Clip Rats Research Articles

Renal damage in the non‐clipped kidney in two kidney one clip rat is most pronounced in the juxtamedullary cortex.

Renal damage in old spontaneous hypertensive rats (SHR) was found to start in the juxtamedullary cortex (JMC) and extend towards the outer cortex (OC), with a clear difference in gene expression for the enzymes involved in collagen metabolism in the two compartments. In the present study we studied the progression of hypertensive renal damage in the non‐clipped kidney of two kidney, one clip (2k1c) rats, 6, 16 and 24 weeks after clipping. The mean arterial pressure was increased after 2‐4 weeks, and was 166±9 mmHg in the 2k1c group and 116±7 mmHg in the control group after 24 weeks. The 6 and 16 week group showed no histological damage, or up regulation of the mRNA expression of collagen type‐1‐A1 (col1a1), procollagen‐n‐ and c‐peptidase (n‐pep, c‐pep). At sacrifice the 24 week 2k1c group had a protenuria of 760±251 mg/mmol creatinine, higher than in the control group (92± 12 mg/mmol creatinine, p<0.05). The mRNA expression of col1a1 and n‐pep in the JMC in 2k1c was higher than in the OC, and higher than in the control group. We found no difference in the expression of c‐pep.In conclusion, it looks like our previous findings of a progression of renal damage from JMC towards OC in SHR, is a systematic feature of hypertensive renal damage. The increased expression of n‐pep may be an important mechanism in the increased collagen deposition.The study was funded by the University of Bergen and Helsevest, Norway

T05-P-14 Mechanisms of sex differences in cardiovascular resistance to stress and development of hypertension

Objective The goal of this study was to estimate sex particularities in activity of cholinergic, adrenergic and nitrergic influence to cardiovascular system in normotensive and hypertensive (2 kidney, 1 clip) rats under rest and stress conditions. Methods Rats of both sexes were instrumented with catheters in artery for measuring of mean arterial pressure (MAP) and heart rate (HR) responses to acetylcholine (0.3 μg/100g), adrenaline (10 μg/100g) and Nω-nitroarginine (L-NNA, 0.25 mg/100g) injection. Results We found that hypertension was attenuated in females vs. males. During stress both normotensive and hypertensive females demonstrated more favorable pattern of MAP and HR than males. The cardiovascular sensitivity to stimulate of cholinergic and adrenergic influence was higher in normotensive group vs. hypertensive state under rest and stress. Interestingly, that normotensive and hypertensive females compared with males of both groups have greater vascular reactivity to acetylcholine/adrenaline and compensatory myocardial responses in normal and, especially, stress conditions. The vascular sensitivity to nitric oxide blockade was decreased in hypertensive rats vs. normotensive animals. Impotence, that we found more pronounced MAP response to L-NNA in both healthy and hypertensive females compared with healthy and hypertensive males under rest and stress. Conclusions Thus, an enhanced cardiovascular sensitivity to autonomic and nitrergic influence in normotensive and hypertensive females compared with males of both groups may contribute to 1) higher cardiovascular adaptation to stress, 2) a lower incidence of hypertension, 3) development less severe of hypertension in female gender.

(Pro)Renin Receptor Peptide Inhibitor “Handle-Region” Peptide Does Not Affect Hypertensive Nephrosclerosis in Goldblatt Rats

The (pro)renin receptor [(P)RR], a new component the renin-angiotensin system, was cloned recently. The (P)RR promotes direct mitogen-activated protein kinase signaling and nonproteolytic prorenin activation. We investigated the role of a (P)RR blocker, a peptide consisting of 10 amino acids from the prorenin prosegment called the "handle-region" peptide (HRP), on target organ damage in renovascular hypertensive 2-kidney, 1-clip (2K1C) rats. Vehicle-treated 2K1C rats were compared with HRP-treated 2K1C rats (3.5 mug/kg per day) and sham-operated controls. Vehicle-treated 2K1C rats developed hypertension (186+/-17 mm Hg), cardiac hypertrophy (3.16+/-0.16 mg/g), renal inflammation, fibrosis, vascular, and tubular damage. Chronic HRP treatment did not affect blood pressure (194+/-15 mm Hg), cardiac hypertrophy (2.97+/-0.11 mg/g), or renal damage. Furthermore, we investigated the renal renin and (P)RR expression. The clipped kidney of 2K1C and HRP-treated 2K1C rats showed a higher renin expression and juxtaglomerular index compared with sham-operated kidneys. The unclipped kidney showed suppressed renin expression. In contrast, (P)RR mRNA expression was not altered in any group. Plasma renin activity and aldosterone were increased in 2K1C rats compared with sham controls. HRP-treated 2K1C rats tended to lower plasma renin activity but showed similar aldosterone levels as vehicle-treated 2K1C rats. Our results indicate that blockade of the (P)RR with HRP does not improve target organ damage in renovascular hypertensive rats.

Rat retinal morphological changes after optic nerve crush

目的 探讨大鼠视神经夹伤后视网膜病变的时序性变化.方法 建立大鼠视神经夹伤模型.分别于伤后1、3、7、15、30 d光镜下计数视网膜神经节细胞(RGCs)数目的变化.结果 大鼠视神经夹伤诱导RGCs较正常眼明显减少.结论 应用40 g力视神经夹建立的定量视神经损伤动物模型是可行的,并可应用于视神经损伤修复的研究中。

Caveolae Dysfunction Contributes to Impaired Relaxation Induced by Nitric Oxide Donor in Aorta from Renal Hypertensive Rats

Relaxation induced by nitric oxide (NO) donors is impaired in renal hypertensive two kidney-one clip (2K-1C) rat aortas. It has been proposed that caveolae are important in signal transduction and Ca2+ homeostasis. Therefore, in the present study we investigate the integrity of caveolae in vascular smooth muscle cells (VSMCs), as well as their influence on the effects produced by NO released from both the new NO donor [Ru(NH.NHq) (terpy)NO+]3+ (TERPY) and sodium nitroprusside (SNP) on 2K-1C rat aorta. The potency of both TERPY and SNP was lower in the 2K-1C aorta that in the normotensive aorta [two kidney (2K)], whereas the maximal relaxant effect (ME) was similar in both 2K-1C and 2K aortas. In the 2K aorta, methyl-beta-cyclodextrin (CD) reduced both the potency of TERPY and SNP, and their ME compared with the control, but it had no effect on the potency and ME of these NO donors in 2K-1C aortas. The decrease in cytosolic Ca2+ concentration ([Ca2+]c) induced by TERPY was larger in 2K than in 2K-1C cells, and this effect was inhibited by CD in 2K cells only. Aortic VSMCs from 2K rats presented a larger number of caveolae than those from 2K-1C rats. Treatment with CD reduced the number of caveolae in both 2K and 2K-1C aortic VSMCs. Our results support the idea that caveolae play a critical role in the relaxant effect and in the decrease in [Ca2+]c induced by NO, and they could be responsible for impaired aorta relaxation by NO in renal hypertensive rats.

Prevention of Hypertension and Organ Damage in 2-Kidney, 1-Clip Rats by Tetradecylthioacetic Acid

Dietary lipids are reported to affect the blood pressure in both humans and experimental animal models with hypertension. In the present study, 2-kidney, 1-clip (2K1C) hypertensive rats were treated with the modified fatty acid tetradecylthioacetic acid (TTA) from the time of clipping or after hypertension was established. TTA treatment attenuated the development of hypertension and reduced established 2K1C hypertension. The mRNA level of renin in the clipped kidney and the plasma renin activity were markedly reduced, and the plasma angiotensin II level tended to decrease after TTA treatment. In addition, TTA reduced the mRNA level of angiotensinogen in white adipose tissue. Prevention of organ damage was demonstrated by normal urinary excretion of protein, maintained serum albumin, lower heart weight, and clearly reduced vascular, glomerular, and tubulointerstitial damage in the nonclipped kidney. Renal function was not affected as estimated by unchanged plasma creatinine. Furthermore, the serum levels of triacylglycerol and cholesterol were reduced by TTA. The serum fatty acid composition was changed, resulting in a favorable increase of oleic acid. However, the levels of all of the omega-3 fatty acids and of linoleic acid were reduced, and no change was seen in the level of arachidonic acid, but the urinary excretion of 8-iso-prostaglandin F2alpha was declined. In conclusion, TTA attenuated the development of hypertension, reduced established hypertension, and prevented the development of organ damage in 2K1C rats, possibly by reducing the amounts of the vasoconstrictors angiotensin II and 8-iso-prostaglandin F2alpha and by inducing a favorable increase of oleic acid in serum.

Antihypertensive effect of ragaglitazar: A novel PPARα and γ dual activator

Ragaglitazar is a novel and potent dual peroxisome proliferators activated receptor (PPAR) α and γ activator. The aim of this study is to investigate the effect of ragaglitazar on blood pressure and endothelial function in insulin resistant animal model and non-insulin resistant hypertensive models. The effects ragaglitazar were tested in Zucker fa/fa, spontaneously hypertensive rats (SHR), 2 kidney 1clip rat (2K1C) and Wistar Kyoto rats (WKY). Pioglitazone was taken as a comparative standard. Ragaglitazar showed significant reduction ( P < 0.001) of systolic blood pressure (SBP) in insulin resistant fa/fa rats, with concomitant reduction in plasma triglycerides (TG) and insulin levels while pioglitazone (10 mg kg −1) showed significant ( P < 0.05) but comparatively less reduction. Ragaglitazar in contrast to pioglitazone showed significant reduction ( P < 0.05) of SBP in SHR, 2K1C while the same dose did not have any effect on normotensive WKY. Ragaglitazar also showed significant improvement in acetylcholine-induced relaxation in isolated aorta of Zucker fa/fa, SHR, 2K1C and also potentiated the insulin-induced vasorelaxation in Zucker fa/fa rats. These findings summarize that ragaglitazar shows significant reduction of BP and improvement in endothelial function not only in insulin resistant but also in non-insulin resistant hypertensive models where standard thiazolidinediones are ineffective. These data indicates that dual PPARα and γ activator ragaglitazar can be beneficial for the treatment of hypertension and vascular disease commonly associated with type 2 diabetes.

Regeneration of optic nerve fibers following graded injuries in rats

To investigate the changes of retinal ganglion cell (RGC) and their axons, and nerve regeneration ability following graded optic nerve injury (ONI) in rats. A pair of cross-action forceps with 148.0 g clipping pressure was used to clip rat optic nerves for 3, 6, 12, 30 and 60 s to induce graded ONI animal model. The RGC was counted at 0.5, 1, 2, 3 and 7 months and the axons were observed 1, 2 and 3 months post-injury. The regeneration process was observed by transmission electron microscopy. The number of optic nerve fibers in transverse sections was calculated in silver-stained longitudinal sections, and a regeneration index (RI) was calculated based on these numbers. The RI, reflecting the regeneration ability of injured optic nerves, was calculated as follows: (number of nerve fibers 0.5 mm behind injury site-number of nerve fibers 2.5 mm behind injury site)/(number of nerve fibers 0.5 mm retrobulbarly-number of nerve fibers 2.5 mm behind injury site). RGC and axons lost continuously after partial ONI. The loss of RGC was fitted with exponential pattern consisted of two phases, acute losing phase within first two weeks post injury and followed by another phase characterized by slowly reducing of RGC. The loss ratio of RGC increased and the survival ratio decreased with the severity of injury intensity. The loss of RGC and axons was aggregated in severe injury and showed a self-limited trend in mild injury. A large amount of clustered, zonal unmyelinated regeneration fibers were present after injury. The RI was 1.409, 1.490, 0.916, 1.119 and 1.224 following 3, 6, 12, 30 and 60 s clipping injury (chi2 = 281.2, P < 0.01), respectively. Different RI was associated to different injury intensity, with a greater regeneration ability in mild injury. The secondary reaction and regeneration ability vary with graded intensity of optic nerve injury. A self-limited secondary reaction and a more powerful regeneration ability are associated with a mild injury. The repair behavior and the injury may reach a balance and result in a successful regeneration after a certain degree of injury.

Potential of Gene Therapy Strategy for the Treatment of Hypertension

Hypertension is one of the most important risk factors for cardiovascular diseases (CVDs). CVD extends across all populations and represents the leading cause of morbidity and mortality in industrialized countries. Hypertension increases the risk of peripheral arterial disease, cardiomyopathy, stroke, and renal failure. The disease affects &50 million Americans and goes undetected in at least one third of the population. In spite of the tremendous progress made by pharmacotherapy in the management and control of hypertension, there has been a steady escalation in its prevalence during the last decade. This has led many to conclude that traditional pharmacotherapy has reached an intellectual plateau and that novel and innovative approaches must be sought for the treatment, control, and possible cure of hypertension. As a result, efforts of our group and those of many others have been diverted to explore the use of gene transfer and gene therapy strategies for a long-term control of hypertension. We have argued that gene therapy offers potentially significant improvements and benefits over the use of traditional pharmacotherapy: (1) noncompliance by patients can be significantly reduced or even eliminated because of the fact that a single treatment involving gene transfer could remain effective for months or even years; (2) side effects associated with pharmacotherapy can be minimized as a result of specific targeting of a therapeutic gene in a given tissue and optimally influencing cardiovascular pathophysiology on an individual patient basis; and (3) with its potential to produce long-term beneficial outcomes in end-organ damage, the gene therapy strategy could lead to a cure of hypertension and its related pathophysiology. It is noteworthy to mention that current pharmacotherapies are often unable to reverse end-organ damage associated with hypertension. In order for the gene therapy for hypertension to be successful, one must provide conceptual support of its efficacy in …

Characteristics of the renal C-type natriuretic peptide receptor in hypertrophied and developing rat kidney

This study investigates the effect of hypertrophy, using one kidney and one kidney/one clip rats, and development, comparing 3- and 12-week-old rats, on the expression of the 28-amino acid atrial natriuretic peptide (ANP(1-28)) binding sites in rat kidney. Here we report an increased B(max) value of glomerular binding sites for ANP(1-28) and C-type natriuretic peptide 1-22 (CNP(1-22)) in hypertrophied and developing kidney, without modifying their affinity, an effect that was prevented in the presence of the synthetic des[Gln(18), Ser(19), Gly(20), Leu(21), Gly(22)]ANP(4-23)-amide (C-ANF), suggesting that natriuretic peptide receptor (NPR)-C binding sites might be enhanced. The enhanced B(max) was only detected in the high affinity binding site for CNP(1-22), which has been identified as the 67 kDa NPR-C-like protein. A similar effect was observed in renal glomeruli from 3-week-old rats compared with 12-week-old rats. Our results indicate that ANP(1-28), CNP(1-22) and C-ANF inhibited cAMP synthesis stimulated by the physiological agonists histamine and 5-hydroxytryptamine or directly by forskolin. The inhibitory effect was found to be significantly greater in 1-kidney and 1-kidney/1-clip rats than in controls, and in 3-week-old rats compared with 12-week-old rats. Our observations suggest that this effect must be attributed to the 67 kDa NPR-C-like protein due to the enhanced B(max) values and the reported inhibitory role for this receptor on adenylyl cyclase activity. The enhanced inhibitory role of natriuretic peptides on cAMP synthesis in hypertrophied and developing kidney may influence glomerular function in the rat kidney and suggests a role for the 67 kDa NPR-C-like protein in growth.

Ketamine-induced changes in metabolic and endocrine parameters of normal and 2-kidney 1-clip rats

The aim of this study was to investigate the effect of ketamine on the endocrine and lipid metabolic status of the renal-banded animals. Forty male rats were randomly divided into four groups. Group A served as control, Group B animals received ketamine intraperitoneally at a dose of 100 mg kg(-1), Group C was submitted to 2-kidney 1-clip experimental hypertension and Group D received ketamine as above, as well as being submitted to renal artery clipping. Atrial natriuretic peptide, angiotensin II and free fatty acid concentrations were measured in serum. In addition, adipose tissue lipoprotein lipase activity and angiotensin II content were determined, while the left ventricular weight relative to body weight was used as a cardiac hypertrophy index. In renal-banded rats (Groups C and D) serum atrial natriuretic peptide, free fatty acid and angiotensin II concentrations as well as ventricular weight were increased, while adipose tissue lipoprotein lipase activity was lower than in control animals (Groups A and B). Ketamine administration did not influence angiotensin II concentrations either in normal (Group B) or banded rats (Group D). Ketamine increased serum atrial natriuretic peptide and free fatty acid concentrations only in normal animals (Group B). It had no influence on adipose tissue lipoprotein lipase activity either in normal (Group B) or banded animals (Group D). Adipose angiotensin II content did not differ between the four groups. Ketamine increased the atrial natriuretic peptide and free fatty acid concentration in normal rats. In 2-kidney 1-clip animals, ketamine did not elicit an additional response of serum atrial natriuretic peptide or free fatty acids levels. Its contribution to these factors was not significant.

L-Glutamine Metabolism Is Not A Major Source Of Increased Free Radical Generation In Goldblatt Renovascular Hypertension

Glutamine has been implicated in the generation of free radicals and free radicals-induced impairment of vascular responses to nitrovasodilators may underlie the pathogenesis of vasospasm in 2K-1C hypertension. Plasma glutamine levels were therefore determined in 2K-1C and 1K-1C hypertensive rats in order to ascertain the direction of change of this amino acid in this model of renovascular hypertension. Hypertension was induced in male SD rats (99±2.3 g) by subjecting them to left renal artery clamping using a 0.2mm silver clip (2K-1C, n=7) under ether anesthesia. Control rats (n=7) were sham-operated (Sh-Op). Rats with 1K-1C hypertension (n=8) and uni-nephrectomized controls (1K:, n=8), additionally underwent right nephrectomy. 10 weeks (2K-1C) and 4 weeks (1K-1C) respectively after renal artery clamping, clipped rats exhibited elevated blood pressures (P Key words: Glutamine, Glutamate, Superoxide Radicals, Experimental Renovascular Hypertension Nigerian Journal of Physiological Sciences Vol.18(1-2) 2003: 11-17

Foreword

Abstract : Warm- and cold-acclimated rats could withstand prolonged exposure to cold after restriction of food. Their catecholamine excretion rapidly attained maximal values and the animals died in hypothermia. The same happened with warm-acclimated rats whose insulation had been reduced by removal of the fur. Cold-acclimated clipped rats survived in the cold, but their catecholamine response was much more intense than that of intact cold-acclimated animals. These two series of experiments strongly support the view that acclimation to cold is limited by the finite capacity of the organism to produce and/or secrete sufficient amounts of catecholamines to maintain thermal balance. They also emphasize the necessity for coldacclimated animals to reach a new level of acclimation when conditions are changed. The previous degree of acclimation increases the chances to attain that new state of equilibrium by virture of an increased sensitivity of cold-acclimated rats to catecholamines, thus extending the time at which the catecholamine production and/or secretion becomes saturated. The importance of adrenaline as a supplementary hormone of defense against cold is shown by the lower ability of adrenalectomized corticoids maintained rats to support cold exposure under severe conditions. (Author)

N-domain angiotensin I-converting enzyme with 80 kDa as a possible genetic marker of hypertension.

We have previously described angiotensin I-converting enzyme (ACE) forms in urine of normotensive (190 and 65 kDa) and hypertensive patients (90 and 65 kDa, N-domain ACEs). Based on the results described above, experimental and genetic models of hypertension were investigated to distinguish hemodynamic and genetic influence on the generation of ACE profile in urine: Wistar-Kyoto and Brown Norway rats (WKY and BN), spontaneously and stroke-prone spontaneously hypertensive rats (SHR and SHR-SP), one kidney/one clip rats (1K1C), deoxycorticosterone acetate (DOCA) salt-treated and untreated rats, and enalapril-treated SHR (SHRen). Two peaks with ACE activity were separated from the urine of WKY and BN rats submitted to an AcA-44 column, WK-1/BN-1 (190 kDa), and WK-2/BN-2 (65 kDa), as described for urine of normotensive subjects. The same results were obtained for urine of 1K1C and DOCA salt-treated and untreated rats, analyzed to evaluate the influence of hemodynamic factors in the ACE profile in urine. The urine from SHR, SHR-SP, and SHRen presented 80 (S-1, SP-1, Sen-1) and 65 (S-2, SP-2, Sen-2) kDa ACE forms, differing from the urine profile of normotensive rats, but similar to that described for hypertensive patients. The presence of 80 kDa ACE in urine of SHR, SHR-SP, and SHRen and its absence in urine of experimental hypertensive rats (1K1C and DOCA salt) support the hypothesis that this enzyme could be a possible genetic marker of hypertension. Taken together, our results provide evidence that ACE forms with 90/80 kDa isolated from the urine of hypertensive subjects and genetic hypertensive animals behaves as a possible genetic marker of hypertension and not as a marker of high blood pressure.

Increase in adrenomedullin gene expression in the left atrium and ventricle in the two-kidney one-clip renovascular hypertensive rats

The 2-kidney 1-clip rat model was set up by clipping the left renal artery. At 5 weeks after clipping, there was an increase in preproadrenomedullin mRNA levels in both the left atria and the left ventricle. Adrenomedullin (AM) contents, however, increased in the left ventricle but decreased in the left atrium. These changes were not observed at 2 weeks after clipping. There were no changes in AM or preproadrenomedullin mRNA levels in the thoracic aorta and the mesenteric artery, and in plasma AM levels at 2 weeks or 5 weeks after clipping. We concluded that there was an increase in the secretion of AM in the left ventricle and the left atria in the 5 week renovascular hypertensive rat. The lack of change in plasma AM level suggests a paracrine function for the peptide in this setting.

A membrane potential-sensitive dye for vascular smooth muscle cells assays

Changes in membrane potential of rat aorta smooth muscle cells were investigated using the bis-oxonol sensitive probe DIBAC 2(3). We compared the changes in membrane potential induced by a high external KCl concentration in aorta smooth muscle cells from normotensive 2 kidney (2K) and from renal hypertensive 2 kidney-1 clip (2K-1C) rats. The spectral properties of the membrane potential were first characterized in aqueous buffers and in cultured smooth muscle cells from 2K and 2K-1C rat aortas. Fluorescence emission and the images were recorded using a laser scanning confocal microscope. The relationship between fluorescence intensity (FI) and membrane potential ( ψ m) as a function of the increasing extracellular KCl concentration was linear in the 5–40 mmol/L KCl range in both 2K and 2K-1C rat aorta cells. Cell membranes from 2K-1C rat aorta cells were more depolarized (−55 mV) than 2K rat aorta cells (−65 mV). The results show that in 2K-1C aorta cells only 10 mmol/L KCl was needed to induce complete membrane depolarization while in 2K cells 40 mmol/L KCl was needed to induce a similar effect. This study clearly shows that the method is suitable to measure the membrane potential in cultured smooth muscle cells.

Angiotensin II type 1 receptor blockade prevents lethal malignant hypertension: relation to kidney inflammation.

Angiotensin II is elevated in malignant hypertension. We tested the hypothesis that angiotensin II type 1 receptor blockade can prevent the development of malignant hypertension even in the absence of a blood pressure-lowering effect. Two-kidney, 1-clip rats were followed up for 28 days; blood pressure was measured by tail-cuff plethysmography and intra-arterially. After a 2-week run-in phase, rats received valsartan at a dose of 0.3 (n=14) or 3 (n=12) mg. kg(-1). d(-1) or solvent (n=27). Only the higher dose of valsartan, but not the lower dose, decreased blood pressure. Both doses of valsartan prevented the development of lethal malignant hypertension. Twenty of 27 solvent-treated renovascular hypertensive rats died, but only 3 of 14 rats treated with the low dose and 1 of 12 rats treated with the high dose of valsartan died. Histological signs of malignant nephrosclerosis were found in all rats examined that had died throughout the study and in 6 of 7 surviving solvent-treated renovascular hypertensive animals. Increased expression of monocyte chemoattractant protein-1 and prominent interstitial influx of macrophages occurred in the nonclipped kidneys exposed to high pressure in solvent-treated rats. These alterations were prevented by valsartan at both doses, irrespective of blood pressure effects. Angiotensin II type 1 receptor blockade by valsartan prevents lethal malignant hypertension independently of blood pressure. The results suggest that reduction of angiotensin-induced inflammation in the kidney may contribute to the protective effects of valsartan.

Role of angiotensin II and free radicals in blood pressure regulation in a rat model of renal hypertension.

One-kidney, 1-clip rats (1K1C) or uninephrectomized controls were treated with either the superoxide dismutase mimetic tempol (0.5 mmol. kg(-1). d(-1)), angiotension type 1 receptor inhibitor losartan (50 mmol. L(-1). kg(-1). d(-1)), or both (n=6 per group) for 2 weeks. At the end of the study, systolic blood pressure (BP) decreased on average by 21% in tempol-treated and 29% in losartan-treated versus untreated 1K1C (217+/-4.4 mm Hg) and was normalized in the losartan plus tempol group. Mean BP also decreased from 159+/-3.7 mm Hg in 1K1C to 93+/-2.8 mm Hg in the losartan plus tempol group. Also, aortic wall area was reduced by 18% in losartan- or tempol-treated 1K1C and by 30% in losartan plus tempol rats compared with untreated 1K1C. Plasma renin activity was increased from 4.8+/-0.3 in untreated 1K1C to 15.9+/-0.9 ng. mL(-1). h(-1) in losartan-treated but not tempol-treated 1K1C. Superoxide generation by the isolated aortic rings assessed by lucigenin chemiluminescence was significantly decreased (by approximately 40%) in all losartan, tempol, and losartan plus tempol groups compared with untreated 1K1C. Nitrotyrosine ELISA in the kidney displayed a significant reduction, from 59+/-13 ng/mg of protein in 1K1C to 12.5+/-5 ng/mg of protein in the losartan plus tempol 1K1C. Western blotting for nNOS in kidney cortex and medulla showed a protein increase in both fractions of 1K1C versus controls and was normalized by losartan plus tempol treatment. Collectively, data show a synergistic effect of losartan and tempol on BP reduction in 1K1C rats. The mechanism may involve reduced superoxide production and nitrotyrosine formation in kidney and decreased kidney neuronal-type NO synthase expression in treated animals. This status in the oxidative balance seems to affect BP in the renal hypertensive rats.

Modulation of cardiac natriuretic peptide gene expression following endothelin type A receptor blockade in renovascular hypertension.

Increased expression of the cardiac natriuretic peptides (NP), atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) is observed during chronic hemodynamic overload. The mechanisms underlying this process are not fully understood. In vitro, endothelin 1 (ET-1) is a powerful stimulator of cardiac NP and, therefore, has been assumed to be one possible mediator of increased NP gene expression following chronic pressure or volume overload. In the present work we investigated the possible role of ET-1 in mediating the observed upregulation of cardiac NP in two kidney-one clip (2K-1C) Goldblatt hypertensive rats treated for 6 weeks with the ET-1 type A (ET(A)) receptor subtype receptor antagonist ABT-627. 2K-1C hypertension was induced in male Sprague-Dawley rats weighing 100-125 g by placing a silver clip (internal diameter 0.25 mm) around the left renal artery through a flank incision. The right kidney was left undisturbed. Sham operated rats underwent the same experimental procedures but no clip was placed on the left renal artery. ABT-627 was administered (10 mg/kg per day) in the drinking water for 6 weeks. In hypertensive rats, ABT-627 prevented a further rise in blood pressure beginning at 3 weeks after clipping and reduced the ventricular hypertrophy observed at the end of the experiment. ET(A) blockade prevented enhanced NP gene expression in the right ventricle and partially prevented it in the left ventricle. No modifications in atrial NP gene expression were observed in either control or 2K-1C animals. ET(A) blockade decreased BNP circulating levels but did not affect ANF plasma levels in clipped rats. ABT-627 increased alpha-myosin heavy chain gene expression and decreased the abundance of the beta isoform transcript. The results obtained in the present investigation show the participation of ET-1 in the increased expression of ventricular NP in 2K-1C renovascular hypertension and an apparent lack of effect of ET(A) blockade on atrial NP gene expression in both control and hypertensive animals thus showing that in vivo, atrial and ventricular NP gene expression are differentially regulated.

Rat Coronary Endothelial Cell Membrane Potential Responses During Hypertension.

-The purpose of this study was to provide the first membrane potential profile in coronary endothelial cells from normotensive sham-operated control and 1-kidney, 1-clip renal hypertensive rats. Dilator responses were assessed in cannulated coronary arteries from control and 1-kidney, 1-clip rats, and the perforated patch-clamp method was used to compare membrane potential responses between the intact endothelial cells. Under these conditions, acetylcholine (100 pmol/L to 10 µmol/L) induced similar large dilations of coronary arteries from control and 1-kidney, 1-clip rats that were associated with endothelial cell hyperpolarizing responses of 16+/-3 and 18+/-2 mV, respectively. Substance P (10 fmol/L to 1 nmol/L) and bradykinin (100 fmol/L to 10 nmol/L) also substantially dilated coronary arteries from control rats but only induced small (2 to 4 mV) endothelial cell hyperpolarizing responses. These dilations, which appeared independent of membrane potential changes, were highly blunted or absent in arteries from 1-kidney, 1-clip rats. Thus, dilator responses to acetylcholine that are associated with large endothelial hyperpolarizing responses are normal in the small coronary arteries of 1-kidney, 1-clip rats. However, dilator response to substance P and bradykinin, which apparently are not heavily dependent on endothelial cell hyperpolarizations, are selectively targeted for impairment in the coronary arteries of this model of hypertension