One-clip Hypertension Research Articles

Genetic inactivation of the B2 receptor in mice worsens two-kidney, one-clip hypertension: role of NO and the AT2 receptor.

Previous studies have suggested that activation of angiotensin II (ANG II) type 2 (AT2) receptors results in nitric oxide (NO) release via activation of endothelial bradykinin B2 (B2R) receptors. The present study was performed to examine the interplay of AT2 and B2R in the development and maintenance of two-kidney, one-clip (2K1C) Goldblatt hypertension. B2R knockout (B2R-/-) mice and their wild-type controls (B2R+/+) underwent clipping of the right renal artery and were infused with either saline (SAL) or PD 123319, an AT2 receptor antagonist (PD), via an osmotic pump implanted intraperitoneally. Systolic blood pressure (SBP) was measured in conscious mice. On day 27, mean arterial pressure (MAP) responses were measured in response to consecutive blockade of AT(2) receptors and NO synthase (NOS). A significant and sustained rise in SBP was observed in both 2K1C B2R+/+ and B2R-/- versus sham-operated groups from day 10 to day 24 after clipping. After this time, SBP rose to significantly higher levels in 2K1C/B2R-/- than in 2K1C/B2R+/+ mice. MAP on day 27 was also higher in 2K1C/B2R-/- than 2K1C/B2R+/+ mice. Chronic PD infusion did not alter the course of hypertension in 2K1C/B2R+/+ or 2K1C/B2R-/- mice as compared with saline-infused mice. Likewise, acute PD infusion did not affect MAP in any of the groups. However, acute NOS inhibition caused significantly greater increases in MAP in 2K1C/B2R+/+ and PD/2K1C/B2R+/+ than 2K1C/B2R-/- and PD/2K1C/B2R-/- mice. These results indicate that B2R inactivation selectively worsens the maintenance phase of 2K1C Goldblatt hypertension and support the notion that B2R-deficient mice exhibit an impaired ability to release NO in response to elevations of ANG II levels. Chronic administration of an AT2 receptor blocker did not modify the course of 2K1C Goldblatt hypertension in either B2R-/- or B2R+/+ mice. Therefore, the role of AT2 receptors in B2R-mediated protection against ANG II-dependent hypertension remains uncertain.

Genetic inactivation of the B2 receptor in mice worsens two-kidney, one-clip hypertension

Objective Previous studies have suggested that activation of angiotensin II (ANG II) type 2 (AT2) receptors results in nitric oxide (NO) release via activation of endothelial bradykinin B2 (B2R) receptors. The present study was performed to examine the interplay of AT2 and B2R in the development and maintenance of two-kidney, one-clip (2K1C) Goldblatt hypertension. Methods B2R knockout (B2R−/−) mice and their wild-type controls (B2R+/+) underwent clipping of the right renal artery and were infused with either saline (SAL) or PD 123319, an AT2 receptor antagonist (PD), via an osmotic pump implanted intraperitoneally. Systolic blood pressure (SBP) was measured in conscious mice. On day 27, mean arterial pressure (MAP) responses were measured in response to consecutive blockade of AT2 receptors and NO synthase (NOS). Results A significant and sustained rise in SBP was observed in both 2K1C B2R+/+ and B2R−/− versus sham-operated groups from day 10 to day 24 after clipping. After this time, SBP rose to significantly higher levels in 2K1C/B2R−/− than in 2K1C/B2R+/+ mice. MAP on day 27 was also higher in 2K1C/B2R−/− than 2K1C/B2R+/+ mice. Chronic PD infusion did not alter the course of hypertension in 2K1C/B2R+/+ or 2K1C/B2R−/− mice as compared with saline-infused mice. Likewise, acute PD infusion did not affect MAP in any of the groups. However, acute NOS inhibition caused significantly greater increases in MAP in 2K1C/B2R+/+ and PD/2K1C/B2R+/+ than 2K1C/B2R−/− and PD/2K1C/B2R−/− mice. Conclusions These results indicate that B2R inactivation selectively worsens the maintenance phase of 2K1C Goldblatt hypertension and support the notion that B2R-deficient mice exhibit an impaired ability to release NO in response to elevations of ANG II levels. Chronic administration of an AT2 receptor blocker did not modify the course of 2K1C Goldblatt hypertension in either B2R−/− or B2R+/+ mice. Therefore, the role of AT2 receptors in B2R-mediated protection against ANG II-dependent hypertension remains uncertain.

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.

Lack of impairment of nitric oxide-mediated responses in a rat model of high-renin hypertension.

1. Angiotensin (Ang) II triggers the expression of a pro- oxidant phenotype in the vascular wall, suggesting that activation of the renin-angiotensin system (RAS) causes endothelial dysfunction in various pathological situations, such as hypertension. However, this hypothesis has been mostly tested in a setting of exogenous administration of AngII. 2. We tested the hypothesis of a role for endogenous activation of the RAS leading to oxidant stress and endothelial dysfunction in a high-renin model of hypertension (i.e. two-kidney, one-clip hypertension) in rats. One month after clipping or sham surgery, aorta were isolated from untreated rats or rats treated by the angiotensin AT1 receptor antagonist irbesartan (10 mg/kg per day). Mesenteric artery segments were also isolated from normotensive or hypertensive rats. 3. Hypertension reduced the relaxations to acetylcholine but did not affect the ratio of contractions to phenylephrine in the presence compared with the absence of a nitric oxide (NO) synthase inhibitor, used as an index of basal release of NO. 4. The free radical scavenger tempol reduced the contractions to phenylephrine in the absence, but not in the presence, of an inhibitor of NO synthesis. This index of free radical-mediated degradation of NO was not affected by hypertension. In parallel, hypertension did not affect the expression of p22phox, a component of the free radical generating enzyme reduced nicotinamide adenine dinucleotide phosphate oxidase. 5. Chronic treatment with the AT1 receptor antagonist decreased blood pressure, moderately improved the response to acetylcholine, but did not affect basal NO release in hypertensive rats, although it did increase basal NO release in normotensive rats. 6. Thus, this model of hypertension is characterized by an impaired stimulated NO release but not of basal NO release in isolated arteries. Furthermore, there was no functional evidence of an increased oxidative stress-mediated impairment of NO release. This is not in favour of a direct link between activation of the RAS and development of endothelial dysfunction in experimental hypertension.

EFFECT OF NITRIC OXIDE INHIBITION ON KIDNEY FUNCTION IN EXPERIMENTAL RENOVASCULAR HYPERTENSION

We examined the effect of acute systemic blockade of nitric oxide (N0) synthesis on blood pressure and renal function in rats with angiotensin II dependent two-kidney, one-clip Goldblatt hypertension. Hypertensive animals had significantly higher blood pressures, plasma NO metabolite concentrations and urinary NO metabolite excretion rates than control rats. Intravenous administration of NG-nitro-L-arginine methylester (L-NAME) (10 mg/kg) increased mean arterial pressure in both hypertensive and control animals with the magnitude of increase being greater in hypertensive than control rats (32±3 vs. 20±2 mmHg,p< 0.05). L-NAME did not affect glomerular filtration rates of normal and clipped kidneys but significantly decreased non-clipped kidney glomerular filtration rate (1.1±0.1 vs. 0.7±0.1 ml/min per g kidney wt, p< 0.05). Blood flow to normal and non-clipped kidneys fell in response to L-NAME. Percent reduction in renal blood flow produced by L-NAME was significantly greater in non-clipped than normal kidneys (38±3 vs. 24±2%,p< 0.05). In contrast, clipped kidney blood flow increased after L-NAME (3.3±0.2 vs. 4.0±0.2 ml/min per g kidney wt,p< 0.05). An identical improvement in clipped kidney blood flow occurred when arterial pressure was raised with aortic constriction indicating that the systemic pressor effect of L-NAME was responsible for this finding. These results indicate that NO plays an important role in systemic and non-clipped kidney hemodynamics in renovascular hypertension. Because NO has little influence on stenotic kidney function, the stimulus for increased NO system activity in this disease appears to be vascular shear stress rather than elevated circulating or intrarenal angiotensin II concentrations.

Monocyte chemoattractant protein-1 and macrophage infiltration in hypertensive kidney injury

We investigated whether monocyte chemoattractant protein-1 (MCP-1) is expressed in hypertensive nephrosclerosis, and tested the effect of angiotensin II type 1 receptor blockade on MCP-1 expression and macrophage (MPhi) infiltration. Rats with two-kidney, one-clip (2K1C) hypertension with and without treatment with the angiotensin II type 1 receptor antagonist valsartan (3 mg/kg/day) were studied. In these animals as well as in spontaneously hypertensive rats (SHR), stroke-prone SHR (SHR-SP), hypertensive mRen-2 transgenic rats (TGR), and respective control strains, MCP-1 expression in the kidney was investigated by Northern and Western blots and by immunohistochemistry. Glomerular and interstitial MPhis were counted. In the nonclipped kidney of 2K1C rats, MCP-1 expression was elevated at 14 and 28 days when significant MPhi infiltration was present. MCP-1 was localized to glomerular endothelial and epithelial cells, interstitial and tubular cells, MPhis, and vascular smooth muscle cells. A similar pattern of MCP-1 staining was present in TGR kidneys, whereas MCP-1 expression was not increased in SHR and SHR-SP. Valsartan reduced but did not normalize blood pressure, blocked the induction of MCP-1 protein in 2K1C kidneys, and decreased interstitial MPhi infiltration significantly. MCP-1 expression is increased in angiotensin II-dependent models of hypertensive nephrosclerosis and is temporally and spatially related to MPhi infiltration. The angiotensin II type 1 receptor mediates the induction of MCP-1.

Renovascular hypertension does not influence repair of glomerular lesions induced by anti-thymocyte glomerulonephritis

Systemic hypertension is a risk factor for progression of renal disease. However, it is not clear whether hypertension has an effect on healing or regression of immune-mediated glomerular damage. To evaluate this effect, we applied a model of glomerulonephritis in rats with two-kidney, one-clip hypertension and studied the effect of hypertension on the healing process of this nephritis. The anti-thymocyte serum (ATS) glomerulonephritis was induced in rats six weeks after initiation of two-kidney, one-clip hypertension, when blood pressure was already increased. Renal structure and function were examined six weeks later. Glomerular expression of alpha smooth muscle actin, the cell cycle inhibitor p27Kip1, and transforming growth factor-beta (TGF-beta) was evaluated by Western blotting. Glomerular proliferation, monocyte infiltration, and fibronectin were examined by immunohistochemistry. Decreased survival, an increase of proteinuria, as well as increased glomerular and tubulointerstitial damage, were found in hypertensive rats compared with normotensive rats. Expression of fibronectin, alpha-smooth muscle actin, TGF-beta, and p27Kip1 was increased in the nonclipped kidney. Complete healing of the glomerular changes associated with the nephritis occurred in normotensive nephritic rats. Surprisingly, complete healing of the nephritis was also found in the clipped as well as nonclipped kidneys of renovascular hypertensive rats. No significant differences could be found for survival, proteinuria, glomerular size, proliferation, monocyte/macrophage infiltration, sclerosis, tubulointerstitial damage, as well as expression of alpha-smooth muscle actin, TGF-beta, fibronectin, and p27Kip1 between hypertensive rats with and without nephritis. These data demonstrate that renovascular hypertension does not influence healing of the glomerular lesions in the anti-thymocyte serum nephritis. This is a rather surprising observation and leaves the question open of which role, in fact, blood pressure may have on the reparative phase of an acute glomerulonephritis, or whether its role depends on the type of glomerulonephritis.

Impaired relaxation to acetylcholine in 2K-1C hypertensive rat aortas involves changes in membrane hyperpolarization instead of an abnormal contribution of endothelial factors

The contribution of endothelial factors and mechanisms underlying decreased acetylcholine-induced relaxation and endothelial inhibitory action on phenylephrine-induced contraction were evaluated in aortas of two-kidney, one-clip hypertensive (2K-1C) and normotensive (2K) rats. Relaxation induced by acetylcholine in 2K-1C precontracted by phenylephrine was lower [Maximum Effect (ME): 71.33±3.36%; p D 2: 7.050±0.03] than in 2K (ME: 95.26±1.59%; p D 2: 7.31±0.07). This response was abolished by N G-nitro- l-arginine (L-NNA) in 2K-1C, but was only reduced in 2K (ME: 29.21±9.28%). Indomethacin had no effect in 2K-1C, and slightly attenuated acetylcholine-induced relaxation in 2K. The combination of L-NNA and indomethacin almost abolished acetylcholine-induced relaxation in 2K-1C, while in 2K, the inhibition (ME: 56.61±8.95%) was lower than the effect of L-NNA alone. During the KCl-induced precontraction, 2K and 2K-1C aortas showed similar acetylcholine-induced relaxation (43.50±5.64% vs. 41.60±4.36%), which was abolished by L-NNA. The levels of cGMP produced in response to acetylcholine were not different between 2K and 2K-1C. The sensitivity to sodium nitroprusside was lower in phenylephrine-precontracted aortas from 2K-1C than 2K, as showed by the p D 2 values (7.72±0.20 vs. 8.59±0.17), and this difference was abolished in aortas precontracted by KCl. The membrane potential was less negative in 2K-1C than in 2K (−41.57±1.19 vs. −51.00±1.13 mV) and hyperpolarization induced by acetylcholine was lower in 2K-1C than in 2K aortas (6.00±0.66 vs. 13.27±1.61 mV). Phenylephrine-induced contraction in aortas with endothelium was similar in both groups, and increased by the endothelium removal. This increase was lower in 2K-1C (from 1.32±0.06 to 1.90±0.21 g) than 2K (from 1.49±0.07 to 2.83±0.18 g). L-NNA and the endothelium removal had similar effect in 2K-1C (1.85±0.18 g) and were lower in 2K (2.18±0.20 g). Indomethacin decreased phenylephrine-induced contraction only in 2K. In conclusion, our major finding was a selective defect in smooth muscle membrane hyperpolarization, which could explain the decreased relaxation to acetylcholine and the attenuated inhibitory effect of endothelium on the contractile function in 2K-1C aortas.

Effect of external stenting and systemic hypertension on intimal hyperplasia in rat vein grafts.

Overdistention of vein grafts in arterial circulation and systemic hypertension are thought to be influential risk factors contributing to vein graft failures. This study tested the effects of external stenting in preventing systemic hypertension and overdistention of the rat vein graft in the long term. Jugular vein grafts were interposed into the carotid artery of normotensive (n = 39) and two-kidney, one-clip hypertensive (n = 30) rats. Jugular vein grafts wrapped with 1.5-mm-diameter polyester stents were used in normotensive (n = 26) and hypertensive (n = 25) rats. The vein grafts were harvested at 1, 2, 4, 8, 12, and 24 weeks after the grafting procedure. The neointimal area and wall thickness were measured by computerized planimetry, and Ki-67 immunohistochemistry was used to detect replicative smooth muscle cells in the graft wall. In each group, intimal hyperplasia was apparent at 1 week and increased gradually to 24 weeks. The number of Ki-67-positive cells was most increased at 2 weeks after the grafting procedure and gradually decreased thereafter. The numbers of Ki-67-positive cells and the extent of intimal hyperplasia were not significantly different between normotensive and hypertensive rats. Both neointima formation and cell proliferation in the graft wall were significantly reduced by external stenting as compared with the results with unstented grafts. Systemic hypertension by itself is not a risk factor for intimal hyperplasia and experimental vein graft failure in the long term. External stenting is effective against intimal hyperplasia, and it is possible to reduce the subsequent atherosclerotic change of the vein graft wall and improve the long-term patency of the vein graft with external stenting.

AT(1) receptor inhibition does not reduce arterial wall hypertrophy or PDGF-A expression in renal hypertension.

To separate the role of ANG II from pressure in hypertrophy of the vascular wall in one-kidney, one-clip (1K1C) hypertension, experimental and sham-operated rats were given the AT(1)-receptor antagonist losartan (20 mg x kg(-1) x day(-1)) or tap water for 14 days. Mean arterial pressure was elevated in both experimental groups compared with controls. Rats were anesthetized with pentobarbital sodium, and the thoracic aorta and carotid, small mesenteric, and external spermatic arteries were harvested and embedded in paraffin. Tissue sections were used for morphological analysis, immunohistochemistry for 5-bromo-2'-deoxyuridine (BrdU) and platelet-derived growth factor (PDGF)-AA, stereological measurements, and in situ hybridization with a (35)S-labeled riboprobe for PDGF-A mRNA. Elevated cross-sectional areas of thoracic, carotid, and small mesenteric artery in 1K1C rats were not reduced by losartan. The internal diameter of the external spermatic artery and microvascular density of the cremaster muscle were reduced in 1K1C rats. The number of BrdU-positive nuclei per cross section did not differ between 1K1C and control arteries. PDGF-A mRNA was elevated in the arterial walls of 1K1C rats compared with controls and was hardly changed by losartan. PDGF-A protein stained strongly in the media of 1K1C arteries and was not inhibited by losartan; it appeared in the adventitia of all aortas and carotid arteries. These observations demonstrate that effects of ANG II mediated through the AT(1) receptor are not necessary for hypertrophy of the vascular wall during 1K1C hypertension or expression of PDGF-A.

Contribution of sarcoplasmic reticulum calcium uptake and L-type calcium channels to altered vascular responsiveness in the aorta of renal hypertensive rats

This study examined whether alterations in intracellular or extracellular Ca 2+ mobilization were related to differences in caffeine and phenylephrine (PHE)-induced contractions between two-kidney, one-clip hypertensive (2K-1C) and normotensive (2K) rat aortas. After depletion and reloading of intracellular Ca 2+ stores, caffeine and PHE-induced contractions in Ca 2+-free solution were increased in 2K-1C. Thapsigargin reduced the contraction to caffeine in 2K-1C and 2K with similar sensitivity. PHE-induced contraction in 1.6-mM Ca 2+ solution was decreased in 2K-1C, and nifedipine was less effective in lowering this response. The responsiveness to extracellular Ca 2+ was decreased in 2K-1C hypertensive rat aortas. Our results indicate an increased intracellular Ca 2+ stores that are not related to alteration in Ca 2+-ATPase function and a lower contribution of L-type channels to the contraction of 2K-1C aortas.

Echocardiographic assessment of cardiac function in conscious and anesthetized mice.

Using a high-frequency linear transducer (15L8), we studied 1) the feasibility of performing echocardiography in nonanesthetized mice compared with mice given pentobarbital sodium (Pento) or a mixture of ketamine and xylazine and 2) the feasibility of echocardiographic evaluation of left ventricular (LV) hypertrophy, dilatation, and function in mice with two-kidney, one-clip hypertension or myocardial infarction (MI). Heart rate (HR) in awake mice was 658 +/- 9 beats/min; Pento and ketamine plus xylazine reduced HR to 377 +/- 11 and 293 +/- 19 beats/min, respectively, associated with a significant decrease in shortening fraction (SF), ejection fraction (EF), and cardiac output (CO) and an increase in LV end-diastolic (LVEDD) and end-systolic dimensions (LVESD). Mice with 4 wk of two-kidney, one-clip hypertension had increased LV mass (15.62 +/- 0. 62 vs. 22.17 +/- 1.79 mg) without altered LV dimensions, SF, EF, or CO. Mice studied 4 wk post-MI exhibited obvious LV dilatation and systolic dysfunction, as evidenced by increased LVEDD and LVESD and decreased SF, EF, and CO. Our findings clearly show the adverse impact of anesthesia on basal cardiac function and the difficulty in interpreting data obtained from anesthetized mice. We believe this is the first study to demonstrate the feasibility of using echocardiography to assess cardiovascular function in the nonanesthetized mouse.

Effect of renovascular hypertension on experimental glomerulonephritis in rats

Systemic hypertension is a major risk factor that determines the rate of progression of kidney disease. The underlying mechanisms, however, are incompletely understood. To gain insight into these mechanisms, the present study was undertaken to characterize the effects of renovascular hypertension on the course of anti-thymocyte antibody-induced glomerulonephritis. Glomerulonephritis was induced in rats 6 weeks after the initiation of two-kidney, one-clip hypertension, when blood pressure was already increased. Structure and function of the clipped and the nonclipped kidney were examined 5 days later. Glomerular filtration rate (GFR) was measured by inulin clearance. The induction of nephritis did not alter the blood pressure in either hypertensive rats or normotensive controls. Albuminuria increased slightly in normotensive rats after the induction of nephritis, whereas no significant differences were found between hypertensive rats with or without nephritis. No significant differences were found for the GFR values of normotensive controls and nephritic animals or for values in the clipped kidney with or without nephritis. However, the GFR of the nonclipped kidney was significantly reduced in nephritic animals as compared with all other groups. Morphologic evaluation revealed that hypertensive rats with nephritis exhibited a combination of characteristics of nephritis and hypertensive glomerular injury. Histologic findings of nephritis, such as glomerular binding of rabbit IgG and glomerular proliferation and mesangial matrix expansion, were similar after the induction of nephritis in controls and in the clipped and nonclipped kidneys of hypertensive animals. However, intraglomerular microaneurysms were significantly more often found in the nonclipped kidneys after the induction of nephritis. Hypertension-induced deterioration of glomerular function was not associated with marked morphologic deterioration but rather with a combination of the characteristics of nephritis and hypertensive glomerular injury.

Effects of niflumic acid on α 1-adrenoceptor-induced vasoconstriction in mesenteric artery in vitro and in vivo in two-kidney one-clip hypertensive rats

The influence of niflumic acid (3 and 10 μM), a Cl − channel antagonist, on cirazoline-induced vasoconstriction in isolated perfused mesenteric artery (5 ml/min) from two-kidney one-clip (2K1C) hypertensive and sham normotensive rats was examined. In addition, the effect of a single i.v. bolus injection of niflumic acid (3 mg/kg) on cirazoline-mediated reduction in vascular conductance in superior mesenteric artery was determined in pentobarbital-anaesthetized hypertensive and normotensive rats. Bolus injections of cirazoline induced a dose-dependent transient increase in the perfusion pressure in vitro. In the presence of niflumic acid, cirazoline-mediated vasoconstriction was significantly inhibited. Cirazoline-induced vasoconstriction in isolated mesenteric beds was also significantly inhibited following perfusion with Cl −-free buffer. Pre-perfusion of mesenteric blood vessels with Cl −-free buffer resulted in a significantly greater inhibition of cirazoline-mediated vasoconstriction in sham normotensive rats than in hypertensive rats. We found that in Cl −-free buffer, cirazoline-mediated vasoconstriction could be further inhibited by niflumic acid. Intravenous infusion of cumulative doses of cirazoline in vivo caused a dose-dependent decrease in superior mesenteric vascular conductance. Pretreatment with niflumic acid significantly impaired cirazoline-mediated decreases in vascular conductance. Our results indicate that chloride ions play an important role in α 1-adrenoceptor-mediated vasoconstriction in mesenteric blood vessels. In addition, the contribution of chloride ions in α 1-adrenoceptor-mediated vasoconstriction in blood vessels from hypertensive rats appears to be reduced.

Role of platelet-activating factor in two-kidney, one-clip hypertension.

Platelet-activating factor (PAF) is a bioactive phospholipid which is a potent hypotensive agent. To investigate the role of PAF in renovascular hypertension, we determined the PAF concentration and its production level assessed by the activity of cholinephosphotransferase (CPT) in renal tissue and examined the effect of a PAF antagonist on the mean arterial pressure (MAP) in control and two-kidney with one clipped (2K1C) hypertensive rats. The concentration of PAF and CPT in the renal medulla and cortex were determined by radioassay. Also, the effect of a PAF antagonist, CV-6209, on MAP was also examined in both 2K1C hypertensive and normal control rats. The PAF concentration and CPT activity were significantly higher in the medulla than in the cortex in both 2K1C hypertensive and normal control rats, and both values in the medulla were also significantly higher in the clipped kidney than in the contralateral unclipped kidney or in control rat kidneys. We also observed a significant negative correlation between the PAF concentration in the medulla, and the medulla weight in the clipped kidney of 2K1C hypertensive rats. Infusion of the PAF antagonist, CV-6209, did not affect MAP in 2K1C hypertensive rats, but was significantly increased (P < 0.05) in control rats. These findings suggest that PAF, whose production is induced by renal ischemia due to renal artery stenosis, plays an important role in the renomedullary vasodepressor system, but the effect of PAF as a vasodilator in the peripheral vessels is limited in 2K1C hypertension.

Leukocyte infiltration and ICAM-1 expression in two-kidney one-clip hypertension

How an increase in blood pressure, in and of itself, induces hypertensive nephrosclerosis is unclear. In an earlier study we found that leukocyte infiltration, proximal tubular cell proliferation, matrix deposition and interstitial fibrosis occur in the unclipped kidney of 2 K 1 C Goldblatt hypertensive rats. In this study we tested the hypothesis that the cell surface adhesion molecule ICAM-1 is expressed on the vascular endothelium and tubular epithelium of unclipped kidneys at 4 weeks. As a positive control, we examined the clipped kidney as well. We found that systolic blood pressure was significantly elevated in renovascular hypertensive rats compared to sham-operated controls after 4 weeks (198 +/- 5 mmHg vs 121 +/- 2 mmHg, P < 0.001). Furthermore, quantitative (densitometry) measurements showed that ICAM-1 expression on vascular endothelium and on tubular cells was significantly increased in unclipped kidneys compared to controls (P < 0.05). The same was true for monocyte and granulocyte infiltration (P < 0.05). These same variables were even more prominent in the clipped kidneys, compared to unclipped and control kidneys (P < 0.05). Our data show that ICAM-1 is expressed in unclipped kidneys exposed to hypertension as well as in clipped kidneys exposed to ischemia. We suggest that mechanical injury induced by increased blood pressure is responsible for an inflammatory adhesion molecule-mediated response and concomitant renal injury.

Chymase is activated in the hamster heart following ventricular fibrosis during the chronic stage of hypertension

Chronic pressure overload induces cardiac tissue remodeling. Chymase is known to regulate matrix metabolism and angiotensin II formation. In the present study, we investigated the pathophysiological functions of chymase in the pressure-overloaded hamster heart induced by a two-kidney, one-clip (2K1C) hypertension procedure. Fibrosis and apoptosis were observed in the pressure-overloaded hearts of 2K1C hamsters 32 weeks after clipping, but these histological changes were not detected at 16 weeks. Heart chymase-like activity of 2K1C hamsters at 32 weeks increased 5.2-fold compared with that at 16 weeks, while angiotensin-converting enzyme was not activated. Chymase might be involved in cardiac tissue remodeling during the chronic stage of hypertension.

The effect of lycium barbarum polysaccharide on two-kidney, one-clip hypertension rats

The effect of lycium barbarum polysaccharide on two-kidney, one-clip hypertension rats

Acute inhibition of nitric oxide synthesis induces anxiolysis in the plus maze test

The involvement of nitric oxide (NO) in anxiety was investigated in rats, using the elevated plus maze test. Acute, but not chronic, systemic treatment with N ω-nitro- l-arginine methyl ester ( l-NAME, 10 and 60 mg·kg −1), an inhibitor of NO synthase, increased the time spent by the rats in the open arms. Both the acute and chronic treatments with l-NAME inhibited NO synthase in endothelial cells and in the central nervous system, as shown by the increase in mean arterial pressure and decreased NO synthase activity in brain tissue. Chronic treatment with l-NAME also decreased the serum nitrate levels. The anxiolysis induced by acute l-NAME treatment is unlikely to be due to hypertension, since two-kidney one-clip hypertension in non- l-NAME-treated rats failed to significantly change exploratory behaviour in the elevated plus maze. These results indicate that acute inhibition of NO synthesis decreases anxiety in rats. © 1997 Elsevier Science B.V. All rights reserved.

The role of thromboxane A2 in the altered microvascular reactivity in two-kidney, one-clip hypertension.

To investigate the nature of the arachidonic acid metabolite involved in the altered reactivity of microvessels of two-kidney, one-clip hypertensive rats and the possible contribution of this product to the elevated blood pressure levels found in two-kidney, one-clip hypertension, mesenteric arterioles either perfused in vitro or studied in vivo were used along with blood pressure determinations. The decreased response to acetylcholine observed was normalized by ridogrel, a thromboxane A2 receptor antagonist, and dazoxiben, a thromboxane A2 synthase inhibitor. The smooth muscle response to nitric oxide, tested with sodium nitroprusside, was unaltered in two-kidney, one-clip hypertensive microvessels. Neither ridogrel nor dazoxiben modified the response to this vasodilator. In contrast, the potentiated response to noradrenaline was corrected by ridogrel and dazoxiben in vitro but not in vivo. Noradrenaline and acetylcholine increased the release of thromboxane A2 from the mesenteric microvessels of two-kidney, one-clip hypertensive rats. Ridogrel and dazoxiben decreased but did not normalize the elevated blood pressure of hypertensive rats. Based on these results, we concluded that: 1) the decreased responsiveness of smooth muscle to acetylcholine resulted from an increase in thromboxane A2 formation rather than a decrease in sensitivity to nitric oxide; 2) thromboxane A2 contributes to the increased noradrenaline response in mesenteric microvessels perfused in vitro while in in vivo other blood borne vasoactive agents may also be involved since the potentiated noradrenaline response was not corrected by inhibiting thromboxane A2 synthesis or receptors; 3) in addition to thromboxane A2, another as yet unidentified factor, may contribute to the elevated blood pressure in two-kidney, one-clip hypertension.