Ligustrazine prevents basilar artery remodeling in two-kidney-two-clip renovascular hypertension rats via suppressing PI3K/Akt signaling

OBJECTIVE

In the present study, we used a two-kidney-two-clip (2k2c) stroke-prone renovascular hypertension rat model (RHRSP) to investigate the protective effects of ligustrazine (TMP) on cerebral arteries and to examine PI3K/Akt pathway behavior under this protection.

METHODS

The cerebral artery remodeling was induced by 2k2c-induced renovascular hypertension. Brain basilar artery tissues were isolated and their histological changes were detected through H&E and EVG staining, α-SMA IHC staining, and transmission electron microscopy at four, eight, and twelve weeks after 2k2c surgery, both with and without TMP treatment. Meanwhile, the ET-1, Ang II, and NO levels in basilar arteries and plasma were determined. Furthermore, the PTEN expression and the activation of PI3K/Akt in basilar artery tissues were detected through IHC and Western Blot. In addition, the primary basilar artery smooth muscle cells (BASMCs) were cultured and TMP protection of BASMCs stimulated with ET-1/Ang II in the presence or absence of insulin-like growth factor 1 (IGF-1) was determined.

RESULTS

TMP attenuated basilar artery remodeling, decreased ET-1 and Ang II levels and increased NO level in basilar arteries and plasma of RHRSP rats. Moreover, TMP reduced BASMCs proliferation upon ET-1/Ang II stimulation. We also found that TMP could effectively suppress the activation of PI3K/Akt in 2k2c-RHRSP rat basilar artery and ET-1/Ang II stimulated BASMCs. Most importantly, IGF-1, as an activator of PI3K/Akt, could damage the protective effect of TMP.

CONCLUSIONS

TMP exerts its protective effects and prevents basilar artery remodeling in RHRSP rats at least partly through the inhibition of PI3K/Akt pathway.

Matrix metalloproteinase (MMP)-2 activation by oxidative stress decreases aortic calponin-1 levels during hypertrophic remodeling in early hypertension

Hypertension is characterized by maladaptive vascular remodeling and enhanced oxidative stress in the vascular wall. Peroxynitrite may directly activate latent matrix metalloproteinase (MMP)-2 in vascular smooth muscle cells (VSMC) by its S-glutathiolation. MMP-2 may then proteolyze calponin-1 in aortas from hypertensive animals, which stimulates VSMC proliferation and medial hypertrophy. Calponin-1 is an intracellular protein which helps to maintain VSMC in their differentiated (contractile) phenotype. The present study therefore investigated whether aortic MMP-2 activity is increased by oxidative stress in early hypertension and then contributes to hypertrophic arterial remodeling by reducing the levels of calponin-1. Male Wistar rats were submitted to the two kidney, one clip (2 K-1C) model of hypertension or sham surgery and were treated daily with tempol (18 mg/kg/day) or its vehicle (water) by gavage from the third to seventh day post-surgery. Systolic blood pressure (SBP) was daily assessed by tail-cuff plethysmography. After one week, aortas were removed to perform morphological analysis with hematoxylin and eosin staining and to analyze reactive oxygen‑nitrogen species levels by dihydroethidium and immunohistochemistry for nitrotyrosine. MMP-2 activity was analyzed by in situ and gelatin zymography and its S-glutathiolation was analyzed by Western blot for MMP-2 of anti-glutathione immunoprecipitates. Calponin-1 levels were identified in aortas by immunofluorescence. SBP increased by approximately 50 mmHg at the first week in 2 K-1C rats which was unaffected by tempol. However, tempol ameliorated the hypertension-induced increase in arterial media-to-lumen ratio and hypertrophic remodeling. Tempol also decreased hypertension-induced aortic oxidative stress and the enhanced MMP-2 activity. S-glutathiolation may be a potential mechanism by which oxidative stress activates MMP-2 in aortas of 2 K-1C rats. Furthermore, calponin-1 was decreased in aortas from 2 K-1C rats and tempol prevented this. In conclusion, oxidative stress may contribute to the increase in aortic MMP-2 activity, possibly by S-glutathiolation, and this may result in calponin-1 loss and maladaptive vascular remodeling in early hypertension.

Matrix Metalloproteinase-2 Activity is Associated with Divergent Regulation of Calponin-1 in Conductance and Resistance Arteries in Hypertension-induced Early Vascular Dysfunction and Remodelling

Matrix metalloproteinase (MMP)-2 participates in hypertension-induced maladaptive vascular remodelling by degrading extra- and intracellular proteins. The consequent extracellular matrix rearrangement and phenotype switch of vascular smooth muscle cells (VSMCs) lead to increased cellular migration and proliferation. As calponin-1 degradation by MMP-2 may lead to VSMC proliferation during hypertension, the hypothesis of this study is that increased MMP-2 activity contributes to early hypertension-induced maladaptive remodelling in conductance and resistance arteries via regulation of calponin-1. The main objective was to analyse whether MMP-2 exerts similar effects on the structure and function of the resistance and conductance arteries during early hypertension. Two-kidney, one-clip (2K-1C) hypertensive male rats and corresponding controls were treated with doxycycline (30 mg/kg/day) or water until reaching one week of hypertension. Systolic blood pressure was increased in 2K-1C rats, and doxycycline did not reduce it. Aortas and mesenteric arteries were analysed. MMP-2 activity and expression were increased in both arteries, and doxycycline reduced it. Significant hypertrophic remodelling and VSMC proliferation were observed in aortas but not in mesenteric arteries of 2K-1C rats. The contractility of mesenteric arteries to phenylephrine was increased in 2K-1C rats, and doxycycline prevented this alteration. The potency of phenylephrine to contract aortas of 2K-1C rats was increased, and doxycycline decreased it. Whereas calponin-1 expression was increased in 2K-1C mesenteric arteries, calponin-1 was reduced in aortas. Doxycycline treatment reverted changes in calponin-1 expression. MMP-2 contributes to hypertrophic remodelling in aortas by decreasing calponin-1 levels, which may result in VSMC proliferation. On the other hand, MMP-2-dependent increased calponin-1 in mesenteric arteries may contribute to vascular hypercontractility in 2K-1C rats. Divergent regulation of calponin-1 by MMP-2 may be an important mechanism that leads to maladaptive vascular effects in hypertension.

Prostaglandins in renovascular and renal hypertension

PG A1, B1, E2, F1,2alpha and PRA have been measured in 8 hypertensive patients with unilateral renal arterial stenosis, 7 hypertensive patients with unilateral renal atrophy and 20 control normotensive subjects. PRA and PGA1 were significantly increased in patients with renovascular hypertension but not in patients with atrophy. PGE2 and PGF1,2alpha were increased in both groups of patients, especially on the stenotic or atrophic side. The increase of PGA1 and PGE2, represents a secondary antihypertensive, diuretic and natriuretic mechanism, the increase of PGF1,2alpha a direct hypertensive mechanism.

Observations on the use and limitations of renal vein renins in hypertensive patients

From our consecutive series of renal vein renin studies in 170 patients with kidney disorders and hypertension, we present those cured by surgical correction of a unilateral renal artery stenosis during the period 1973--75. The renin secretion patterns of these patients range between no demonstrable abnormality, even with a stimulating procedure using dihydralazine 7.5 i.v., and massive renin secretion already during basal conditions. Thus, the renin secretion may not be increased even after stimulation in some patients with durable unilateral renovascular hypertension. This fact may be explained by the rise of the systemic blood pressure, eventually maintained by sodium and water retention and accompanied by adaptive changes in the contralateral kidney. The perfusion pressure is thereby kept normal in the affected kidney, eliminating a stimulus for renin secretion. It is likely that many cases of renovascular hypertension pass through an early stage where no involvement of the renin-angiotensin system may be discovered. Of course, these patients will also benefit from surgery. The conclusion is that renin studies for diagnostic purposes should be performed when patients are on treatment and kept normotensive for some time, and that an additional challenge of the perfusion pressure, i.e., by use of dihydralazine, intravenously should be performed.

Plasma renin activity in renal veins of renovascular patients

PRA was simultaneously measured in both renal veins and in a peripheral vein of patients with essential (6) and renovascular (37) hypertension. In renovascular patients suppression or renin secretion from the contralateral kidney was always observed: otherwise in patients with essential hypertension both kidneys contribute to peripheral PRA. The suppression of renin secretion from the ischemic kidney either by nephrectomy or by revascularization, joins with normalization either of peripheral PRA or of blood pressure. This finding points to the role of the renin-angiotensin system in the genesis of human renovascular hypertension.

Renal secretion of inactive renin

Human plasma contains a non-dialyzable factor which is not enzymatically active in its native form but shows renin-like activity after exposure to low pH (inactive renin). In 3 out of 13 patients with renovascular hypertension the renal to peripheral vein ratio for inactive renin on the affected side was above 1.40, indicating renal release of this form of renin. In 4 cases a high renal to peripheral vein ratio for active renin was associated with a ratio for inactive renin below 0.80, indicating renal activation of circulating inactive renin. The results suggest a renal mechanism for modulating the degree of activation of renin. They have some practical implications for the pre-operative evaluation of patients with renovascular hypertension.

BAEE esterase (kallikrein-like) activity in parotid saliva of normal rats and rats with various forms of experimental hypertension (genuine, renovascular and DOCA salt hypertension)

A technique for continuous and quantitative collection of parotid saliva including salivary flow rate determination for in vitro experiments in rats is described. Kallikrein-like activity in parotid saliva of rats with various forms of arterial hypertension (genuine, renovascular and DOCA salt hypertension) was studied. Kallikrein-like excretion was measured by its estoerolytic activity using benzoyl arginine ethyl ester (BAEE) as a substrate. The levels of kallikrein-like activity in parotid saliva of normotensive control rats ranged between 2.5 and 4.0 mU/min during salivary flow stimulation with pilocarpine. In all forms of experimental hypertension kallikrein-like activity in saliva was increased two-to fourfold. This increase was not related to the activity of the renin-angiotensin system.

Correlation between evolution and treatment of hypertension in unilateral renal disease and values of renin activity in renal venous blood

93 patients with renal hypertension and renal vein PRA determination were studied during 1--5 years follow-up. They were separated in two groups of medical and surgical treatment. Medical treatment is able to normalize blood pressure even in cases with high asymmetric PRA. 9 of 16 patients could be cured or improved in the surgical group and 14 of 22 in the medical group. The best results were obtained if beta-blockers were included in the drug regimen: cured or improved were 7 of 33 patients in medical treatment without beta-blockers, 17 of 28 in surgical treatment, and 31 of 32 in medical treatment including beta-blockers with or without hydralazine and/or diuretics.

Effects of saralasin on blood pressure, renin and renal blood flow in unilateral renovascular hypertension

The effect of saralasin, a competitive inhibitor of angiotensin II, was assessed in hypertensive patients with unilateral renal artery stenosis after furosemide application. A significant fall of systemic arterial blood pressure, an increase of renal venous renin activity, significantly on the stenosed side in patients without arteriosclerosis of the contralateral kidney, and an almost equal decrement of renal blood flow in both kidneys were observed. Conceivably saralasin exerts different sodium-dependent effects on peripheral angiotensin II and specific intrarenal vascular receptors.

Phosphodiesterase 5 attenuates the vasodilatory response in renovascular hypertension

NO/cGMP signaling plays an important role in vascular relaxation and regulation of blood pressure. The key enzyme in the cascade, the NO-stimulated cGMP-forming guanylyl cyclase exists in two enzymatically indistinguishable isoforms (NO-GC1, NO-GC2) with NO-GC1 being the major NO-GC in the vasculature. Here, we studied the NO/cGMP pathway in renal resistance arteries of NO-GC1 KO mice and its role in renovascular hypertension induced by the 2-kidney-1-clip-operation (2K1C). In the NO-GC1 KOs, relaxation of renal vasculature as determined in isolated perfused kidneys was reduced in accordance with the marked reduction of cGMP-forming activity (80%). Noteworthy, increased eNOS-catalyzed NO formation was detected in kidneys of NO-GC1 KOs. Upon the 2K1C operation, NO-GC1 KO mice developed hypertension but the increase in blood pressures was not any higher than in WT. Conversely, operated WT mice showed a reduction of cGMP-dependent relaxation of renal vessels, which was not found in the NO-GC1 KOs. The reduced relaxation in operated WT mice was restored by sildenafil indicating that enhanced PDE5-catalyzed cGMP degradation most likely accounts for the attenuated vascular responsiveness. PDE5 activation depends on allosteric binding of cGMP. Because cGMP levels are lower, the 2K1C-induced vascular changes do not occur in the NO-GC1 KOs. In support of a higher PDE5 activity, sildenafil reduced blood pressure more efficiently in operated WT than NO-GC1 KO mice. All together our data suggest that within renovascular hypertension, cGMP-based PDE5 activation terminates NO/cGMP signaling thereby providing a new molecular basis for further pharmacological interventions.

Soluble epoxide hydrolase inhibition exhibits antihypertensive actions independently of nitric oxide in mice with renovascular hypertension

OBJECTIVE

The present study was performed to examine whether the blood pressure (BP)-lowering effects of soluble epoxide hydrolase (sEH) inhibition in two-kidney, one-clip (2K1C) Goldblatt hypertension are nitric oxide (NO) dependent.

METHODS

Mice lacking the endothelial NO synthase (eNOS) gene (eNOS-/-) and their wild-type controls (eNOS+/+) underwent clipping of one renal artery. BP was monitored by radiotelemetry and the treatment with the sEH inhibitor cis-4-[4-(3-adamantan-1-yl-ureido)cyclohex-yloxy]-benzoic acid (c-AUCB) was initiated on day 25 after clipping and lasted for 14 days. Renal concentrations of epoxyeicosatrienoic acids (EETs) and their inactive metabolite dihydroxyeicosatrienoic acids (DHETs) were measured in the nonclipped kidney. Renal NO synthase (NOS) activity was determined by measuring the rate of formation of L-[(14)C]citruline from L-[(14)C]arginine.

RESULTS

Treatment with the sEH inhibitor elicited similar BP decreases that were associated with increases in daily sodium excretion in 2K1C eNOS+/+ as well as 2K1C eNOS-/- mice. In addition, treatment with the sEH inhibitor increased the ratio of EETs/DHETs in the nonclipped kidney of 2K1C eNOS+/+ as well as 2K1C eNOS-/- mice. Treatment with the sEH inhibitor did not alter renal NOS activity in any of the experimental groups.

CONCLUSIONS

Collectively, our present data suggest that the BP-lowering effects of chronic sEH inhibition in 2K1C mice are mainly associated with normalization of the reduced availability of biologically active EETs in the nonclipped kidney and their direct natriuretic actions.

[Expression and role of soluble epoxide hydrolase in renal tissue of two kidneys one clip hypertension rats model]

OBJECTIVE

To investigate renal expression of soluble epoxide hydrolase (sEH) in 2-kidney-1-clip rats and explore the role of sEH in renal arterial stenosis hypertensive development.

METHODS

Hypertensive models were established in Sprague-Dawly rats by chronic partial occlusion of left renal artery. In the study,16 male Sprague-Dawly rats were randomized into sham operation group and 2-kidney-1-lip (2K1C) group (n=8, each group), and were observed for 40 days. Before operation and every ten days after operation, systolic blood pressure (SBP) was measured and twenty-four-hour urine was collected. At the end of the observation, the blood and kidneys were harvested. The serum Na,24-hour urine protein excretion were measured. Renin activity and angiotensin II concentrition in plasm and renal tissue were evaluated by radioimmunoassay (RIA).The expression of sEH, peroxisome proliferator-activated receptor-γ (PPARγ) in kidneys were assessed by immunohistochemistry and Western blotting. Histology was analysed after kidney sections were stained by Grocott-Gomori methenamine-silver nitrate.

RESULTS

After surgery, the systolic blood pressure in 2K1C group gradually became higher than that in sham group. Urine protein excretion was statistically increased in 2K1C group on the 30 th and 40 th days, while serum sodium was of no significant difference from those of the two groups. Renin-angiotensin system in both clipped and nonclipped kidneys were also invoked by the 2K1C surgery. Both sEH and PPARγ were upregulated in renocortex and renomedulla in 2K1C group. The two groups were compared: in SBP,on the 10 th day, (106.70±7.71) vs.(124.04±6.79) mmHg, P<0.001,and on the 40 th day,(107.80±10.01) vs. (150.40±11.76) mmHg, P<0.001; Urine protein excretion,on the 30 th day,(206.81±37.61)vs.(292.33±20.53)mg/d, P=0.005; Serum sodium, (179.76±29.20) vs. (157.72±51.00)mmol/L, P=0.44; Renin activity[plasm(50.00±13.66) vs.(132.90± 31.22)ng/(L×h),P=0.03; clipped kidney(128.40±36.88)vs.(324.90±56.66)ng/(g×h), P=0.01; nonclipped kidney(103.00±19.87)vs.(345.10±42.68)ng/(g×h), P<0.001]; Ang II [plasm(4 810.00±1 164.00)vs. (10 470.00±1 760.00) ng/L,P=0.02, clipped kidney(735.90±154.40)vs.(2 094.00±372.20)ng/g, P=0.005, nonclipped kidney(648.10±217.90)vs.(1 774.00±206.60)ng/g, P=0.002]; the expression of sEH (sEH/β-actin) in renocortex [clipped kidney (0.33±0.08) vs. (1.73±0.12), P<0.001, nonclipped kidney (0.43±0.09)vs. (0.70± 0.05), P=0.04]; the expression of PPARγ (PPARγ/β-actin) in renocortex [clipped kidney(0.17±0.05) vs. (0.89±0.11), P=0.002, and nonclipped kidney(0.27±0.07) vs. (0.56±0.07), P=0.04]. Clipped kidney showed more severe glomerulosclerosis and tubular atrophy in 2K1C group than in sham group.

CONCLUSION

sEH probably plays an important role in the development of hypertension in the rat models of renovascular hypertension. The activation of PPAR-γ and RAAS by renal arterial stenosis are associated with sEH upregulation, suggesting that they might regulate sEH expression and take part in hypertensive development.

Antioxidant treatment reduces matrix metalloproteinase-2-induced vascular changes in renovascular hypertension

Mounting evidence indicates that structural and functional vascular changes associated with two-kidney, one-clip (2K-1C) hypertension result, at least in part, from altered activity of matrix metalloproteinases (MMPs). Because MMPs are upregulated by increased formation of reactive oxygen species (ROS), we hypothesized that antioxidant approaches could attenuate the increases in MMP-2 expression/activity and the vascular dysfunction and remodeling associated with 2K-1C hypertension. Sham-operated or 2K-1C hypertensive rats were treated with tempol 18 mg/kg/day or apocyanin 25 mg/kg/day (or vehicle). Systolic blood pressure was monitored weekly. After 8 weeks of treatment, aortic rings were isolated to assess endothelium-dependent and -independent relaxation. Quantitative morphometry of structural changes in the aortic wall was studied in hematoxylin/eosin sections. Aortic and systemic ROS levels were measured using dihydroethidine and thiobarbituric acid-reactive substances, respectively. Aortic MMP-2 levels and activity were determined by gelatin and in situ zymography, fluorimetry, and immunohistochemistry. Tempol and apocyanin attenuated 2K-1C hypertension (181+/-20.8 and 192+/-17.6 mm Hg, respectively, versus 213+/-18 mm Hg in hypertensive controls; both p<0.05) and prevented the reduction in endothelium-dependent vasorelaxation found in 2K-1C rats. Tempol, but not apocyanin (p>0.05), prevented the vascular remodeling found in 2K-1C rats (all p<0.01). Tempol was more effective than apocyanin in attenuating hypertension-induced increases in oxidative stress (both p<0.05), MMP-2 levels, and MMP-2 activity in hypertensive rats (all p<0.05). Our results suggest that antioxidant approaches decrease MMP-2 upregulation and attenuate the vascular dysfunction and remodeling during 2K-1C hypertension.

Inhibition of vascular smooth muscle G protein-coupled receptor kinase 2 enhances alpha1D-adrenergic receptor constriction

G protein-coupled receptor kinase 2 (GRK2) is a serine/theorinine kinase that phosphorylates and desensitizes agonist-bound G protein-coupled receptors. GRK2 is increased in expression and activity in lymphocytes and vascular smooth muscle (VSM) in human hypertension and animal models of the disease. Inhibition of GRK2 using the carboxyl-terminal portion of the protein (GRK2ct) has been an effective tool to restore compromised beta-adrenergic receptor (AR) function in heart failure and improve outcome. A well-characterized dysfunction in hypertension is attenuation of betaAR-mediated vasodilation. Therefore, we tested the role of inhibition of GRK2 using GRK2ct or VSM-selective GRK2 gene ablation in a renal artery stenosis model of elevated blood pressure (BP) [the two-kidney, one-clip (2K1C) model]. Use of the 2K1C model resulted in a 30% increase in conscious BP, a threefold increase in plasma norepinephrine levels, and a 50% increase in VSM GRK2 mRNA levels. BP remained increased despite VSM-specific GRK2 inhibition by either GRK2 knockout (GRK2KO) or peptide inhibition (GRK2ct). Although betaAR-mediated dilation in vivo and in situ was enhanced, alpha(1)AR-mediated vasoconstriction was also increased. Further pharmacological experiments using alpha(1)AR antagonists revealed that GRK2 inhibition of expression (GRK2KO) or activity (GRK2ct) enhanced alpha(1D)AR vasoconstriction. This is the first study to suggest that VSM alpha(1D)ARs are a GRK2 substrate in vivo.

Induction of heme oxygenase-1 in renovascular hypertension is associated with inhibition of apoptosis

The goal of this study was to characterize the impact of induction or inhibition of the heme-HO system on renal apoptosis in clipped and non-clipped kidneys from 2K1C hypertensive rats. Male Sprague-Dawley rats had a 0.25 mm silver clip placed around the left renal artery. Four groups of rats were studied: sham operated animals, 2K1C control rats, 2K1C rats received weekly injections of CoPP (5 mg/100 g body wt, administered subcutaneously), and 2K1C rats pretreated with SnMP (5 mg/ 100g body wt, administered intraperitoneally three times a week). The animals were sacrificed three weeks after surgery. We measured systolic blood pressure, plasma renin activity, non-clipped and clipped kidney HO-1 and HO-2 protein expression, HO activity, heme content, nitrotyrosine levels, and activation of selected pro- and anti-apoptotic proteins. Systolic blood pressure and plasma renin activity were significantly higher in 2K1C rats compared to sham rats. Compared to kidneys from sham animals, clipped kidneys from 2K1C rats showed a significant increase in HO-1 expression with increases in HO activity (26%), heme content (47%) and nitrotyrosine levels (49%), accompanied by an increase in caspase-3 and caspase-9 activity. In contrast, non-clipped kidneys from 2K1C rats showed no differences in HO-1 expression, HO activity, heme content, nitrotyrosine levels and caspase activity compared to sham rats. In clipped kidneys from 2K1C rats, inhibition of HO activity by SnMP augmented caspase-3 and caspase-9 activity and decreased expression of the anti-apoptotic Bcl-2 protein, while induction of HO-1 with CoPP strongly inhibited the activity of both caspases and increased the induction of Bcl-2 and Bcl-xl proteins. These findings demonstrate that the clipped kidneys responded to decreased renal perfusion pressure and increased oxidative stress by activation of the heme-HO system, which exerts antiapoptotic action via mechanisms involving decreased caspase-3 and caspase-9 activity, and increased expression of antiapoptotic molecules.

Contribution of different Nox homologues to cardiac remodeling in two-kidney two-clip renovascular hypertensive rats: effect of valsartan

Growing evidences have shown that hypertension, cardiac hypertrophy and fibrosis were associated with an overactivity of NAD(P)H oxidase. It is unknown, however, which isoform of NAD(P)H oxidase yields O(2)*(-) formation in heart and aorta in two-kidney, two-clip (2K2C) hypertensive rats in vivo and thus is responsible for the development of cardiac remodeling. We examined the pathological change of NAD(P)H oxidase homologues and tested the effect of valsartan on the cardiac remodeling in 2K2C renovascular hypertensive rats. Four weeks after male Sprague-Dawley rats accepted 2K2C or sham operation, 2K2C hypertensive (>160 mmHg) rats were divided into vehicle-treated (2K2C) and valsartan (30 mg kg(-1) per day, for 6 weeks)-treated (2K2C+Val) groups, which were compared with sham-operated controls (Sham). At week 10, 2K2C hypertensive rats showed increased serum level of angiotensin II (Ang II), MDA and blood pressure (BP), obvious cardiac hypertrophy and fibrosis, increased O(2)*(-) production and NAD(P)H oxidase activity and expression in aorta and heart. The heart in 2K2C hypertensive rats preferred to use NADH as substrate while the aorta used both NADH and NADPH. Valsartan treatment decreased BP, ameliorated cardiac hypertrophy and fibrosis, decreased O(2)*(-) production and NAD(P)H oxidase activity in aorta and heart. Nox2 and Nox4 protein expression increased in heart, while Nox1 and Nox4 increased in aorta in 2K2C hypertensive rats, which were all normalized after valsartan treatment. In conclusion, these data indicate that different Nox expression might account for substrate preference and the formation of O(2)*(-) by NAD(P)H oxidase resulting from elevated Ang II in the 2K2C model contributes to the development of renovascular hypertension and subsequent cardiac remodeling.

Acupuncture reduces experimental renovascular hypertension through mechanisms involving nitric oxide synthases

OBJECTIVE

To test the hypothesis that acupuncture on stomach 36 point (ST-36) reduces hypertension by activating nitric oxide synthase signaling mechanisms.

METHODS

The authors used the two-kidney, one-clip renal hypertension (2K1C) hamster model with electroacupuncture treatment.

RESULTS

Thirty-minute daily electroacupuncture treatment for 5 days reduced mean arterial pressure from 160.0 +/- 7.6 to 128.0 +/- 4.3 mmHg (mean +/- SEM), compared to 115.0 +/- 7.2 mmHg in sham-operated hamsters. Electroacupuncture increased periarteriolar NO concentration from 309.0 +/- 21.7 nM to 417.9 +/- 20.9 nM in the 2K1C hamster cheek pouch microcirculation when measured with NO-sensitive microelectrodes. Hypertension reduced endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) proteins relative to the sham-operated control, as measured by Western blotting. Electroacupuncture prevented the reduction of eNOS and nNOS associated with hypertension and showed even higher eNOS and nNOS expressions than sham-operated control in stomach and cheek pouch tissues, which are on the stomach meridian. Analysis of liver tissue, a non-stomach-meridian organ, indicated that electroacupuncture did not have a significant benefit in terms of enhanced expressions of eNOS and nNOS in the treated 2K1C hypertensive group.

CONCLUSIONS

Activation of eNOS and nNOS is one of the mechanisms through which ST-36 electroacupuncture reduces blood pressure; this reduction works through the stomach meridian.

Genetic suppression of HO-1 exacerbates renal damage: reversed by an increase in the antiapoptotic signaling pathway

Apoptosis has been shown to contribute to the development of acute and chronic renal failure. The antiapoptotic action of the heme oxygenase (HO) system may represent an important protective mechanism in kidney pathology. We examined whether the lack of HO-1 would influence apoptosis in clipped kidneys of two-kidney, one-clip (2K1C) rats. Five-day-old Sprague-Dawley rats were injected in the left ventricle with approximately 5 x 10(9) colony-forming units/ml of retrovirus containing rat HO-1 antisense (LSN-RHO-1-AS) or control retrovirus (LXSN). After 3 mo, a 0.25-mm U-shaped silver clip was placed around the left renal artery. Animals were killed 3 wk later. Clipping the renal artery in LSN-RHO-1-AS rats did not result in increased HO-1 expression. In contrast to LXSN animals, 2K1C LSN-RHO-1-AS rats showed increased expression of cyclooxygenase 2 (COX-2) and higher 3-nitrotyrosine (3-NT) content as well as increased expression of the proapoptotic protein Apaf-1 and caspase-3 activity. Clipping the renal artery in LXSN rats resulted in increased expression of the antiapoptotic proteins Bcl-2 and Bcl-xl, while clipping the renal artery in LSN-RHO-1-AS rats did not change Bcl-2 levels and decreased the levels of Bcl-xl. Treatment of LSN-RHO-1-AS rats with cobalt protoporphyrin resulted in induction of renal HO-1, which was accompanied by decreases in blood pressure, COX-2, 3-NT, and caspase-3 activity, and increased expression of anti-apoptotic molecules (Bcl-2, Bcl-xl, Akt and p-Akt) in the clipped kidneys. These findings underscore the prominent role of HO-1 in counteracting apoptosis in this 2K1C renovascular hypertension model.

Immuno-proteasome subunit LMP7 is up-regulated in the ischemic kidney in an experimental model of renovascular hypertension

Immuno-proteasome is thought to be responsible for the processing of intracellular antigens and is induced when cells are treated with the inflammatory cytokines promoting cellular immunity. We tested the possibility that immuno-proteasome can be up-regulated in renal cells exposed to a long-lasting ischemia and inflammation in an experimental model of two-kidney, one-clip renovascular hypertension in the rat. Western blotting showed that immuno-proteasome subunit, LMP7, was up-regulated in the clipped ischemic kidney that was atrophic, but not in the contralateral unclipped kidney that underwent compensatory hypertrophy. Immunohistochemical analysis revealed that LMP7 was highly expressed in cortical epithelial and endothelial cells of the ischemic kidney. Surprisingly, the second immuno-subunit, LMP2, was almost undetectable, indicating that renal ischemia may induce exclusively the LMP7 subunit. We also found that renal ischemia neither reduced the SDS-stimulated proteasomal activity nor affected a high level of the PA28 activator. Thus, the results provide evidence that LMP7 immuno-subunit is induced in renal cells exposed to a long-lasting renal ischemia and inflammation, and that there is a direct link between LMP induction and renal atrophy. This opens an opportunity to study a role for LMP-containing proteasomes in the kidneys and other organs undergoing reduction in mass in diseases accompanied by a long-lasting ischemia and inflammatory responses.

Renal-Portal Shunt Ameliorates Renovascular Hypertension in Pigs

BACKGROUND

Renovascular hypertension is the most common curable form of secondary hypertension. Renin angiotensin system activation depends on the balance between renin production by the kidney and renin degradation by the liver. Thus, we aimed to examine whether deviation of renin-rich blood from the affected kidney into the portal circulation (portalization) can ameliorate renovascular hypertension.

METHODS

We selected a porcine model of unilateral renal artery stenosis because the pig's anatomy and physiology are comparable to those of humans and because pigs have already been found capable of developing chronic renovascular hypertension. Angiography and ultrasonography were deliberately used to evaluate renal artery stenosis and the renal-portal shunt. Histology was used to examine the effects of portalization on the kidney and liver after a period of two months.

RESULTS

As expected, following the creation of a left renal artery stenosis both renin activity and mean blood pressure measurements increased from 1.23 +/- 0.06 ng/mL/h and 85.6 +/- 0.5 mm Hg at baseline to 4.59 +/- 0.02 ng/mL/h and 126 +/- 1.76 mm Hg, respectively. After portalization renin activity returned to the normal range (1.59 +/- 0.07 ng/mL/h) followed by a concomitant reduction of mean blood pressure to 91 +/- 2 mm Hg. Moreover, a significant correlation was observed between changes in renin activity and blood pressure measurements during the two stages of the experiment. Both the kidney and liver remained macroscopically and microscopically intact at the end of the experiment.

CONCLUSION

Portalization of the affected kidney can ameliorate renovascular hypertension and therefore, it might be of benefit in those individuals with fibromascular or atheromatous lesions in the renal artery or its branches not amenable to balloon angioplasty or surgical revascularization.

Ebelactone B, an Inhibitor of Extracellular Cathepsin A-Type Enzyme, Suppresses Platelet Aggregation Ex Vivo in Renovascular Hypertensive Rats

The present study was undertaken to investigate whether ebelactone B, an inhibitor of bradykinin and angiotensin I hydrolysis by serine carboxypeptidase Y-like enzymes, could influence platelet aggregation ex vivo in renovascular hypertensive rats (2-kidney, 1-clip Goldblatt model, 2K1C). We found that ebelactone B (5 mg/kg) administrated subcutaneously once a day for 5 days, 5 weeks after the development of hypertension, or a single dose of ebelactone B (0.5 mg/kg) injected intravenously into 2K1C hypertensive rats before the induction of arterial thrombosis, both markedly suppressed collagen-induced platelet aggregation in whole blood. In contrast, inhibition of collagen-induced platelet aggregation was not evident in vitro after pretreatment of the blood with ebelactone B, indicating that ex vivo the antiaggregatory action of this compound can proceed through an indirect mechanism. The injection of ebelactone B did not affect the mean blood pressure of 2K1C hypertensive rats but lowered an elevated extracellular serine carboxypeptidase cathepsin A-like activity. Thus, the data indicate that ebelactone B may be a promising antiaggregatory agent in renovascular hypertension and suggest that 1 of the possible mechanisms through which it exerts this effect may be related to the suppression of cathepsin A-like activity released locally during the development of renovascular hypertension.

Mast cell chymase in the ischemic kidney of severe unilateral renovascular hypertension

Chymase degrades angiotensin I (AI) to form angiotensin II (AII), probably constituting a bypass of the renin-angiotensin cascade. Chymase activity increases in some vascular diseases. In the kidney, an increase in chymase activity was reported in an animal model of ischemic kidney of renovascular hypertension (RVH); however, no such evidence has been provided in humans. We treated a 64-year-old patient with severe unilateral RVH and atherosclerosis, for whom removal of the ischemic kidney was the only option. Using immunohistochemical staining, we investigated chymase activity in the removed kidney and associated artery and vein. An increase in chymase activity, together with mast cells infiltrating the interstitium, was observed where interstitial fibrosis was seen. In the renal artery, where severe atherosclerosis was seen, and also in the vein, mast cell infiltration in the adventitia was accompanied by chymase. The captopril test showed an increase in serum aldosterone level, with a concomitant increase in plasma renin activity and decrease in blood pressure. Because the decrease in blood pressure implies a decrease in circulatory AII levels, it is plausible that in this patient, chymase had a role in AII formation in the adrenal gland to stimulate aldosterone secretion. Thus, by means of captopril, AI levels increased, and chymase may have produced AII in loci tissues, which, in turn, stimulated aldosterone secretion. This is the first report of an increase in chymase activity in the interstitium of an ischemic kidney and renal artery and vein in a patient with RVH and atherosclerosis.

Proteasome inhibitor prevents experimental arterial thrombosis in renovascular hypertensive rats

Recent studies indicate that highly selective proteasome inhibitors can be useful in prevention of some cardiovascular events. Here we demonstrate that proteasome inhibitor, Z-Ile-Glu (Ot-Bu) Ala-Leucinal (PSI), is active in the prevention of platelet-dependent arterial thrombosis induced in renovascular hypertensive rats (two-kidney, one clip Goldblatt model, and 2K1C, n=5). The administration of PSI intravenously at a single dose of 0.3 mg/kg before induction of arterial thrombosis markedly increased carotid final flow rate, as compared to control (vehicle) group (10.36 +/- 1.8 ml/min and 1.2 +/- 1.2 ml/min, respectively), significantly decreased the wet (1.23 +/- 0.23 mg and 4.1 +/- 0.94 mg, respectively), and dry (0.46 +/- 0.145 mg and 1.46 +/- 0.39, respectively) thrombus weight, and completely prevented arterial occlusion. Moreover, platelets from PSI - treated thrombotic 2K1C rats, showed in response to collagen a significant inhibition of aggregation in the whole blood (10.26 +/- 0.6 ohms vs. 15.51 +/- 0.91 ohms in the control group). In contrast, collagen-induced platelet aggregation was not inhibited in vitro, after pre-treatment of the blood with PSI at the concentration of 10 microM that effectively inhibited the 20S proteasome activity in platelets, indicating that ex vivo anti-aggregatory effect of PSI proceeds through an indirect mechanism not associated with suppression of 20S proteasome activity in platelets. In conclusion, our in vivo findings demonstrate that proteasome inhibitor, Z-Ile-Glu(Ot-Bu)Ala-Leucinal, prevents the development of arterial thrombosis in renovascular hypertensive rats and effectively suppresses platelet aggregation by an indirect mechanism. Thus the data provide a new insight into the potential role for the proteasome-dependent pathway in cardiovascular events.

gp91phox-Containing NADPH Oxidase Mediates Endothelial Dysfunction in Renovascular Hypertension

Background— Isoforms of the NADPH oxidase contribute to vascular superoxide anion ( · O 2 − ) formation and limit NO bioavailability. We hypothesized that the endothelial gp91phox-containing NADPH oxidase is predominant in generating the O 2 − to scavenge endothelial NO and thus is responsible for the development of endothelial dysfunction.

Methods and Results— Endothelial dysfunction was studied in aortic rings from wild-type (WT) and gp91phox-knockout (gp91phox −/− ) mice with and without renovascular hypertension induced by renal artery clipping (2K1C). Hypertension induced by 2K1C was more severe in WT than in gp91phox −/− mice (158±2 versus 149±2 mm Hg; P <0.05). Endothelium-dependent relaxation to acetylcholine (ACh) was attenuated in rings from clipped WT but not from clipped gp91phox −/− mice. The reactive oxygen species (ROS) scavenger Tiron, PEG-superoxide dismutase, and the NADPH oxidase inhibitory peptide gp91ds-tat enhanced ACh-induced relaxation in aortae of clipped WT mice. Inhibition of protein kinase C, Rac, and the epidermal growth factor receptor kinase, elements involved in the activation of the NADPH oxidase, restored normal endothelium-dependent relaxation in vessels from clipped WT mice but had no effect on relaxations in those from gp91phox −/− mice. Relaxations to exogenous NO were attenuated in vessels from clipped WT but not clipped gp91phox −/− mice. After removal of the endothelium or treatment with PEG-superoxide dismutase, NO-induced relaxations were identical in vessels from clipped and sham-operated WT and gp91phox mice.

Conclusions— These data indicate that the formation of O 2 − by the endothelial gp91phox-containing NADPH oxidase accounts for the reduced NO bioavailability in the 2K1C model and contributes to the development of renovascular hypertension and endothelial dysfunction.

Study of antihypertensive mechanism of Tribulus terrestris in 2K1C hypertensive rats: Role of tissue ACE activity

Tribulus terrestris is a natural herb used for treating many diseases including hypertension. According to previous reports, aqueous extract of tribulus fruits may have some antihypertensive effect with an unknown mechanism. The present study investigated the antihypertensive mechanism of tribulus in 2K1C hypertensive rats by measurement of circulatory and local ACE activity in aorta, heart, kidney and lung. Four groups of rats were selected; control, sham, operated or hypertensive and tribulus treated hypertensive group. Hypertension was induced using silver clip on renal artery by surgery. Four weeks after surgery, a single daily dose of 10 mg/kg of lyophilized aqueous extract of tribulus fruit were given orally to 2K1C rats for four weeks. ACE activity was determined by high performance liquid chromatography (HPLC). Blood pressure was measured by the tail-cuff method. The systolic blood pressure (SBP) was significantly increased in 2K1C rats compared to control rats. The SBP of tribulus fed hypertensive rats was significantly decreased compared to hypertensive rats. The ACE activity in all tissues of 2K1C rats including: aorta, heart, kidney, lung as well as serum were significantly increased compared to normal rats. The ACE activity in all tissues of tribulus fed hypertensive rats was significantly lower than that of hypertensive rats, which was more pronounced in kidney. These results indicated that there is a negative correlation between consumption of tribulus and ACE activity in serum and different tissues in 2K1C rats.

Fasidotril Eli Lilly

Lilly is developing fasidotril, a diester prodrug of the active metabolite fasidotrilat, for the potential treatment of hypertension and congestive heart failure (CHF). Phase II trials to investigate the potential of fasidotril for the treatment of hypertension and CHF had commenced by the late 1990s, and were ongoing in July 2003 in the US and Europe.

Angiotensinase activities in the kidney of renovascular hypertensive rats

In spite of the well-known contribution of angiotensin II (Ang II) in the pathogenesis of Goldblatt two-kidney one clip (G2K1C) hypertension, the importance of other Ang peptides, such as Ang III, Ang IV or Ang 2-10, is scarcely understood. The functional status of these peptides depends on the action of several aminopeptidases called angiotensinases. The metabolism of Ang III to Ang IV by aminopeptidase M (AlaAP) and of Ang I to Ang 2-10 by aspartyl aminopeptidase (AspAP) was evaluated in the renal cortex and medulla of normotensive (Sham-operated) and hypertensive (G2K1C) rats, treated or not with the AT(1) receptor antagonist valsartan. The results demonstrated a highly significant increase of membrane-bound (MEMB) AlaAP in the cortex of the non-ischemic kidney of G2K1C rats compared with the kidney of normal rats and with the clipped kidney of G2K1C rats. This suggests an increased formation of Ang IV in the non-clipped kidney of G2R1C rats. Valsartan reduced MEMB AlaAP and AspAP activities in the renal cortex of normotensive and in the clipped kidney of hypertensive rats. The reduced metabolism of Ang III may prolong its half-life in valsartan-treated animals. These results suggest a role for AlaAP in renovascular hypertension. In addition, the higher AspAP activity of the renal cortex compared to medulla reflects its relative functional difference between both locations.

Role of macula densa cyclooxygenase-2 in renovascular hypertension

Upregulation of the inducible cyclooxygenase (COX-2) in the macula densa accompanies the activation of the juxtaglomerular apparatus in many high-renin conditions. The functional role of COX-2 in these disease states is poorly understood. We tested whether COX-2 is required to increase renin in renovascular hypertension. Rats with established two-kidney, one-clip (2K1C) hypertension were treated for 2 wk with two different inhibitors of COX-2, NS-398 and rofecoxib, respectively. Hypertension in 2K1C rats was not affected or slightly enhanced by COX-2 inhibition, as measured intra-arterially in conscious animals. The increase in plasma renin activity was also unchanged by both rofecoxib and NS-398. The number of glomeruli with a renin-positive juxtaglomerular apparatus was elevated in clipped kidneys and decreased in contralateral kidneys of 2K1C rats. This pattern was unaltered by COX-2 inhibition. To test the effects of COX-2 blockade on a primarily macula densa-mediated stimulus, we studied salt depletion for comparison. A low-salt diet induced a significant increase in plasma renin activity, which was partially inhibited by treatment with NS-398. We conclude that inhibition of COX-2 in established renovascular hypertension does not affect renin synthesis or release. Thus either COX-2 is not necessary for the macula densa mechanism or the macula densa is not important for maintaining high renin in renovascular hypertension.

Alteration of local ACE activity and vascular responsiveness during development of 2K1C renovascular hypertension

OBJECTIVES

This study sought to examine the correlation between development of hypertension and local, including; aorta, heart, kidney, lung, as well as circulatory (serum) ACE activity in two kidney one clip (2K1C) renovascular hypertension.

METHODS

Ten- to twelve-week-old rats undertaken left renal artery clipping. Experiments were carried out in 2, 4, 8, and 12 weeks after induction of hypertension (2, 4, 8 and 12W). After sacrificing, animals blood and tissues including heart, aorta lung and kidney were dissected out and homogenized in Trizma buffer. ACE activity was determined by hydrolysis of the synthetic substrate, Hip-His-Leu and the amount of hippuric acid liberated from the substrate were analyzed by HPLC. Vascular responsiveness was measured using perfusion pressure method.

RESULTS

The systolic blood pressure (SBP) was gradually increased in 2K1C animals and was markedly higher compared to that of controls. The ACE activity in all tissues from 2K1C was significantly different in all groups of 2, 4, 8, and 12 weeks after surgery. The serum ACE activity of 2K1C was markedly increased in 2 and 4W and reached to plateau in 8 and 12W group. Vascular responsiveness to angiotensin I (AngI) was increased during development of hypertension in all groups of animals.

CONCLUSION

These results indicated that there is a positive correlation between augmentation of blood pressure and local ACE activity in various tissues as well as serum, highlighting the significant contribution of local compared to circulatory ACE activity in development of renovascular hypertension.

Effect of endovascular treatment on nitric oxide and renal function in Takayasu's arteritis with renovascular hypertension

BACKGROUND

Renal involvement in Takayasu's arteritis (TA) effects the disease outcome and endovascular treatment is an effective treatment of choice. We investigated nitric oxide (NO) levels and the effect of endovascular treatment in renovascular hypertensive TA patients.

METHODS

In five hypertensive patients with renal artery stenosis due to TA, serum creatinine, nitrite, nitrate; urinary microalbumin, nitrite, nitrate measurements and blood pressures were recorded at entry and after 24 h and 6 weeks of endovascular treatment.

RESULTS

Serum NO levels were higher in patients than controls (p = 0.008). Serum and urine NO levels increased 24 h after the treatment and decreased after 6 weeks (p = 0.015; p = 0.01, respectively). After the treatment blood pressures decreased. Urinary microalbumin excretions increased after the intervention (p = 0.02) and returned to normal in patients 1 and 4, and decreased in the others. There were no significant differences in estimated glomerular filtration rate (EGFR), serum creatinine, urinary sodium and potassium levels.

CONCLUSION

Increased NO secretion in these patients may contribute to improve the prognosis of renal function through its vasodilator and antiproliferative activities possibly by counterbalancing the excessive vasoconstrictor actions. Endovascular treatment causes a dilatation-induced shear stress that may be responsible for the increased NO release, which in turn leads to the rapid hypotensive response.

Aminopeptidase activity in renovascular hypertension

BACKGROUND

Renovascular hypertension is accompanied by increased renin-angiotensin system activity. Angiotensin II (Ang II) is degraded by aminopeptidases into various metabolites. Increased Ang II production and decreased Ang II degradation may have pathological consequences in maintaining high tissue/plasma Ang II levels.

MATERIAL/METHODS

We report the effects of renovascular hypertension on alanyl- (AlaAP), arginyl- (ArgAP), cystinyl- (CysAP), aspartyl- (AspAP), glutamyl- (GluAP) and pyroglutamyl- (pGluAP) aminopeptidases, using arylamides as substrates. The enzymatic activities were analyzed in plasma, right atrium, lung, left ventricle and aortic ring of rats, normotensive (sham-operated) and hypertensive (Goldblatt two-kidney one-clip, G2K1C), treated or not with the AT1 receptor antagonist valsartan. All determinations were performed six weeks after surgery.

RESULTS

Whereas the atrium exhibited an increase, the lung, ventricle and aorta showed a decrease of aminopeptidases in G2K1C rats. Except in the aorta of normotensive rats, valsartan did not affect aminopeptidases in the groups studied.

CONCLUSIONS

The present study may imply reduced metabolism of angiotensin II in the lung and aorta of G2K1C rats. This down-regulation could prolong the half-life of Ang II and contribute to the maintenance of hypertension. Changes in AP activities did not appear to be part of the action mechanism of AT1 receptor blockade in hypertensive rats

Cyclooxygenase-2 expression and function in renal pathophysiology

Cyclooxygenase (COX) constitutes the rate-limiting enzyme in the biosynthetic cascade of prostaglandin (PG). Evidence has accrued suggesting pathophysiological states with altered COX-2 activity and expression. Recent experimental evidence suggests that COX-2 has a pathogenetic role in some of these derangements. In other situations, the effect of altered COX-2 regulation is unclear or possibly beneficial. These processes suggest new areas for potential use of COX-2-specific inhibitors. Conversely, in some conditions COX-2-specific inhibitors should be avoided. The conventional view is that COX-2 is an inducible enzyme. However, COX-2 is also active in the constitutive production of prostanoids in the kidney. Consequently, the pathophysiological states discussed herein include not only COX-2 induction during inflammation but also derangements in COX-2 expression and function caused by non-inflammatory stimuli.

[The expression of neuronal nitric oxide synthase in caudal medulla of two-kidney one clip Goldblatt hypertension rat]

Experiments were performed in male Sprague-Dawley rats (150-200 g). A silver clip (0.2 mm internal diameter) was placed on the left renal artery of rats. After operation the rats were divided into 4 groups sham group, 2K1C (two-kidney one clip) group, 2K1C+Arg (2K1C and L-Arg 150 mg/kg x d(-1) by drinking) group, and 2K1C+NAME (2K1C and L-NAME 10 mg/kg x d(-1) i.p.) group. The animals were studied at two time points (4 and 7 weeks after operation) corresponding to phases I and II of Goldblatt hypertension. The animals were deeply anesthetized with pentobarbital and perfused by the cardiac route with saline (100 ml) and freshly prepared 4% paraformaldehyde in phosphate buffer (300 ml). The caudal medulla was removed, then placed in 25% sucrose in PB for 12 h in a 4 degrees C fridge. The 40 microm coronal slices of brainstems were cut with cryostat, collected in PBS for nNOS study by immunohistochemistry. The results showed that (1) only a few neuronal nitric oxide synthase (nNOS) positive neurones were found in caudal medulla, including the depressor area of the ventral surface of medulla oblongata (VSMd) and the caudal pressor area (CPA) of the sham operated animals. The number of nNOS positive neurons in caudal medulla was significantly increased in 2K1C Goldblatt hypertension rats at 4 and 7 weeks. (2) The number of nNOS positive neurons in VSMd and CPA were 2K1C+Arg > 2K1C >2K1C +NAME > sham. (3) L-Arg enhanced the expression of nNOS whereas L-NAME inhibited the expression of nNOS in caudal medulla. (4) The character of nNOS expression was similar in Goldblatt hypertension rats at 4 weeks with that of the rats at 7 weeks.

Endothelial nitric oxide synthase protein is reduced in the renal medulla of two-kidney, one-clip hypertensive rats

OBJECTIVE

We studied endothelial nitric oxide synthase (eNOS) expression in the kidneys of two-kidney, one-clip renal hypertensive rats (2K1C) before and after removal of the clip (unclipping, UC). We hypothesised that the haemodynamic changes induced by 2K1C and UC would change eNOS expression in the two kidneys.

METHODS

Six weeks after inducing 2K1C, mean arterial pressure (MAP) was measured in conscious rats and hypertension reversed by UC. Left and right kidney eNOS protein in cortex and outer medulla was semi-quantified using immunoblotting. Groups were; normotensive (n = 10), 2K1C (n = 10), 3 h (n = 10), 48 h (n = 7) and 4 weeks (n = 7) after UC. The effect of 7 days of aldosterone or angiotensin II (Ang II) infusion on medullary eNOS protein was tested as well as the effect of L-NAME (nitric oxide (NO) synthase inhibitor) on medullary blood flow (MBF) in anaesthetized 2K1C.

RESULTS

UC reduced MAP from 178 +/- 5 to 134 +/- 3 mmHg after 3 h and normalized MAP at 48 h and 4 weeks. The medulla from 2K1C kidneys contained about 33% less eNOS protein compared with normotensive kidneys (P < 0.05). This difference was still evident at 3 h (P < 0.05), but completely reversed at 48 h and 4 weeks after UC. Similar levels of eNOS expression were seen in the left and right kidney at all time points. Cortical eNOS was increased in kidneys from 2K1C. Neither Ang II nor aldosterone affected eNOS expression in the medulla. MBF was under similar influence of NO in 2K1C compared with normotensive kidneys.

CONCLUSIONS

2K1C is associated with reduced levels of eNOS protein in the renal medulla of both clipped and contralateral kidney. eNOS expression in right and left kidney was not changed despite expected large changes in haemodynamics of the two kidneys. The reduced level of eNOS may be associated with a reduction in MBF and thus be of patho-physiological importance in renovascular hypertension.

Effect of valsartan on angiotensin II- and vasopressin-degrading activities in the kidney of normotensive and hypertensive rats

Valsartan, a selective antagonist of angiotensin II at the AT(1) receptor subtype, is an efficacious, orally active, blood pressure-lowering agent used in hypertensive patients. Given that aminopeptidases (APs) play a major role in the metabolism of local peptides involved in blood pressure control, studying them helped us to understand cardiovascular control. We studied the effect of valsartan on angiotensin II- (GluAP) and vasopressin- (CysAP) degrading activities in the kidney in the rat model of renovascular hypertension, Goldblatt two-kidney one-clip. GluAP and CysAP in renal cortex and medulla exhibited different responses to hypertension and valsartan treatment. In the renal cortex, GluAP decreased in clipped and non-clipped kidneys of hypertensive animals. However, while hypertension did not affect GluAP in the clipped kidney medulla, the non-clipped kidney exhibited an increase in soluble and a decrease in membrane-bound activity. Valsartan decreased soluble GluAP in the medulla of normotensive and hypertensive animals. In the renal cortex, CysAP activity was mainly downregulated following hypertension. Valsartan decreased soluble CysAP activity in sham-operated, but not in hypertensive animals. The renal medulla showed a significant valsartan-related decreased activity in clipped and non-clipped kidneys of both sham-operated and hypertensive animals. These results suggest a functional relationship between the AT(1) receptor and vasopressin-degrading activity.

Renal cortical remodelling by NO-synthesis blockers in rats is prevented by angiotensin-converting enzyme inhibitor and calcium channel blocker

The cortical remodelling was studied when chronically nitric oxide synthesis (NOs) blockade (L-NAME-induced) hypertensive rats are simultaneously treated, or not, with angiotensin-converting enzyme inhibitor or calcium channel blocker. Four groups of eight rats each were studied as follows: Control (C), L-NAME (L), L-NAME+Enalapril (L+E) and L-NAME+Verapamil (L+V). The systolic blood pressure (SBP) was weekly recorded. The cortex of the left kidneys was analysed according to the vertical section design. The volume-weighted mean glomerular volume (VWGV) was made through the "point-sampled intercepts" method. Enalapril and verapamil were efficient in reducing the SBP in rats submitted to NOs blockade. Glomeruli had considerable alterations in L group rats (glomerular hypertrophy or sclerosis) and tubular atrophy. The VWGV was 100% greater in L group rats than in the C group rats, while it was 30% smaller in L+E and L+V groups than in L group. The tubular volume was 30-50% greater, while the tubular length was 20-30% smaller in the L group than in the other groups. The renal cortical region showed glomerular sclerosis/hypertrophy and tubular remodelling in rats with NOs blockade that was efficiently prevented with the simultaneous treatment with enalapril or verapamil.

Renal expression of aminopeptidase A in rats with two-kidney, one-clip hypertension

BACKGROUND

Angiotensin II (ANG II) is a major factor involved in the progression of chronic renal disease. Although the generation of this vasoactive peptide has been investigated in great detail, only a few studies have hitherto addressed the metabolism of ANG II into fragments such as angiotensin III and IV (ANG III, IV) which may exert physiological effects independent of ANG II. Aminopeptidase A (APA) is the major enzyme degrading ANG II. The aim of the current study was to evaluate glomerular APA expression in rats with two-kidney, one-clip hypertension.

METHODS

The left renal artery was restricted with a 0.2-mm silver clip. Kidneys were harvested 1 and 4 weeks after surgery. APA enzyme and protein expression was evaluated in kidney sections. Total APA enzyme activity and mRNA expression was assessed in isolated glomeruli. Degradation of exogenous ANG II by isolated glomeruli was measured with reverse-phase high-performance liquid chromatography.

RESULTS

APA enzyme activity, protein, and mRNA expression were stimulated in the clipped kidney 1 week after surgery compared with the contralateral kidney or normal controls. In contrast, 4 weeks after clipping APA activity and expression was higher in the contralateral kidney. In parallel to these findings, degradation of ANG II was greatest in isolated glomeruli obtained from the clipped kidney after 1 week. However, preparations from the contralateral kidney 4 weeks after surgery were more active in the metabolism of exogenous ANG II.

CONCLUSION

The present study provides evidence that APA is complexly regulated in in vivo situations with an activated local renin-ANG II system. ANG II appears to play a direct role in this regulation. However, since conversion of ANG II to ANG III by APA is the initial step leading to the formation of ANG IV which may exert detrimental effects not mediated through classical ANG II receptors, a local increase in APA activity may contribute to the progression of chronic renal disease even during complete AT(1)-receptor blockade.

Glomerular expression of endothelial nitric oxide synthase in deoxycorticosterone acetate-salt-treated rats

1. In the present study, we investigated the relationship between chronic volume loading and glomerular endothelial nitric oxide synthase (eNOS) expression. Immunohistochemical expression of eNOS in glomeruli was semiquantified by graded scores of staining intensity. Each glomerulus was isolated by microdissection and mRNA expression was detected by reverse transcription-polymerase chain reaction (RT-PCR) in desoxycorticosterone acetate (DOCA)-salt-treated rats. 2. Glomerular expansion and dilatation of tubules were the main histological findings and glomerular and vascular injury scores were significantly higher in the DOCA-salt-treated group than in the control group. Endothelial NOS staining in glomeruli in DOCA-salt-treated animals was 81.4% lower than in control animals. Endothelial NOS mRNA was also detected at a very low rate in the kidney of treated rats compared with control rats (22/80 vs 74/80 glomeruli, respectively). 3. These results suggest that eNOS protein and mRNA expression in glomeruli was reduced by DOCA-salt loading. Chronic volume loading may damage the glomerulus and this may be mediated, at least in part, by disruption of eNOS.

Angiotensin converting-like enzymes from urine of untreated renovascular hypertensive and normal patients: purification and characterization

Angiotensin converting-like enzymes (ACE) were isolated from urine of normal (P0N, P1N and P2N) and untreated renovascular hypertensive (P0, P1 and P2) patients. The urine were submitted to ion exchange chromatography. Enzymes P0 and P0N were eluted with the equilibrium buffer (0.02 M Tris-HCl, pH 7.0), while P1, P1N, P2 and P2N with ionic strength linear gradient of 0.02-0.5 M Tris-HCl, pH 7.0 in 0.7 mS and P2 and P2N in 1.2 mS conductance. The active fractions were submitted to gel filtration in Sephadex G-150, equilibrated and performed with 0.05 M Tris-HCl/0.15 M NaCl buffer, pH 8.0. All enzymes were homogeneous when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) (molecular mass: P0, P2 and P2N about 60 kDa; P1, 95 kDa and P21N 170 kDa). The enzymes were recognized by Y1 polyclonal antibody raised against human renal ACE. The K(M) values were in millimolar order for hippuryl-L-His-Leu (HHL) while for benzyloxycarbonyl-Phe-L-His-Leu (ZFHL) they were in 10(-4) M order. The enzymes were able to hydrolyze angiotensin I (AI) (P0 and P0N about 25%, P1 and P1N about 70%, P2 100% and P2N 66%) and bradykinin (BK) (P0N 22%, P1N 81%, P2N 62%, P0 and P1 50% and P2 35%), and their activities were inhibited by captopril.

Angiotensin-converting enzyme gene I/D polymorphism and carotid artery disease in renovascular hypertension

There is evidence linking the activation of the renin-angiotensin system (RAS) with target organ damage in renovascular hypertension (RVH). A genetic association of the DD genotype of the angiotensin-converting enzyme (ACE) gene with cardiovascular complications has been found in various clinical conditions. The aim of our study was to determine whether the insertion/deletion (I/D) polymorphism of the ACE gene is associated with the high prevalence of target organ damage reported in RVH. A total of 65 atherosclerotic patients (age 68.2 +/- 5.2 years) with RVH and 49 atherosclerotic patients (age 68.0 +/- 6.3 years) with essential hypertension (EH) were sequentially enrolled when attending the outpatient clinic for specialist assessment of their vascular disorder. Cardiac, renal, and vascular involvement were assessed in both groups and blood was taken for genetic analysis. Patients with RVH had a higher prevalence of left ventricular hypertrophy (LVH), carotid artery disease, and albuminuria than those with EH. In RVH, but not in EH, the DD genotype was significantly associated with severe arterial disease. In RVH, carotid disease (lumen narrowing >60%) was present in 62% of DD patients versus 25% of the other genotypes (OR = 4.90, 95% CI: 1.70-14.13). Such an association was also present in peripheral vascular disease: 72.4% in DD patients versus 41.6% in the other genotypes (OR = 3.67, 95% CI = 1.29-10.36). Logistic regression analysis showed that the DD genotype was the strongest predictor of risk of severe carotid disease. We conclude that, in atherosclerotic RVH, there is an association of the severity of vascular disease with the DD genotype of the ACE gene.

Regulation of Na,K-ATPase activity in renal basolateral membrane of 1-clip-1-kidney hypertensive rat

The changes of Na,K-ATPase activity and its regulation have been investigated in the renal cortex of 1-clip-1-kidney hypertensive rat. Ouabain-sensitive Na,K-ATPase activity (Emax) and [3H]ouabain-binding site (Bmax) in the hypertensive rat were slightly increased than those in the control. The levels of Na,K-ATPase alpha 1- and beta 1-subunit mRNA of the renal cortex in hypertensive rat were more increased than those in the control. Their increases were repressed by actinomycin-D, but not altered or more increased by cycloheximide. These results suggest that the increase of Na,K-ATPase activities and ouabain binding sites in 1-clip-1-kidney hypertensive rat may be correlated with the increases of gene expression in transcription level and/or of mRNA stability of Na,K-ATPase.

Roles of vascular angiotensin converting enzyme and chymase in two-kidney, one clip hypertensive hamsters

BACKGROUND

A chymase-dependent angiotensin II-forming pathway is present in human vascular tissues; however, the role, if it plays any, of chymase in the pathogenesis of hypertension is not known. When investigating the role of chymase, it is important to recognize marked differences in vascular angiotensin II-forming systems among species. We found recently that hamsters, like humans, possess the dual angiotensin II-forming system.

OBJECTIVE

To analyze the potential involvement of angiotensin converting enzyme and chymase in the pathogenesis of hypertension, and to further characterize the efficiency of angiotensin converting enzyme inhibitors and angiotensin II receptor antagonists for the treatment of hypertension.

METHODS AND RESULTS

The mean arterial pressure in the two-kidney, one clip hamster model had increased significantly 2 weeks after clipping (acute stage), reached a peak after 4 weeks, and was sustained at the high level until 32 weeks after clipping (chronic stage). Plasma renin activity increased markedly during the acute stage, but returned to the normal level during the chronic stage. Vascular angiotensin converting enzyme activity during 4-32 weeks after clipping was significantly higher than that in the control hamsters. By contrast, vascular chymase was not activated throughout the experimental period. Administrations of an angiotensin converting enzyme inhibitor, trandolapril, and an angiotensin II receptor antagonist, CV-11974, equally lowered the mean arterial pressure during the acute and chronic stages.

CONCLUSIONS

Vascular angiotensin converting enzyme plays a predominant role in the maintenance of two-kidney, one clip hypertension in hamsters, which, like humans, possess a dual system of formation of angiotensin II. Vascular chymase was not involved in the pathogenesis of two-kidney, one clip hypertension in the hamster.

[Changes of activities of MLCK and dephosphatase in different arterial vessels from hypertensive rats]

The changes of activities of myosin light chain kinase (MLCK) and Ca2+/CaM-PP in different arterial vessels from hypertensive and normotensive rats were studied. The results were as follows. The MLCK activity of different arteries of spontaneous hypertensive rats (SHR) was different with the order of aorta (A) >> caudal artery (CA) >> mesenteric artery (MA), while in WKY rats the order of activity among different arteries is A << CA and MA and MA Ca2+/CaM-PP is obviously higher than in SHR. In renal hypertensive rats the activities of Ca2+/CaM-PP in different arteries are not quite different from those of the Wistar rats. The above results suggest that higher activities of MLCK or/and lower activity might be related to vasocontraction and hypertension.

Coordinate expression of cyclooxygenase-2 and renin in the rat kidney in renovascular hypertension

Prostaglandins contribute to the regulation of renin synthesis and secretion. We tested the hypothesis that the inducible isoform of prostaglandin G/H synthase, cyclooxygenase-2, contributes to the stimulation of renin synthesis in renovascular hypertension. The expression of cyclooxygenase-2 and renin was investigated in the kidneys of rats with two-kidney, one-clip renovascular hypertension or sham operation. Systolic blood pressure was increased 2 weeks after clipping (153+/-7 versus 112+/-4 mmHg in controls, n=6 each, P<.05) and continued to rise until 4 weeks. Cyclooxygenase-2 mRNA levels were increased in clipped kidneys but remained unchanged or slightly decreased in nonclipped kidneys. Cyclooxygenase-2 protein was expressed mainly in the macula densa and occasionally in distal tubular cells not associated with the macula densa. Two weeks after clipping, the percentage of juxtaglomerular apparatus staining positive for cyclooxygenase-2 was 27.8+/-3.6 in clipped kidneys, 3.1+/-0.4 in contralateral kidneys, and 8.0+/-1.3 in controls; the percentages for immunoreactive renin staining in the afferent arteriole were 33.6+/-2 in clipped kidneys, 1.9+/-0.5 in contralateral kidneys, and 12.4+/-4.0 in controls, respectively. Similar parallel changes in renin and cyclooxygenase-2 staining were observed 4 weeks after clipping. The percentage of cyclooxygenase-2-positive juxtaglomerular apparatus correlated positively with the percentage that was renin positive (r=0.78, P<.05). Double immunostaining showed coexpression of cyclooxygenase-2 and renin protein in the same juxtaglomerular apparatus. Our data are consistent with a role for macula densa cyclooxygenase-2 in the regulation of renin in renovascular hypertension.

Renal aminopeptidase activities in animal models of hypertension

Aminopeptidase activity (AP) has been implicated in the metabolism of renal and circulating vasoactive peptides. This activity is involved in the pathogenia of hypertension, essentially in spontaneously hypertensive rats. However, no other animal models, which develop hypertension by other different ways, have been used to study the possible role of aminopeptidase activity. To investigate the role of this activity in the pathogenesis of hypertension, angiotensinase A activity (glutamyl-AP and aspartyl-AP), aminopeptidase M activity (alanyl-AP), aminopeptidase B activity (arginyl-AP), pyroglutamyl-AP, and cystinyl-AP were measured in the serum and kidney of two experimental animal models of renovascular hypertension: Goldblatt two-kidney one clip (G2K-1C) and low renal mass rats (LRM). No differences were found in serum levels of AP in LRM or G2K-1C in comparison with their respective controls. In LRM rats there was a significant decrease in membrane-bound angiotensinase A (glutamyl-AP), arginyl-AP and alanyl-AP activities. In G2K-1C rats there was a significant decrease in soluble and membrane-bound angiotensinase A activity (aspartyl-AP). Our results suggest that AP activities play a role in the regulation of renal vasoactive peptides, and respond differently depending on the cause of hypertension.