Vehicle-treated SHRSP Research Articles

Activation of microglia within paraventricular nucleus of hypothalamus is NOT involved in maintenance of established hypertension

BackgroundInflammation within paraventricular nucleus of the hypothalamus (PVN), a key circulatory control center in the hypothalamus, is an important pathology of sympathetic hyperactivity. Brain inflammation is mainly mediated by microglia, innate immune cells in the brain. Activated microglia produce inflammatory cytokines with alteration of their morphology. Increase in inflammatory cytokines synthesis coincides with activation of microglia within PVN of angiotensin II-induced hypertensive model and myocardial infarction-induced heart failure model. Although the increase in inflammatory cytokines and the microglial activation within PVN were also seen in spontaneously hypertensive rats (SHR), the model of essential hypertension, their involvement in blood pressure regulation has still be fully clarified. In the present study, we examined whether activated microglia within PVN were involved in maintenance of established severe hypertension with sympathoexcitation. MethodsMinocycline (25mg/kg/day), an inhibitor of microglial activation, or vehicle were orally administered to stroke-prone SHR (SHRSP) and normotensive Wistar-Kyoto (WKY) rats for 2 weeks from 15-weeks-old, the age of established hypertension. ResultsSystolic blood pressure was comparable between minocycline treated-SHRSP and vehicle treated-SHRSP, whereas morphological analysis of microglia revealed smaller cell size in minocycline treated-SHRSP than vehicle treated-SHRSP, implying that minocycline deactivated microglia within PVN. ConclusionsActivated microglia with morphological alteration within PVN are not involved in the maintenance of established severe hypertension, and inflammation within PVN could not be the therapeutic target of established hypertension.

Decreased proportion of Foxp3+ CD4+ regulatory T cells contributes to the development of hypertension in genetically hypertensive rats.

Dysregulation of the sympathetic nervous system and the immune system has been highlighted in the pathogenesis of hypertension. Foxp3 regulatory T (Treg) cells, which maintain immune homeostasis, have potent antihypertensive properties. We systematically explored whether Treg cells proportions are altered in stroke-prone spontaneously hypertensive rats (SHRSP) with increased sympathetic activity. Then, we focused on Treg cells in the spleen and determined whether Treg cells proportion in the spleen could be affected by splenic sympathetic input associated with the progression of hypertension. We also investigated effects of Treg cell induction on hypertension development and cardiac hypertrophy in SHRSP. We evaluated Treg cells in SHRSP. Compared with normotensive Wistar-Kyoto (WKY) rats, SHRSP exhibited decreased proportions of CD4CD25Foxp3 cells (Treg cells) in the spleen before the onset of hypertension. Splenic sympathetic denervation in prehypertensive SHRSP attenuated the reduction of Treg cells at 4 weeks after denervation (P < 0.05) and delayed the development of hypertension in SHRSP. Interleukin (IL)-2 and anti-IL-2 mAb complex selectively induced Treg cells in vivo (P < 0.01), delayed the development of hypertension and decreased the heart weight/body weight ratio (4.64 ± 0.06 vs. 4.25 ± 0.05 mg/g, P < 0.01) and the cross-sectional area of cardiac myocytes in SHRSP compared with vehicle-treated SHRSP (580 ± 3.91 vs. 438 ± 4.43 μm, P < 0.0001). Our findings indicate that a decrease in Treg cell proportion is crucial for the development of hypertension and cardiac hypertrophy in SHRSP, which is involved in sympathetic neural input to the spleen.

Pharmacological manipulation of arachidonic acid-epoxygenase results in divergent effects on renal damage.

Kidney damage is markedly accelerated by high-salt (HS) intake in stroke-prone spontaneously hypertensive rats (SHRSP). Epoxyeicosatrienoic acids (EETs) are epoxygenase products of arachidonic acid which possess vasodepressor, natriuretic, and anti-inflammatory activities. We examined whether up-regulation (clofibrate) or inhibition [N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH)] of epoxygenase would alter systolic blood pressure (SBP) and/or renal pathology in SHRSP on HS intake (1% NaCl drinking solution). Three weeks of treatment with clofibrate induced renal cortical protein expression of CYP2C23 and increased urinary excretion of EETs compared with vehicle-treated SHRSP. SBP and urinary protein excretion (UPE) were significantly lowered with clofibrate treatment. Kidneys from vehicle-treated SHRSP, which were on HS intake for 3 weeks, demonstrated focal lesions of vascular fibrinoid degeneration, which were markedly attenuated with clofibrate treatment. In contrast, 2 weeks of treatment with the selective epoxygenase inhibitor, MS-PPOH, increased UPE without significantly altering neither urinary EET levels nor SBP. Kidneys from vehicle-treated SHRSP, which were on HS intake for 11 days, demonstrated occasional mild damage whereas kidneys from MS-PPOH-treated rats exhibited widespread malignant nephrosclerosis. These results suggest that pharmacological manipulation of epoxygenase results in divergent effects on renal damage and that interventions to increase EET levels may provide therapeutic strategies for treating salt-sensitive hypertension and renal damage.

Abstract 241: Splenic T Regulatory Lymphocytes Are Reduced in Genetically Hypertensive Rats Associated with Central Sympathoexcitation

Background: Chronic inflammation plays a role in the pathogenesis of hypertension. Among the subsets of T lymphocytes, T regulatory lymphocytes (Tregs), which are immune suppressors of inflammatory responses, are reported to prevent angiotensin II (AngII)-induced hypertension and vascular injury. We hypothesized that Tregs play a critical role in the development and maintenance of hypertension. The aim of the present study was to determine whether Tregs are decreased in genetically hypertensive rats at both prehypertensive and established ages compared with those in normotensive rats, and if so, to examine whether blockade of brain AngII type 1 receptors (AT1R) affects Tregs in hypertensive rats. Methods and Results: We examined Tregs in stroke-prone spontaneously hypertensive rats (SHRSP) at prehypertensive (5 week old) and established ages (12 week old) and age-matched normotensive Wistar-Kyoto rats (WKY). In both SHRSP and WKY, the transcription factor forkhead box P3 (Foxp3) mRNA expression levels were greater in the spleen than in other organs. However, Foxp3 mRNA and protein expression levels in the spleen were significantly lower in SHRSP than in WKY (Foxp3 mRNA: 0.47±0.03 vs. 1.02±0.03, protein: 0.39±0.02 vs. 0.66±0.03, n=6 for each, p&lt;0.05). Flow cytometric analysis revealed that CD4+CD25+Foxp3+ cells (Tregs) in the spleen were significantly lower in SHRSP than in WKY (%Foxp3+ gated on CD4+CD25+ cells in the spleen; 45.4±1.4 vs. 58.1±2.0, n=3 for each, p&lt;0.05). In addition, CD4+CD25+Foxp3+ cells in the spleen were lower in prehypertensive SHRSP, but not in the thymus. In hypertensive SHRSP, intracerebroventricular infusion of AT1R blocker (losartan, 1mg/kg/day for 2 weeks) reduced blood pressure and 24-hour urinary norepinephrine excretion, and upregulated Foxp3 mRNA expression levels in the spleen (0.44±0.04 vs. 0.31±0.02, n=3-4, p&lt;0.05, vs. vehicle-treated SHRSP). Conclusion: Our findings indicate that splenic Tregs are reduced in SHRSP at both prehypertensive and established hypertensive stages. These alterations may contribute to the development and maintenance of hypertension. Central sympathoinhibition increases the reduced splenic Tregs in SHRSP suggesting interaction between sympathetic hyperactivity and Tregs.

Renoprotective mechanisms of telmisartan on renal injury and inflammation in SHRSP.Z-Leprfa/IzmDmcr rats

SHRSP.Z-Lepr(fa)/IzmDmcr (SHRSP fatty) rats create a new animal model of metabolic syndrome. However, the renoprotective effect of telmisartan therapy and its underlying mechanisms in SHRSP fatty rats remain unknown. We evaluate the effects of long-term telmisartan therapy on renal dysfunction, podocyte injury, inflammation, and transforming growth factor-β1 (TGF-β1)/Smad, epithelial-mesenchymal transition (EMT), mitogen-activated protein kinase (MAPK), Rho-kinase, and cell-cycle progression pathway in the renal cortex of SHRSP fatty rats. Seven-week-old male SHRSP fatty rats were treated with vehicle, telmisartan, and hydralazine for 8 weeks. Age-matched male Wistar-Kyoto/Izumo rats served as a control group. Vehicle-treated SHRSP fatty rats developed proteinuria and renal dysfunction, which in the telmisartan group was less than the vehicle and hydralazine group without changing blood pressure. Glomerulosclerosis and interstitial fibrosis were impaired in SHRSP fatty rats, and the renal damage in the telmisartan group was less than the vehicle and hydralazine groups. Decreased expression of nephrin and podocin and increased desmin-positive area in SHRSP fatty rats were restored by telmisartan but not hydralazine. TGF-β1/Smad, EMT marker, MAPK, Rho-kinase, and cell-cycle progression pathways were upregulated in SHRSP fatty rats, and these increased proteins in the telmisartan group were less than the vehicle and hydralazine group. Telmisartan administration resulted in significant suppression in tumor necrosis factor-α expression and nuclear factor-κB phosphorylation. Long-term telmisartan therapy may improve renal dysfunction, glomerulosclerosis, podocyte injury, and inflammation associated with EMT, TGF-β/Smad, MAPK, Rho-kinase pathway in SHRSP fatty rats. Thus, telmisartan may have significant therapeutic potential for metabolic syndrome.

Cilostazol alleviates cerebral small-vessel pathology and white-matter lesions in stroke-prone spontaneously hypertensive rats

Small-vessel pathology is believed to have a critical role in cerebrovascular white-matter (WM) lesions. However, the cellular aspect of vascular pathology, including the phenotypic modulation of smooth-muscle cells (SMCs) and its role in the small-vessel disease, remains undefined. The involvement or otherwise of the phenotypic modulation of SMCs in cerebral small-vessel pathology has been investigated, and the effect of cilostazol on both the small vessels and the WM lesions has been determined in stroke-prone spontaneously hypertensive rats (SHRSP). Male SHRSP and Wistar Kyoto rats were used. SHRSP were divided into two groups: the cilostazol-treated (20-week treatment) and vehicle-treated groups. Small-vessel pathology was analyzed using both histopathology and immunohistochemistry for smooth-muscle actin and nonmuscle myosin heavy chain (SMemb, a marker for the synthetic phenotype of SMC). The pathological changes in the WM were quantified in terms of the numerical density of activated microglia and the degree of WM lesions. Vascular wall thickening and perivascular fibrosis, determined by the wall area/lumen area ratio and the collagen area/total vessel area ratio, respectively, showed an increase in the vehicle-treated SHRSP, and this increase was significantly attenuated by cilostazol treatment. The percentage of small vessels immunopositive for SMemb was also reduced by cilostazol treatment. In the cilostazol-treated SHRSP, microglial activation and the degree of WM lesions were attenuated compared with the vehicle-treated SHRSP. The results indicated that cilostazol attenuates the phenotypic modulation of SMC associated with cerebral small-vessel pathology and WM lesions without causing changes in the blood pressure.

Endothelin Antagonism reverses Upregulated Renin‐Angiotensin System in the hypertrophied Heart of Stroke Prone Spontaneously Hypertensive Rat (SHR‐SP), not in SHR

It is not known whether endothelin (ET)-1 affects the production of angiotensin II (AII) in the heart. We hypothesized that ET-1 may act upstream of renin-angiotensin system (RAS) in hypertrophied heart and tested the hypothesis by investigating the effects of ET blockade on the expression of various components of RAS, including AII in the heart of stroke prone spontaneously hypertensive rats (SHR-SP). SHR-SP were treated for 3 months with SB209670 (ET-A/-B dual receptor antagonist), or saline (vehicle) starting from the prehypertensive stage (6 weeks old). Peptide levels of AII (15-fold higher), and renin, angiotensinogen, angiotensin converting enzyme (ACE) and AII type 1 receptor (AT1R) were significantly upregulated in control SHR-SP, but reversed by long-term ET antagonism: AII type 2 receptor (AT2R) was down-regulated by about 30% in vehicle-treated SHR-SP, and was reversed by ET blockade, including the higher plasma activity of renin and ACE, and plasma levels of AII. The Chymase system was upregulated by 60% in control SHR-SP, and was reversed by ET blockade. Cardiac hypertrophy and myocardial fibrosis at histological level in SHR-SP was ameliorated by ET antagonism, and left ventricular hypertrophy, as revealed by echocardiography in SHR-SP, was also suppressed by ET blockade. These findings indicate that ET antagonism suppressed upregulated RAS in SHR-SP heart, independent of blood pressure. Furthermore, it is suggested that the ET system may act on the upstream of RAS in the heart, and that ET has some regulatory mechanisms on cardiac RAS in SHR-SP, not in SHR. Sponsor: MONBUSHO.

Different Effects of Amlodipine and Enalapril on the Mitogen-Activated Protein Kinase/Extracellular Signal-Regulated Kinase Kinase-Extracellular Signal-Regulated Kinase Pathway for Induction of Vascular Smooth Muscle Cell Differentiation In Vivo

Although recent clinical trials have shown that amlodipine exerts antiatherogenic effects, the mechanism of these effects remains unknown. This study was designed to examine which signal transduction pathway might be important for the antiatherogenic property of amlodipine, as assessed by aortic smooth muscle cell (SMC) phenotypes in hypertension in vivo. Stroke-prone spontaneously hypertensive rats (SHRSP) were randomly treated with a vehicle, amlodipine, or enalapril while Wistar-Kyoto rats (WKY) used as controls were treated with only the vehicle. Both drugs were equally effective at reducing systolic blood pressure, and inhibiting the progression of aortic remodeling and fibrosis in comparison to those of vehicle-treated SHRSP. In the aortas of vehicle-treated SHRSP, the level of contractile-type smooth muscle (SM) myosin heavy chain (MHC) SM2 was significantly lower, whereas the level of synthetic-type MHC NMHC-B/SMemb was significantly higher compared with those in the WKY aortas. Compared to the vehicle-treated SHRSP group, both drugs significantly and equally shifted the aortic SMC phenotype in SHRSP toward the differentiated state by reducing NMHC-B/SMemb and increasing SM2. The levels of MKK6, p38 MAPK, MEK1 and p-42/44 ERK were significantly higher in the vehicle-treated SHRSP than in the WKY. Both drugs significantly reduced these values in the SHRSP aorta. Furthermore, the levels of MEK1 and p-42/44 ERK were significantly lower in the amlodipine- than in the enalapril-treated SHRSP group, whereas enalapril was more effective than amlodipine at increasing p-Akt and endothelial NO synthase in SHRSP aortas, which were significantly lower in the vehicle SHRSP group than in the WKY group. Thus, the MEK-ERK pathway might be one of the crucial determinants of the aortic SMC phenotype activated by amlodipine treatment of hypertension in vivo.

Effect of COX inhibitors and NO on renal hemodynamics following ischemia-reperfusion injury in normotensive and hypertensive rats

The processes involved in the renal damage resulting from ischemia-reperfusion injury are poorly understood. This study examined the contribution of prostaglandins and nitric oxide (NO) in the vascular responses to ischemia-reperfusion injury in the kidneys of normotensive and hypertensive rats. Groups of Wistar and stroke-prone spontaneously hypertensive rats (SHRSP) were dosed with polyethylene glycol vehicle, aspirin (53.5 mg.kg(-1).day(-1)), NO-aspirin (100 mg.kg(-1).day(-1)), or celecoxib (10 mg.kg(-1).day(-1)) for 7 days. On day 7, rats were anesthetized with chloralose/urethane and the left kidney was exposed to a 30-min period of ischemia followed by 90-min reperfusion. Renal cortical and medullary perfusions were monitored throughout using laser-Doppler flowmetry. In the vehicle- and celecoxib-treated Wistar rats, cortical and medullary postischemic perfusion was reduced to 66 and 62% and 53 and 62%, respectively (all P < 0.05), of baseline. The ischemia-induced reductions in cortical and medullary flux were ameliorated in the aspirin and NO-aspirin groups where flux fell to 96 and 78% and 105 and 83%, respectively (P < 0.05). There was a fall in cortical and medullary flux in the postischemic period in the vehicle-treated SHRSP to 82 and 77% (P < 0.05). These findings show that nonselective cyclooxygenase (COX) inhibition, and to an even greater extent NO donation, provided protection to the renal vasculature from ischemic injury in the Wistar rat but not in the SHRSP. This would suggest that prostaglandins are less important in the development of renal ischemia-reperfusion injury during hypertension and both COX isoforms must be inhibited to offset the decrease in renal hemodynamics.

Inhibition of the MEK1 and ERK pathway by amlodipine induces vascular smooth muscle cell differentiation in hypertension

Phenotypic modulation of smooth muscle cells (SMCs) is critical in the progression of atherosclerosis. Recent clinical trials have shown that the long-acting calcium antagonist amlodipine has an antiatherogenic property. The molecular mechanisms of this antiathelogenic property of amlodipine, however, remain unknown. We examined the molecular mechanisms behind the phenotypic modulation of aortic SMCs by amlodipine in stroke-prone spontaneously hypertensive rats (SHRSP). Male Wister-Kyoto rats (WKY) and SHRSPs were randomized and treated with a vehicle, amlodipine (5 mg/kg/day), or enalapril (10 mg/kg/day). Both drugs were significantly and equally effective at reducing systolic blood pressure, aortic morphology and collagen deposition in comparison to vehicle-treated SHRSP aortas. In the vehicle SHRSP aortas, contractile-type SM myosin heavy chain (MHC) SM2 was significantly lower, whereas synthetic-type MHC NMHC-B was significantly higher compared with those in the vehicle WKY aorta. Compared to the vehicle SHRSP group, significantly and to the same extent, both drugs reduced NMHC-B and increased SM2, indicating that both drugs induce the phenotype of SMCs in SHRSP aortas toward the differentiated state. In the vehicle SHRSP group, MKK6, p38MAPK, MEK1 and p-42/44 ERK were significantly increased compared with the vehicle WKY group. Both drugs significantly reduced these values in the SHRSP aorta. Furthermore, amlodipine significantly lowered MEK1 (23%) and p-42/44 ERK (20%) compared with enalapril, reducing MEK1 and p-42/44 ERK to the same levels as in the vehicle WKY group. In contrast, p-Akt and eNOS were significantly lower in the vehicle SHRSP group than in the vehicle WKY group. The two drugs significantly increased p-Akt and eNOS compared with the vehicle SHRSP group. Furthermore, enalapril was more effective than amlodipine at increasing p-Akt and eNOS in SHRSP aortas. Thus, amlodipine inhibited SMC dedifferentiation through the inhibition of the MEK1 and ERK pathway more effectively than did enalapril in SHRSP aortas, suggesting that the MEK1 and ERK pathways might be crucial determinants for the antiatherogenic property of amlodipine in hypertension.

Reduction of Cerebral Infarction in Stroke-Prone Spontaneously Hypertensive Rats by Statins Associated With Amelioration of Oxidative Stress

This study aimed to clarify the effect of statins on spontaneous stroke and to examine the antioxidative effect in artificial transient middle cerebral artery occlusion (tMCAO). Stroke-prone spontaneous hypertensive rats (SHR-SP) were treated with pitavastatin, atorvastatin, simvastatin, or vehicle for 4 weeks. Physiological parameters, serum lipids, and infarct volumes were examined. The markers for oxidative stresses on lipids and DNA were immunohistochemically detected in vehicle-treated or simvastatin-treated SHR-SP with tMCAO. Atorvastatin and simvastatin decreased infarct volumes, with simvastatin most effective. Simvastatin significantly reduced immunoreactivities for oxidative stress markers for lipids and DNA in neurons after tMCAO. The results suggest that the antioxidative properties of statins may be implicated in their beneficial effects against neuronal damage in cerebral ischemia.

Rosuvastatin, but not Simvastatin, Provides End-Organ Protection in Stroke-Prone Rats by Antiinflammatory Effects

Brain abnormalities, preceded by a systemic inflammation, develop in spontaneously hypertensive stroke-prone rats (SHRSP). In this model, we investigated whether the hydrophilic statin, rosuvastatin, influences the development of inflammation associated with brain abnormalities. Because differences in hydrophilicity/hydrophobicity contribute to the differences in statin pharmacology, we also evaluated the effects of simvastatin, a lipophilic molecule SHRSP, fed a high-salt diet, were treated long-term with vehicle or rosuvastatin (1 and 10 mg/kg per day). Brain abnormalities developed after 40+/-5 days and after 60+/-5 days of salt loading, in vehicle-treated and in rosuvastatin-treated (1 mg/kg per day) SHRSP, respectively. After 100 days of treatment, no damage was detectable in 30% of the rats treated with the highest dose of the drug. In comparison with vehicle-treated SHRSP, rosuvastatin treatment attenuated the transcription of monocyte chemoattractant protein-1, transforming growth factor-beta1, IL-1beta, and tumor necrosis factor-alpha in the kidney, and of P-selectin in brain vessels and increased the transcription of endothelial nitric oxide synthase mRNA in the aorta. Urinary excretion of acute-phase proteins increased with time in vehicle-treated animals but remained negligible in drug-treated animals. These effects are independent of changes in physiological parameters. Treatment of SHRSP with simvastatin (2 to 20 mg/kg per day) did not exert any protective effect. Rosuvastatin attenuates inflammatory processes associated with cerebrovascular disease.

Abstracts

Abstracts

Effects of Endothelin Receptor Antagonist on Expression of AT1 and AT2 Receptors in the Heart of SHR-SP

It is already well known that alteration of angiotensin II (Ang II) receptors results in cardiac remodeling in different pathological states, and it is believed that Ang II stimulates the release of endothelin-1 (ET-1). The present study aimed at investigating the interaction between ET-1 and different Ang II receptors in the heart of stroke-prone spontaneously hypertensive rats (SHR-SP). These were treated for 3 months with SB209670, an endothelin-A/endothelin-B dual receptor antagonist, or saline (vehicle) starting from the prehypertensive stage (6 weeks of age). Blood pressure, body weight, heart weight and left ventricular weight were sufficiently decreased after treatment of SHR-SP with SB209670. Ang II type 1 receptor was significantly upregulated in the heart of vehicle-treated SHR-SP compared with the age-matched control, Wistar-Kyoto rat. After endothelin antagonism with SB209670, Ang II type 1 receptor in SHR-SP heart was markedly suppressed. On the other hand, Ang II type 2 receptor was approximately 45% downregulated in the heart of vehicle-treated SHR-SP compared with that of the control, and recovered after endothelin antagonism. The present study demonstrates for the first time the effects of endothelin antagonism on the differential expression and regulation of Ang II receptors in the malignant hypertensive model, SHR-SP, and suggests that the endothelin system may be able to function on the upstream of Ang II signaling.

Anti-inflammatory effects of AT1 receptor blockade provide end-organ protection in stroke-prone rats independently from blood pressure fall.

Spontaneously hypertensive stroke-prone rats (SHRSP) develop hypertension and systemic inflammation, with subsequent brain and renal disorders and early death. We tested the hypothesis that valsartan, an angiotensin II type 1 (AT1) receptor antagonist, exerts protective effects in SHRSP through its anti-inflammatory properties, even in the absence of a blood pressure-lowering effect. SHRSP fed a high-salt diet were treated with vehicle or valsartan (1-10 mg/kg/day). The vehicle-treated rats developed hypertension, proteinuria, progressive kidney disease, and, 40 +/- 5 days from the beginning of the treatment, brain damage as visualized by magnetic resonance imaging. Rats treated with 1 mg/kg/day valsartan developed brain damage after 61 +/- 3 days (p <0.01 versus vehicle-treated rats). No damage showed after 100 days in 80% of the rats treated with 10 mg/kg/day. Valsartan treatment preserved renal structure, by preventing the infiltration of inflammatory cells, and lowered renal expression of monocyte chemoattractant protein-1, transforming growth factor-beta1, and interleukin-1beta, compared with vehicle-treated SHRSP. Urinary excretion of acute-phase proteins increased in the latter but remained negligible in the drug-treated animals. Furthermore, valsartan exerted protective effects also when given after established proteinuria. In SHRSP, blockade of AT1 receptor with valsartan prevents the development of proteinuria, delays the appearance of brain damage, preserves renal structure, and increases survival under stressful conditions. Valsartan exerts its beneficial effects independently of any blood pressure fall and by means of broad anti-inflammatory actions both at local and at systemic levels. These observations indicate that the administration of AT1 receptor antagonists may be useful in pathological situations in which an anti-inflammatory effect is required.

Role of prostaglandin E receptor EP1 subtype in the development of renal injury in genetically hypertensive rats.

One of the major causes of end-stage renal diseases is hypertensive renal disease, in which enhanced renal prostaglandin (PG) E2 production has been shown. PGE2, a major arachidonic acid metabolite produced in the kidney, acts on 4 receptor subtypes, EP1 through EP4, but the pathophysiological importance of the PGE2/EP subtypes in the development of hypertensive renal injury remains to be elucidated. In this study, we investigated whether an orally active EP1-selective antagonist (EP1A) prevents the progression of renal damage in stroke-prone spontaneously hypertensive rats (SHRSP), a model of human malignant hypertension. Ten-week-old SHRSP, with established hypertension but with minimal renal damage, were given EP1A or vehicle for 5 weeks. After the treatment period, vehicle-treated SHRSP showed prominent proliferative lesions in arterioles, characterized by decreased alpha-smooth muscle actin expression in multilayered vascular smooth muscle cells. Upregulation of transforming growth factor-beta expression and tubulointerstitial fibrosis were also observed in vehicle-treated SHRSP. All these changes were dramatically attenuated in EP1A-treated SHRSP. Moreover, EP1A treatment significantly inhibited both increase in urinary protein excretion and decrease in creatinine clearance but had little effect on systemic blood pressure. These findings indicate that the PGE2/EP1 signaling pathway plays a crucial role in the development of renal injury in SHRSP. This study opens a novel therapeutic potential of selective blockade of EP1 for the treatment of hypertensive renal disease.

The angiotensin type 1 receptor antagonist, eprosartan, attenuates the progression of renal disease in spontaneously hypertensive stroke-prone rats with accelerated hypertension.

The effects of the angiotensin type 1 (AT(1)) receptor antagonist, eprosartan, were studied in a model of severe, chronic hypertension. Treatment of male spontaneously hypertensive stroke prone rats (SHR-SP) fed a high-fat, high-salt diet with eprosartan (60 mg/kg/day i.p.) for 12 weeks resulted in a lowering of blood pressure (250 +/- 9 versus 284 +/- 8 mm Hg), renal expression of transforming growth factor-beta mRNA (1.5 +/- 0.2 versus 5.4 +/- 1.4) and the matrix components: plasminogen activator inhibitor-1 (5.2 +/- 1.4 versus 31.4 +/- 10.7), fibronectin (2.2 +/- 0.6 versus 8.2 +/- 2.2), collagen I-alpha 1 (5.6 +/- 2.0 versus 23.8 +/- 7.3), and collagen III (2.7 +/- 0.9 versus 7.6 +/- 2.1). Data were corrected for rpL32 mRNA expression and expressed relative to Wistar Kyoto (WKY) rats [=1.0]. Expression of fibronectin protein was also lowered by eprosartan (0.8 +/- 0.1 versus 1.9 +/- 0.5), relative to WKY rats. Eprosartan provided significant renoprotection to SHR-SP rats as measured by decreased proteinuria (22 +/- 2 versus 127 +/- 13 mg/day) and histological evidence of active renal damage (5 +/- 2 versus 195 +/- 6) and renal fibrosis (5.9 +/- 0.7 versus 16.4 +/- 1.9) in vehicle- versus eprosartan-treated rats, respectively. Our results demonstrated that AT(1) receptor blockade with eprosartan can reduce blood pressure and preserve renal structure and function in this model of severe, chronic hypertension. These effects were accompanied by a decreased renal expression of transforming growth factor-beta1, plasminogen activator inhibitor-1, and several other extracellular matrix proteins compared with vehicle-treated SHR-SP.

Preventative and therapeutic effects of AE0047 on renal injury in stroke-prone spontaneously hypertensive rats.

1. The present study was designed to investigate the preventative and therapeutic effects of AE0047 on renal injury compared with those of nitrendipine in stroke-prone spontaneously hypertensive rats (SHRSP). 2. In the preventative study, drug administration was started before the appearance of renal injury, such as proteinuria. Treatment for 6 weeks with AE0047 (1 and 3 mg/kg, p.o.) led to a dose-related reduction in systolic blood pressure (SBP). Nitrendipine, at doses of 10 and 30 mg/kg, also lowered SBP to a similar degree to that seen with AE0047 at 1 and 3 mg/kg, respectively. 3. In the vehicle-administered SHRSP group, urinary excretion of protein (Uprotein V) increased progressively from 14 weeks of age for another 6 weeks. AE0047 at both doses maintained Uprotein V within normal levels throughout the experimental period. However, the elevation of Uprotein V was only inhibited in the 30 mg/kg nitrendipine-treated group. Urinary N-acetyl-beta-D-glucosaminide (NAG) activity in the vehicle-treated SHRSP group was elevated. Urinary NAG activity remained at a low level only in AE0047-treated groups. 4. Histopathological examination revealed severe lesions (i.e. fibrinoid necrosis, proliferative vasculitis and glomerular lesions) of the kidney in SHRSP. AE0047 treatment at each dose attenuated the development of renal lesions in SHRSP. In contrast, nitrendipine, at 10 mg/kg, was ineffective against the development of renal lesions. Although nitrendipine at 30 mg/kg suppressed the development of renal lesions, this effect was still weaker than that seen with AE0047 at 1 mg/kg. 5. In the therapeutic study, drugs were administered to 17-week-old SHRSP with moderate renal damage for 10 days. Treatment with AE0047 (1 and 3 mg/kg) produced dose-dependent decreases in Uprotein V. In the nitrendipine-treated group, Uprotein V tended to decrease but the changes were not significant. 6. Histopathological studies revealed that 3 mg/kg AE0047 improved renal lesions, such as fibrinoid necrosis, proliferative vasculitis and glomerular lesions, whereas 30 mg/kg nitrendipine did not. 7. Taken together, the results indicate that AE0047 is capable of preventing proteinuria as well as renal lesions, in part via a mechanism independent of its depressor action on SBP. Furthermore, AE0047 improves proteinuria and renal lesions in proteinuria-established SHRSP. Thus, AE0047 may have therapeutic potential in suppressing either the development or the progression of renal disease in hypertensive patients.

The Lipoxygenase Inhibitor Phenidone Protects Against Proteinuria and Stroke in Stroke-Prone Spontaneously Hypertensive Rats

The present study examined whether the dual cyclooxygenase/lipoxygenase inhibitor phenidone would protect stroke-prone spontaneously hypertensive rats (SHRSP) from stroke and hypertensive renal disease. Vehicle-treated SHRSP (N = 6), fed stroke-prone rodent diet and 1% saline, exhibited severe systolic blood pressure elevation (261 +/- 10 mm Hg, mean +/- SEM), marked proteinuria (90 +/- 12 mg/day), and stroke, with an average age at death of 14 +/- 1 weeks. In a second group of six saline-loaded SHRSP, treatment with phenidone (60 mg/kg/day) was started at 8.4 weeks of age. Despite establishment of severe hypertension in this group (274 +/- 10 mm Hg), proteinuria remained at basal levels (28 +/- 13 mg/day), and signs of stroke were absent (P less than .01 v vehicle) through at least 16 weeks of age. Phenidone treatment also prevented the declines in body weight and food intake observed in vehicle-treated SHRSP, and maintained urine volume and saline intake. Serum 12-hydroxy-eicosatetraenoic acid (12-HETE) generation was significantly inhibited greater than 50% in incubates of whole blood from phenidone-treated SHRSP. We have previously shown that agents which interfere with the renin-angiotensin system afford protection from renal and cerebrovascular injury in saline-loaded SHRSP; cyclooxygenase inhibition alone will hasten the onset of these pathologic changes. Whether phenidone, which has been reported to attenuate angiotensin II-mediated effects, affords vascular protection by interference with a lipoxygenase-mediated action of angiotensin II remains to be elucidated.