Renal actions of atrial natriuretic peptide in spontaneously hypertensive rats: the role of nitric oxide as a key mediator

Atrial natriuretic peptide (ANP) is an important regulator of blood pressure (BP). One of the mechanisms whereby ANP impacts BP is by stimulation of nitric oxide (NO) production in different tissues involved in BP control. We hypothesized that ANP-stimulated NO is impaired in the kidneys of spontaneously hypertensive rats (SHR) and this contributes to the development and/or maintenance of high levels of BP. We investigated the effects of ANP on the NO system in SHR, studying the changes in renal nitric oxide synthase (NOS) activity and expression in response to peptide infusion, the signaling pathways implicated in the signaling cascade that activates NOS, and identifying the natriuretic peptide receptors (NPR), guanylyl cyclase receptors (NPR-A and NPR-B) and/or NPR-C, and NOS isoforms involved. In vivo, SHR and Wistar-Kyoto rats (WKY) were infused with saline (0.05 ml/min) or ANP (0.2 μg·kg(-1)·min(-1)). NOS activity and endothelial (eNOS), neuronal (nNOS), and inducible (iNOS) NOS expression were measured in the renal cortex and medulla. In vitro, ANP-induced renal NOS activity was determined in the presence of iNOS and nNOS inhibitors, NPR-A/B blockers, guanine nucleotide-regulatory (G(i)) protein, and calmodulin inhibitors. Renal NOS activity was higher in SHR than in WKY. ANP increased NOS activity, but activation was lower in SHR than in WKY. ANP had no effect on expression of NOS isoforms. ANP-induced NOS activity was not modified by iNOS and nNOS inhibitors. NPR-A/B blockade blunted NOS stimulation via ANP in kidney. The renal NOS response to ANP was reduced by G(i) protein and calmodulin inhibitors. We conclude that ANP interacts with NPR-C, activating Ca-calmodulin eNOS through G(i) protein. NOS activation also involves NPR-A/B. The NOS response to ANP was diminished in kidneys of SHR. The impaired NO system response to ANP in SHR participates in the maintenance of high blood pressure.     

Effects of aging and AT-1 receptor blockade on NO synthase expression and renal function in SHR

In an earlier study, we found increased NO production and NO synthase (NOS) expression in renal and vascular tissues of prehypertensive and adult spontaneously hypertensive rats (SHR). This study was designed to determine the effects of aging and AT-1 receptor blockade (losartan 30 mg/kg/day beginning at 8 weeks of age) on NO system in this model. Compared to the Wistar Kyoto (WKY) control rats, untreated SHR showed severe hypertension, elevated urinary NO metabolite (NO(chi)) excretion, marked upregulations of renal and vascular eNOS and iNOS proteins, normal renal function and heart weight at 9 weeks of age. Hypertension control with either AT-1 receptor or calcium channel blockade (felodipine 5 mg/kg/day) mitigated upregulation of NOS isoforms in the young SHR. With advanced age (63 weeks), the untreated SHR showed increased proteinuria, renal insufficiency, cardiomegaly, reduced urinary NO(chi) excretion and depressed renal and vascular NOS protein expressions as compared to the corresponding WKY group. AT-1 receptor blockade prevented proteinuria, renal insufficiency, cardiomegaly, and renal and vascular NOS deficiency. Thus, in young SHR, hypertension results in compensatory upregulation of renal and vascular NOS, which can be attenuated by vigorous antihypertensive therapy. With advanced age, untreated SHR exhibit cardiomegaly, renal dysfunction and marked reductions of eNOS and iNOS compared with the aged WKY rats. Hypertension control with AT-1 receptor blockade initiated early in the course of the disease prevents target organ damage and preserves renal and vascular NOS.     

The participation of brain NO synthase in blood pressure control of adult spontaneously hypertensive rats

Increased blood pressure (BP) in genetic hypertension is usually caused by high activity of sympathetic nervous system (SNS) which is enhanced by central angiotensin II but lowered by central nitric oxide (NO). We have therefore evaluated NO synthase (NOS) activity as well as neuronal NOS (nNOS), inducible NOS (iNOS) and endothelial NOS (eNOS) protein expression in brainstem and midbrain of adult spontaneously hypertensive rats (SHR) characterized by enhanced sympathetic vasoconstriction. We also studied possible participation of brain NO in antihypertensive effects of chronic captopril treatment of adult SHR. NOS activity was increased in midbrain of SHR compared to Wistar-Kyoto (WKY) rats. This could be ascribed to enhanced iNOS expression, whereas nNOS expression was unchanged and eNOS expression was reduced in this brain region. In contrast, no significant changes of NOS activity were found in brainstem of SHR in which nNOS and iNOS expression was unchanged, but eNOS expression was increased. Chronic captopril administration lowered BP of adult SHR mainly by attenuation of sympathetic tone, whereas the reduction of angiotensin II-dependent vasoconstriction and the decrease of residual BP (amelioration of structural remodeling of resistance vessels) were less important. This treatment did not affect significantly either NOS activity or expression of any NOS isoform in the two brain regions. Our data do not support the hypothesis that altered brain NO formation contributes to sympathetic hyperactivity and high BP of adult SHR with established hypertension.     

Effect of apocynin treatment on renal expression of COX-2, NOS1, and renin in Wistar-Kyoto and spontaneously hypertensive rats

Macula densa (MD) cells of the juxtaglomerular apparatus (JGA) synthesize type 1 nitric oxide synthase (NOS1) and type 2 cyclooxygenase (COX-2). Both nitric oxide (NO) and prostaglandins have been considered to mediate or modulate the control of renin secretion. Reactive oxygen species (ROS) produced locally by NADPH oxidase may influence NO bioavailability. We have tested the hypothesis that in hypertension elevated ROS levels may modify the expression of NOS1 and COX-2 in the JGA, thereby interacting with juxtaglomerular signaling. To this end, spontaneously hypertensive rats (SHR) and Wistar-Kyoto control rats (WKY) received the specific NADPH oxidase inhibitor, apocynin, during 3 wk. Renal functional and histochemical parameters, plasma renin activity (PRA), and as a measure of ROS activity, urinary isoprostane excretion (IP) were evaluated. Compared with WKY, IP levels in untreated SHR were 2.2-fold increased, and NOS1 immunoreactiviy (IR) of JGA 1.5-fold increased, whereas COX-2 IR was reduced to 35%, renin IR to 51%, and PRA to 7%. Apocynin treatment reduced IP levels in SHR to 52%, NOS1 IR to 69%, and renin IR to 62% of untreated SHR, whereas renin mRNA, COX-2 IR, glomerular filtration rate, PRA, and systolic blood pressure remained unchanged. WKY revealed no changes under apocynin treatment. These data show that NADPH oxidase is an important contributor to elevated levels of ROS in hypertension. Upregulation of MD NOS1 in SHR may have the potential of blunting the functional impact of ROS at the level of bioavailable NO. Downregulated COX-2 and renin levels in SHR are apparently unrelated to oxidative stress, since apocynin treatment had no effect on these parameters.     

Alterations of NO synthase isoforms in brain and kidney of rats with genetic and salt hypertension

Both brain and peripheral nitric oxide (NO) play a role in the control of blood pressure and circulatory homeostasis. Central NO production seems to counteract angiotensin II-induced enhancement of sympathetic tone. The aim of our study was to evaluate NO synthase (NOS) activity and protein expression of its three isoforms--neuronal (nNOS), endothelial NOS (eNOS) and inducible (iNOS)--in two brain regions involved in blood pressure control (diencephalon and brainstem) as well as in the kidney of young adult rats with either genetic (12-week-old SHR) or salt-induced hypertension (8-week-old Dahl rats). We have demonstrated reduced nNOS and iNOS expression in brainstem of both hypertensive models. In SHR this abnormality was accompanied by attenuated NOS activity and was corrected by chronic captopril treatment which prevented the development of genetic hypertension. In salt hypertensive Dahl rats nNOS and iNOS expression was also decreased in the diencephalon where neural structures important for salt hypertension development are located. As far as peripheral NOS activity and expression is concerned, renal eNOS expression was considerably reduced in both genetic and salt-induced hypertension. In conclusions, we disclosed similar changes of NO system in the brainstem (but not in the diencephalon) of rats with genetic and salt-induced hypertension. Decreased nNOS expression was associated with increased blood pressure due to enhanced sympathetic tone.     

Antihypertensive effect of low ethanol intake in spontaneously hypertensive rats

Light to moderate drinking in humans lowers the risk of coronary heart disease and may lower blood pressure. We examined the effect of chronic low daily alcohol consumption on blood pressure, platelet cytosolic free calcium [Ca²⁺]_i, tissue aldehyde conjugates and renal vascular changes in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). We also examined the effects of the same weekly amount of alcohol consumption over a one day period each week simulating weekend drinking in humans. Animals, age 7 weeks, were divided into six groups of six animals each and were treated as follows: WKY and SHR control, normal drinking water; WKY and SHR, 0.5% ethanol in drinking water; WKY and SHR, 3.5% ethanol in drinking water one day/week. After 14 weeks systolic blood pressure, platelet [Ca²⁺]_i, liver, kidney and aortic aldehyde conjugates were significantly higher (p < 0.05) in untreated SHRs as compared to untreated WKYs. Daily 0.5% ethanol consumption in SHRs significantly (p < 0.05) attenuated these changes and also attenuated smooth muscle cell hyperplasia and narrowing of the lumen in small arteries and arterioles of the kidney. WKY rats treated with 0.5% ethanol had lower aldehyde conjugates without any significant effect on blood pressure and platelet [Ca²⁺]_i as compared to WKY controls. Consumption of 3.5% ethanol one day/week did not affect blood pressure and associated changes in normotensive WKY rats or hypertensive SHRs as compared to their respective controls. These results suggest that chronic daily low ethanol intake lowers blood pressure in SHRs by lowering tissue aldehyde conjugates and cytosolic free calcium.     

Indapamide-induced prevention of myocardial fibrosis in spontaneous hypertension rats is not nitric oxide-related

We studied the effect of thiazide-like diuretic--indapamide on fibrosis development in the left ventricle of young spontaneously hypertensive rats (SHR) and assessed the involvement of nitric oxide in this process. Six-week-old male SHR were treated with indapamide (1 mg/kg/day) for six weeks. Age-matched SHR were used as hypertensive and Wistar-Kyoto rats (WKY) as normotensive control. Systolic blood pressure was measured by tail-cuff plethysmography. Nitric oxide synthase (NOS) activity, protein expressions of endothelial (eNOS) and inducible NOS (iNOS), myocardial fibrosis and collagen type I and III were determined in the left ventricle. Indapamide treatment partially prevented SBP increase in SHR (SHR+Indapamide: 157+/-4, SHR: 171+/-3, WKY: 119+/-3 mmHg). Indapamide prevented myocardial fibrosis development in SHR, but without affecting collagen type I to type III ratio. Indapamide did not affect NOS activity as well as eNOS and iNOS protein expressions in the left ventricles evaluated by both Western blot and immunohistochemically. In conclusion, our results indicate that indapamide-induced prevention of myocardial fibrosis is not mediated by nitric oxide-related mechanism.     

Apocynin attenuates oxidative stress and hypertension in young spontaneously hypertensive rats independent of ADMA/NO pathway

Both NADPH oxidase-derived reactive oxygen species (ROS) and asymmetric dimethylarginine (ADMA) are increased in hypertension. Apocynin, an NADPH oxidase inhibitor, could inhibit ROS, thus we tested whether apocynin can block NADPH oxidase and prevent increases of ADMA and blood pressure (BP) in spontaneously hypertensive rats (SHRs). SHRs and Wistar Kyoto (WKY) rats, aged 4 weeks, were assigned to four groups: untreated SHRs and WKY rats, SHRs and WKY rats that received 2.5 mM apocynin for 8 weeks. BP was significantly higher in SHRs compared to WKY rats, which was attenuated by apocynin. Apocynin prevented p47phox translocation in SHR kidneys, but not the increase of superoxide and H(2)O(2). Additionally, apocynin did not protect SHRs against increased ADMA. Apocynin blocks NADPH oxidase to attenuate hypertension, but has little effect on the ADMA/nitric oxide (NO) pathway in young SHRs. The reduction of ROS and the preservation of NO simultaneously might be a better approach to restoring ROS-NO balance to prevent hypertension.     

Chronic administration of adrenomedullin attenuates the hypertension and increases renal nitric oxide synthase in Dahl salt-sensitive rats

Adrenomedullin reduces systemic blood pressure and increases urinary sodium excretion partly through the release of nitric oxide. We hypothesized that chronic adrenomedullin infusion ameliorates salt-sensitive hypertension and increases the expression of renal nitric oxide synthase (NOS) in Dahl salt-sensitive (DS) rats, because the reduced renal NOS expression promotes salt sensitivity. DS rats and Dahl salt-resistant (DR) rats were fed a high sodium diet (8.0% NaCl) for 3 weeks. The high sodium diet resulted in an increase in blood pressure and a reduction of urinary sodium excretion in association with increased renal adrenomedullin concentrations and decreased expression of renal neuronal NOS (nNOS) and renal medullary endothelial NOS (eNOS) in DS rats compared with DR rats. Chronic adrenomedullin infusion partly inhibited the increase of blood pressure and proteinuria in association with a restoration of renal nNOS and medullary eNOS expression in DS rats under the high sodium diet. The immunohistochemical analysis revealed that the restored renal nNOS expression induced by chronic adrenomedullin infusion may reflect the restoration of nNOS expression in the macula densa and inner medullary collecting duct. These results suggest that adrenomedullin infusion has beneficial effects on this hypertension probably in part through restored renal NOS expression in DS rats.     

Nitric oxide synthase activity in blood vessels of spontaneously hypertensive rats: antioxidant protection by gamma-tocotrienol.

Involvement of free radicals and nitric oxide (NO) has long been implicated to the pathogenesis of essential hypertension. Several studies using antioxidants as the radical scavenger have shown to confer protection against free radical mediated diseases. This study is designed to investigate the role of antioxidant gamma-tocotrienol on endothelial nitric oxide synthase (NOS) activity in spontaneously hypertensive rats (SHR). SHR's were divided into four groups namely untreated SHR (HC), treatment with 15 mg gamma-tocotrienol/kg diet (gammal), 30 mg gamma-tocotrienol/kg diet (gamma2) and 150 mg gamma-tocotrienol/kg diet (gamma3) and studied for three months. Wister Kyoto (WKY) rats were used as the control (C). Blood pressure was recorded every fortnightly by tail plethysmography. Animals were sacrificed and NOS activity in blood vessels was measured by [3H]arginine radioactive assay. Nitrite concentration in plasma was determined by Greis assay and lipid peroxides in the blood vessels by spectrofluorometry. This study showed that gamma-tocotrienol significantly reduced systolic blood pressure (SBP) in SHRs with a maximum reduction in group treated with gamma-tocotrienol 15 mg/kg diet (HC: 210 +/- 9 mmHg, gammal:123 +/- 19 mmHg). Blood vessels from untreated SHR showed a reduced NOS activity compare to that of WKY rats (C: 1.54 +/- 0.26 pmol/mg protein, HC: 0.87 +/- 0.23 pmol/mg protein; p<0.001). Gamma-tocotrienol improves NOS activity in all the groups with more significance in group gamma2 (p<0.001) and gamma3 (p<0.05). Plasma level of nitrite was reduced in SHR from 55 +/- 3 microM/ml in WKY to 26+/-2 muM/ml (p<0.001). Plasma nitrite level was reversed by treatment with gamma-tocotrienol. (gammal: p<0.001, gamma2: p<0.005, gamma3: p<0.001, respectively). In all the treatment groups, NOS activity showed significant negative correlation with blood pressure (gammal: r=-0.716, p<0.05; gamma2: r=-0.709, p<0.05; gamma3: r=-0.789, p<0.05). For plasma nitrite, although it shows a negative correlation with blood pressure it was significant only in gammal (r=-0.676, p<0.05) and gamma2 (r=-0.721, p<0.05). From this study we found that compared to WKY rats, SHR has lower NOS activity in blood vessels, which upon treatment with antioxidant gamma-tocotrienol increased the NO activity and concomitantly reduced the blood pressure. These findings further strengthen the hypothesis that free radicals and NO play critical role in pathogenesis of essential hypertension.     

Effect of Silodosin,an Alpha1A-Adrenoceptor Antagonist,on Ventral Prostatic Hyperplasia in the Spontaneously Hypertensive Rat

Background

A decreased prostatic blood flow could be one of the risk factors for benign prostatic hyperplasia/benign prostatic enlargement. The spontaneously hypertensive rat (SHR) shows a chronic prostatic ischemia and hyperplastic morphological abnormalities in the ventral prostate. The effect of silodosin, a selective alpha_1A-adrenoceptor antagonist, was investigated in the SHR prostate as a prostatic hyperplasia model focusing on prostatic blood flow.

Methods

Twelve-week-old male SHRs were administered perorally with silodosin (100 μg/kg/day) or vehicle once daily for 6 weeks. Wistar Kyoto (WKY) rats were used as normotensive controls and were treated with the vehicle. The effect of silodosin on blood pressure and prostatic blood flow were estimated and then the prostates were removed and weighed. The tissue levels of malondialdehyde (MDA), interleukin-6 (IL-6), chemokine (C-X-C motif) ligand 1/cytokine-induced neutrophil chemoattractant 1 (CXCL1/CINC1), tumor necrosis factor-alpha (TNF-α), transforming growth factor beta 1 (TGF-β1), basic fibroblast growth factor (bFGF) and alpha-smooth muscle actin (α-SMA) were measured. The histological evaluation was also performed by hematoxylin and eosin staining.

Results

There was a significant increase in blood pressure, prostate weight, prostate body weight ratio (PBR), tissue levels of MDA, IL-6, CXCL1/CINC1, TNF-α, TGF-β1, bFGF and α-SMA in the SHR compared to the WKY rat. The ventral prostate in the SHR showed the morphological abnormalities compared to the WKY rat. Prostatic blood flow was decreased in the SHR. However, treatment with silodosin significantly restored the decreased prostatic blood flow in the SHR. Moreover, silodosin normalized tissue levels of MDA, IL-6, CXCL1/CINC1, TNF-α, TGF-β1, bFGF and α-SMA, and it ameliorated ventral prostatic hyperplasia in the SHR excluding blood pressure. Silodosin decreased PBR but not prostate weight in the SHR.

Conclusions

Silodosin can inhibit the progression of prostatic hyperplasia through a recovery of prostatic blood flow.     

Spontaneously hypertensive and Wistar Kyoto rats are genetically disparate.

Spontaneously hypertensive rats (SHR) are one of the most common animal models used to study essential hypertension in humans. Because SHR and normotensive Wistar Kyoto (WKY) rats were both established from the same parental, normotensive Wistar stock, WKY animals have been used almost exclusively as control animals in studies of SHR. Recently, the suitability of WKY rats as normotensive controls for SHR has been challenged. To establish whether or not SHR and WKY rats share the same immunologic backgrounds, we initially performed a series of skin grafting experiments on these animals. In all cases, grafts of SHR donor skin to WKY recipients and of WKY donor skin to SHR recipients resulted in complete rejection within 7 to 10 days. In addition, grafts of WKY donor skin to other WKY recipients resulted in graft rejection. By contrast, skin grafts between SHRs were always accepted. To further characterize the genetic distinctions between SHR and WKY rats, allelic profiles based on a series of immunologic and biochemical markers were established for each strain. These findings clearly establish that SHR and WKY rats differ at the major histocompatibility complex, in specific blood group antigens, and in a panel of isozymic markers. Moreover, whereas SHRs have the same genetic profiles irrespective of source, some colonies of WKY rats are outbred, as judged by their variant allelic profiles.     

eNOS involved in colitis-induced mucosal blood flow increase

The role of NO in inflammatory bowel disease is controversial. Studies indicate that endothelial nitric oxide synthase (eNOS) might be involved in protecting the mucosa against colonic inflammation. The aim of this study was to investigate the involvement of nitric oxide (NO) in regulating colonic mucosal blood flow in two different colitis models in rats. In anesthetized control and colitic rats, the distal colon was exteriorized and the mucosa visualized. Blood flow (laser-Doppler flowmetry) and arterial blood pressure were continuously monitored throughout the experiments, and vascular resistance was calculated. Trinitrobenzene sulfonic acid (TNBS) or dextran sulfate sodium (DSS) was used to induce colitis. All groups were given the NOS inhibitor N(omega)-nitro-l-arginine (l-NNA) or the inducible NOS (iNOS) inhibitor l-N(6)-(1-iminoethyl)-lysine (l-NIL). iNOS, eNOS, and neuronal NOS (nNOS) mRNA in colonic samples were investigated with real-time RT-PCR. Before NOS inhibition, colonic mucosal blood flow, expressed as perfusion units, was higher in both colitis models compared with the controls. The blood flow was reduced in the TNBS- and DSS-treated rats during l-NNA administration but was not altered in the control group. Vascular resistance increased more in the TNBS- and DSS-treated rats than in the control rats, indicating a higher level of vasodilating NO in the colitis models. l-NIL did not alter blood pressure or blood flow in any of the groups. iNOS and eNOS mRNA increased in both colitis models, whereas nNOS remained at the control level. TNBS- and DSS-induced colitis results in increased colonic mucosal blood flow, most probably due to increased eNOS activity.     

CLOCK/BMAL1 regulates human nocturnin transcription through binding to the E-box of nocturnin promoter

We attempted to clarify the effects of cyclohexenonic long-chain fatty alcohol (N-hexacosanol) on nitric oxide synthase (NOS) in streptozotocin-induced diabetic nephropathy. After induction of experimental diabetes with streptozotocin, rats were maintained for 8 weeks with or without treatment by N-hexacosanol (8 mg/kg i.p. every day). Urinary albumin excretion, blood chemistry, immunoblot analysis, and real-time polymerase chain reactions (real-time PCR) of endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS) were investigated. Although N-hexacosanol had no effects on serum glucose or insulin level, it normalized serum creatinine and urinary albumin excretion. N-hexacosanol was found to improve the diabetes-induced alterations in the eNOS, iNOS, and nNOS protein and their mRNA levels. Histologically, N-hexacosanol inhibited the progression to glomerular sclerosis. Our data suggest that N-hexacosanol improves diabetes-induced NOS alterations in the kidney, resulting in the amelioration of diabetic nephropathy.     

Discoordinate regulation of renal nitric oxide synthase isoforms in ovariectomized mRen2. Lewis rats

Estrogen depletion markedly exacerbates hypertension in female congenic mRen2. Lewis rats, a model of tissue renin overexpression. Because estrogen influences nitric oxide synthase (NOS) and NO may exert differential effects on blood pressure, the present study investigated the functional expression of NOS isoforms in the kidney of ovariectomized (OVX) mRen2. Lewis rats. OVX-mRen2. Lewis exhibited an increase in systolic blood pressure (SBP) of 171 +/- 5 vs. 141 +/- 7 mmHg (P < 0.01) for intact littermates. Renal cortical mRNA and protein levels for endothelial NOS (eNOS) were reduced 50-60% (P < 0.05) and negatively correlated with blood pressure. In contrast, cortical neuronal NOS (nNOS) mRNA and protein levels increased 100 to 300% (P < 0.05). In the OVX kidney, nNOS immunostaining was more evident in the macula densa, cortical tubules, and the medullary collecting ducts compared with the intact group. To determine whether the increase in renal nNOS expression constitutes a compensatory response to the reduction in renal eNOS, we treated both intact and OVX mRen2. Lewis rats with the selective nNOS inhibitor L-VNIO from 11 to 15 wk of age. The nNOS inhibitor reduced blood pressure in the OVX group (185 +/- 3 vs. 151 +/- 8 mmHg, P < 0.05), but pressure was not altered in the intact group (146 +/- 4 vs. 151 +/- 4 mmHg). In summary, exacerbation of blood pressure in the OVX mRen2. Lewis rats was associated with the discoordinate regulation of renal NOS isoforms. Estrogen sensitivity in this congenic strain may involve the influence of NO through the regulation of both eNOS and nNOS.     

Magnolol Administration in Normotensive Young Spontaneously Hypertensive Rats Postpones the Development of Hypertension: Role of Increased PPAR Gamma,Reduced TRB3 and Resultant Alleviative Vascular Insulin Resistance

Patients with prehypertension are more likely to progress to manifest hypertension than those with optimal or normal blood pressure. However, the mechanisms underlying the development from prehypertension to hypertension still remain largely elusive and the drugs for antihypertensive treatment in prehypertension are absent. Here we determined the effects of magnolol (MAG) on blood pressure and aortic vasodilatation to insulin, and investigated the underlying mechanisms. Four-week-old male spontaneous hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto (WKY) control rats were used. Our results shown that treatment of young SHRs with MAG (100 mg/kg/day, o.g.) for 3 weeks decreased blood pressure, improved insulin-induced aorta vasodilation, restored Akt and eNOS activation stimulated by insulin, and increased PPARγ and decreased TRB3 expressions. In cultured human umbilical vein endothelial cells (HUVECs), MAG incubation increased PPARγ, decreased TRB3 expressions, and restored insulin-induced phosphorylated Akt and eNOS levels and NO production, which was blocked by both PPARγ antagonist and siRNA targeting PPARγ. Improved insulin signaling in HUVECs by MAG was abolished by upregulating TRB3 expression. In conclusion, treatment of young SHRs with MAG beginning at the prehypertensive stage decreases blood pressure via improving vascular insulin resistance that is at least partly attributable to upregulated PPARγ, downregulated TRB3 and consequently increased Akt and eNOS activations in blood vessels in SHRs.     

Control of oxidative stress in microcirculation of spontaneously hypertensive rats

One mechanism for organ damage in individuals with arterial hypertension may be due to oxygen free radical production. This study was designed to localize free radicals in a microvascular network of mature spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto (WKY) rats. Because glucocorticoids play a role in pressure elevation of SHRs, we investigated their role in microvascular free radical formation. Oxygen radical production in mesentery was detected by tetranitroblue tetrazolium reduction to formazan aided by digital light-absorption measurements. Formazan deposits were observed in the endothelial cells and lumens of all microvessels and in lymphatic endothelia but were fewer in tissue parenchyma. The formazan distribution in younger (14-16 wk old) WKY rats and SHRs was heterogeneous with low values in capillaries and small arterioles/venules (<30 microm) but enhanced deposits in larger venules. Adrenalectomy served to reduce the formazan density in SHRs to the level of WKY rats, whereas dexamethasone supplementation of the adrenalectomized rats caused elevation in the larger venules of SHRs. In older (40 wk old) SHRs, formazan levels were elevated in all hierarchies of microvessels. After pressure reduction was employed with chronic hydralazine treatment, the formazan deposits were reduced in all locations of the microcirculation in both WKY rats and SHRs. Elevated formazan deposits were also found in lymphatic endothelium. These results suggest that oxygen free radical production is elevated in both high- and low-pressure regions of SHR microcirculation via a process that is controlled by glucocorticoids. Older SHRs have higher formazan levels than younger SHRs in all microvessels. Chronic hydralazine treatment, which serves to reduce arterial blood pressure, attenuates tetranitroblue tetrazolium reduction in WKY rats and SHRs even in venules of the microcirculation, which has no micropressure elevation. Free radical production may be a more global condition in SHRs and may not be limited to arteries and arterioles.     

Upregulation of platelet (L)-arginine: nitric oxide pathway after exercise training in hypertension

We investigated whether physical exercise can affect platelet L-arginine?- nitric oxide pathway in spontaneously hypertensive rats (SHR). Sixteen male SHR and 16 Wistar Kyoto rats (WKY) were divided among exercise (EX) and sedentary (SED) groups. After 20?weeks of treadmill training, systolic blood pressure (mm?Hg) was significantly lower in exercised spontaneously hypertensive rats (SHR/EX; 138?± 8) than in sedentary spontaneously hypertensive rats (SHR/SED; 214?± 9). Exercise significantly increased platelet L-arginine transport (pmol L-arginine·(10(9) cells)(-1)·min(-1)), assessed by incubation with L-[(3)H]-arginine, in both WKY (SED, 0.196?± 0.054 compared with EX, 0.531?± 0.052) and SHR (SED, 0.346?± 0.076 compared with EX, 0.600?± 0.049). Nitric oxide synthase (NOS) activity (pmol L-citrulline·(10(8) cells)(-1)), measured by the conversion of L-[(3)H]-arginine to L-[(3)H]-citrulline, was significantly increased in SHR/EX (0.072?± 0.007) compared with SHR/SED (0.038?± 0.007), but no changes were observed in WKY. The iNOS and eNOS protein levels assessed by Western blot were not affected by exercise. This upregulation of the platelet L-arginine-NO pathway may attenuate the risk of thromboembolic events, supporting the role of exercise in hypertension management.