p47(phox) and gp91(phox) mRNA within the RVLM associated with a reduction of Ang II type 1 receptors (AT(1)) mRNA in the brainstem compared to controls (C). Tempol but not candesartan into the RVLM decreased MAP in CRF but not in C rats. GABA into the RVLM decreased MAP in CRF (63 ± 8 mmHg) more intensely than in C (33 ± 3 mmHg). The results suggest that increased oxidative stress within the RVLM has an important participation to maintain hypertension in CRF rats apparently independently of AT(1) Ang II receptors.

The role of oxidative stress in renovascular hypertension.

1. There is mounting evidence that increased oxidative stress and sympathetic nerve activity play important roles in renovascular hypertension. In the present review, we focus on the importance of oxidative stress in two distinct populations of neurons involved with cardiovascular regulation: those of the rostral ventrolateral medulla (RVLM) and those of the paraventricular nucleus of the hypothalamus (PVN) in the maintenance of sympathoexcitation and hypertension in two kidney-one clip (2K1C) hypertensive rats. Furthermore, the role of oxidative stress in the clipped kidney is also discussed. 2. In the studies reviewed in this article, it was found that hypertension and renal sympathoexcitation in 2K1C rats were associated with an increase in Angiotensin II type one receptor (AT(1) ) expression and in oxidative markers within the RVLM, PVN and in the clipped kidneys of 2K1C rats. Furthermore, acute or chronic anti-oxidant treatment decreased blood pressure and sympathetic activity, and improved the baroreflex control of heart rate and renal sympathetic nerve activity in 2K1C rats. Tempol or vitamin C administration in the RVLM, PVN or systemically all reduced blood pressure and renal sympathetic activity. Cardiovascular improvement in response to chronic anti-oxidant treatment was associated with a downregulation of AT(1) receptors, as well as oxidative markers in the central nuclei and clipped kidney. 3. The data discussed in the present review support the idea that an increase in oxidative stress within the RVLM, PVN and in the ischaemic kidney plays a major role in the maintenance of sympathoexcitation and hypertension in 2K1C rats.

Involvement of nitric oxide pathways in neurogenic pulmonary edema induced by vagotomy

OBJECTIVE: The objective of this study was to evaluate the involvement of peripheral nitric oxide (NO) in vagotomy-induced pulmonary edema by verifying whether the nitric oxide synthases (NOS), constitutive (cNOS) and inducible (iNOS), participate in this mechanism. INTRODUCTION: It has been proposed that vagotomy induces neurogenic pulmonary edema or intensifies the edema of other etiologies. METHODS: Control and vagotomized rats were pretreated with 0.3 mg/kg, 3.0 mg/kg or 39.0 mg/kg of L-NAME, or with 5.0 mg/kg, 10.0 mg/kg or 20.0 mg/kg of aminoguanidine. All animals were observed for 120 minutes. After the animals' death, the trachea was catheterized in order to observe tracheal fluid and to classify the severity of pulmonary edema. The lungs were removed and weighed to evaluate pulmonary weight gain and edema index. RESULTS: Vagotomy promoted pulmonary edema as edema was significantly higher than in the control. This effect was modified by treatment with L-NAME. The highest dose, 39.0 mg/kg, reduced the edema and prolonged the survival of the animals, while at the lowest dose, 0.3 mg/kg, the edema and reduced survival rates were maintained. Aminoguanidine, regardless of the dose inhibited the development of the edema. Its effect was similar to that observed when the highest dose of L-NAME was administered. It may be that the non-selective blockade of cNOS by the highest dose of L-NAME also inhibited the iNOS pathway. CONCLUSION: Our data suggest that iNOS could be directly involved in pulmonary edema induced by vagotomy and cNOS appears to participate as a protector mechanism.

Upregulation of AT1R and iNOS in the rostral ventrolateral medulla (RVLM) is essential for the sympathetic hyperactivity and hypertension in the 2K-1C Wistar rat model.

BACKGROUND: We hypothesized that upregulation of angiotensin type 1 receptor (AT(1)R) and inducible nitric oxide (NO) synthase (iNOS) within the rostral ventrolateral medulla (RVLM) could contribute to two-kidney, one-clip (2K-1C) hypertension. METHODS: The experiments were performed in male Wistar rats, 6 weeks after the renal surgery. The animals were divided into control (SHAM, n = 18) and hypertensive groups (2K-1C, n = 18). Bilateral tissue punches were taken from sections containing the RVLM to perform iNOS gene expression analyses by the real-time PCR technique, and AT(1)R and iNOS protein expression analyses by western blotting. In addition, we injected losartan (1 nmol), an AT(1)R antagonist, and aminoguanidine (250 pmol), an iNOS inhibitor, bilaterally into the RVLM to analyze the mean arterial pressure (MAP) and renal sympathetic nerve activity (rSNA). RESULTS: iNOS mRNA expression levels were greater (P < 0.05) in the 2K-1C group compared to the SHAM group. Furthermore, the AT(1)R and iNOS protein expression were significantly increased in the RVLM of 2K-1C rats compared to SHAM rats. Injection of losartan into the RVLM reduced the MAP (11%) and rSNA (18%) only in the 2K-1C rats, whereas injection of aminoguanidine in the same region decreased the MAP (31%) and rSNA (34%) in hypertensive rats. CONCLUSIONS: The present study suggests that upregulation of AT(1)R and iNOS in the RVLM is important in the maintenance of high blood pressure and renal sympathetic activation in 2K-1C hypertension.

High sucrose intake in rats is associated with increased ACE2 and angiotensin-(1-7) levels in the adipose tissue.

Sucrose-fed rats, a model of metabolic syndrome, are characterized by insulin resistance, obesity, hypertension, and high plasma levels of triacylglycerols and angiotensin II (Ang II). However, whether tissue renin-angiotensin system (RAS) is altered in metabolic syndrome is unclear. To study this issue, food ad libitum and water (C) or 20% sucrose solution (SC) were given to adult male Wistar rats, for 30 days. Body weight (BW), blood pressure (BP), epididymal adipose tissue (EPI) mass, rate of in vivo fatty acid (FA) synthesis in EPI, circulating glucose, insulin, leptin, angiotensins I and II, triacylglycerols, and plasma renin (PRA) and angiotensin-converting enzyme (ACE) activities were evaluated. In kidneys and EPI, gene and protein expression of type 1 (AT(1)) and 2 (AT(2)) Ang II receptors, ACE, angiotensinogen (AGT) as well as protein expression of angiotensin-converting enzyme 2 (ACE2) were determined. In both tissues, Ang I, Ang II and Ang-(1-7) contents were also measured by HPLC. In SC rats higher BP, EPI mass, circulating triacylglycerols, insulin, leptin, PRA and, Ang II were found. In EPI, the rate of in vivo FA synthesis was associated with increased Ang-(1-7), protein expression of AT(1) and AT(2) receptors, ACE2, AGT, and gene expression of AGT although a reduction in ACE activity and in adipose Ang I and Ang II contents was observed. In kidneys, AT(1) and AT(2), ACE and AGT gene and protein expression as well as protein expression of ACE2 were unaltered while Ang II, Ang-(1-7) and ACE activity increased. These RAS component changes seem to be tissue specific and possibly are related to enhancement of FA synthesis, EPI mass and hypertension.

Chronic antioxidant treatment improves arterial renovascular hypertension and oxidative stress markers in the kidney in Wistar rats.

BACKGROUND: Sympathetic vasomotor hyperactivity and baroreflex dysfunction are involved in the development and maintenance of renovascular arterial hypertension. We hypothesized that angiotensin (Ang) II-dependent oxidative stress contributes to the pathophysiology of the two-kidney, one-clip (2K-1C) model. METHODS: The mean arterial pressure (MAP), baroreflex, and renal sympathetic nerve activity (rSNA) were evaluated after chronic administration of an antioxidant, vitamin C (vitC 150 mg/kg/day) in male Wistar 2K-1C rats. Additionally, the mRNA levels of Ang II subtype 1 receptor (AT(1)R), NAD(P)H oxidase subunits (p47phox and gp91phox), and major antioxidant enzymes were evaluated in the renal cortex. RESULTS: After vitC treatment, the MAP (170 +/- 4 vs. 133 +/- 6 mm Hg; P < 0.05) and rSNA (161 +/- 5 vs. 118 +/- 12 spikes/s; P < 0.05) were significantly reduced only in the 2K-1C group. VitC improved the baroreflex control of heart rate (HR) and rSNA. The expression of AT(1)R, p47phox, and gp91phox was elevated (51, 184, and 132%, respectively) in the clipped kidney of 2K-1C group. VitC downregulated AT(1)R in the clipped kidney (31%). Catalase (CAT) expression was reduced in clipped (70%) and nonclipped (83%) kidneys of 2K-1C rats. VitC treatment augmented the expression of glutathione peroxidase (GPx) in both clipped (185%) and nonclipped (212%) kidneys of the 2K-1C group. CONCLUSIONS: The present study suggests a role for oxidative stress in the cardiovascular and sympathetic alterations in renovascular hypertension, associated with changes in the expression of AT(1)R, NAD(P)H oxidase subunits, and antioxidant enzymes in the kidney.

Oxidative stress in the sympathetic premotor neurons contributes to sympathetic activation in renovascular hypertension.

BACKGROUND: Based on previous data, we hypothesized that an increase of angiotensin II (Ang II)-via the Ang II type 1 (AT-1) receptor-in the rostral ventrolateral medulla (RVLM) and the paraventricular nucleus (PVN) of the hypothalamus could activate NAD(P)H oxidase that will produce superoxides resulting in increased sympathetic activity and hypertension. METHODS: The mRNA expression of AT-1 receptors, NAD(P)H oxidase subunits (p47phox and gp91phox), and CuZnSOD were analyzed in the RVLM and PVN of male Wistar rats (Goldblatt hypertension model, 2K-1C). In addition, we administered Tempol 1 and 5 nmol into the RVLM, PVN, or systemically. The mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) were analyzed. RESULTS: The AT-1 mRNA expression and NAD(P)H oxidase subunits was greater in the RVLM and PVN in 2K-1C compared to the control group. Furthermore, the CuZnSOD expression was similar in both groups. Tempol 1 nmol into the RVLM reduced MAP (15 +/- 1%) and RSNA (11 +/- 2%) only in 2K-1C rats. Tempol (5 nmol) in the same region decreased the MAP (12 +/- 4%) and RSNA (20 +/- 7%), respectively, only in 2K-1C. In the PVN, Tempol 5 nmol resulted in a significant fall in the MAP (24 +/- 1%) and in the RSNA (7.9 +/- 2%) only in the 2K-1C. Acute intravenous (IV) infusion of Tempol decreased MAP and RSNA in the 2K-1C but not in the control rats. CONCLUSIONS: The data suggest that the hypertension and sympathoexcitation in 2K-1C rats were associated with an increase in oxidative stress within the RVLM, the PVN and systemically.

Oxidative stress contributes to renovascular hypertension.

BACKGROUND: Oxidative stress is a state in which excess reactive oxygen species (ROS) overwhelm endogenous antioxidant systems. It is known that this state has been involved in the development of hypertension. On the basis of previous data, we hypothesized that overactivity of NAD(P)H oxidase-derived ROS and the lowered activity of CuZnSOD, an endogenous antioxidant within the rostral ventrolateral medulla (RVLM), could contribute to 2K-1C (two-kidney one-clip) hypertension. Moreover, to test the functional significance of whether oxidative stress was involved in the maintenance of sympathetic vasomotor tone and blood pressure in 2K-1C hypertension, we administered Ascorbic Acid (Vit C), an antioxidant, into the RVLM or systemically. METHODS: Experiments were performed in male Wistar rats (6 weeks after renal surgery--Goldblatt hypertension model--2K-1C). The mRNA expression of NAD(P)H oxidase subunits (p47phox and gp91phox) and CuZnSOD were analyzed in the RVLM using real-time PCR technique. The mean arterial blood pressure, heart rate, and renal sympathetic nerve activity were analyzed. Blood samples were collected and measured using thiobarbituric acid-reactive substances (TBARS). RESULTS: The mRNA expression of NAD(P)H oxidase subnits (p47phox and gp91pox) was greater in 2K-1C compared to the control group in the RVLM, and CuZnSOD expression was similar in both groups. In the RVLM, Vit C resulted in a fall in arterial pressure and in the sympathetic activity only in the 2K-1C rats. Thiobarbituric acid-reactive substances (TBARS) were significantly greater in 2K-1C rats and the acute infusion of Vit C significantly decreased arterial pressure and renal sympathetic activity in 2K-1C. CONCLUSIONS: The results support the idea that an increase in oxidative stress within the RVLM and systemically plays a major role in maintaining high arterial blood pressure and sympathetic drive in 2K-1C hypertension.

Mecanismos fisiológicos e fisiopatológicos determinantes da atividade vasomotor simpática / Physiological and pathophysiological mechanisms determining the sympathetic vasomotor tone

RESUMO: A atividade vasomotora simpática é um dos determinantes da pressão arterial (PA). Estabelecer quais são os mecanismos geradores dessa atividade é importante para o entendimento de como o sistema cardiovascular opera, tanto em situações fisiológicas como fisiopatológicas. Os principais grupos pré-motores do simpático estão confinados no núcleo paraventricular do hipotálamo (PVN) e região rostoventrolateral bulbar (RVLM). Em diversas situações fisiopatológicas há aumento na atividade vasomotora simpática, em parte conseqüente a maior atividade dos neurônios do PVN e RVLM. Nesta breve revisão, foram discutidos os principais mecanismos de ativação simpática em diferentes modelos experimentais: 1) hipertensão renovascular, 2) hipertensão por baixa massa renal, 3) insuficiência cardíaca, 4) hipertensão por bloqueio do óxido nítrico, 5) obesidade e 6) dimorfismo sexual. As ações de diferentes mediadores sobre o PVN e RVLM podem em longo prazo determinar novos patamares de atividade simpática, modificando os níveis tensionais e dessa forma, contribuir para a progressão da doença cardiovascular.