Chronic kidney disease with comorbid cardiac dysfunction exacerbates cardiac and renal damage

To address the pathophysiological mechanisms underlying chronic kidney disease with comorbid cardiac dysfunction, we investigated renal and cardiac, functional and structural damage when myocardial infarction (MI) was applied in the setting of kidney injury (induced by 5/6 nephrectomy—STNx). STNx or Sham surgery was induced in male Sprague–Dawley rats with MI or Sham surgery performed 4 weeks later. Rats were maintained for a further 8 weeks. Rats (n = 36) were randomized into four groups: Sham+Sham, Sham+MI, STNx+Sham and STNx+MI. Increased renal tubulointerstitial fibrosis (P < 0.01) and kidney injury molecule‐1 expression (P < 0.01) was observed in STNx+MI compared to STNx+Sham animals, while there were no further reductions in renal function. Heart weight was increased in STNx+MI compared to STNx+Sham or Sham+MI animals (P < 0.05), despite no difference in blood pressure. STNx+MI rats demonstrated greater cardiomyocyte cross‐sectional area and increased cardiac interstitial fibrosis compared to either STNx+Sham (P < 0.01) or Sham+MI (P < 0.01) animals which was accompanied by an increase in diastolic dysfunction. These changes were associated with increases in ANP, cTGF and collagen I gene expression and phospho‐p38 MAPK and phospho‐p44/42 MAPK protein expression in the left ventricle. Addition of MI accelerated STNx‐induced structural damage but failed to significantly exacerbate renal dysfunction. These findings highlight the bidirectional response in this model known to occur in cardiorenal syndrome (CRS) and provide a useful model for examining potential therapies for CRS.     

Effect of combining an ACE inhibitor and a VDR activator on glomerulosclerosis, proteinuria, and renal oxidative stress in uremic rats

Angiotensin-converting enzyme (ACE) inhibitors ameliorate the progression of renal disease. In combination with vitamin D receptor activators, they provide additional benefits. In the present study, uremic (U) rats were treated as follows: U+vehicle (UC), U+enalapril (UE; 25 mg/l in drinking water), U+paricalcitol (UP; 0.8 μg/kg ip, 3 × wk), or U+enalapril+paricalcitol (UEP). Despite hypertension in UP rats, proteinuria decreased by 32% vs. UC rats. Enalapril alone, or in combination with paricalcitol, further decreased proteinuria (≈70%). Glomerulosclerosis and interstitial infiltration increased in UC rats. Paricalcitol and enalapril inhibited this. The increase in cardiac atrial natriuretic peptide (ANP) seen in UC rats was significantly decreased by paricalcitol. Enalapril produced a more dramatic reduction in ANP. Renal oxidative stress plays a critical role in inflammation and progression of sclerosis. The marked increase in p22(phox), a subunit of NADPH oxidase, and decrease in endothelial nitric oxide synthase were inhibited in all treated groups. Cotreatment with both compounds inhibited the uremia-induced increase in proinflammatory inducible nitric oxide synthase (iNOS) and glutathione peroxidase activity better than either compound alone. Glutathione reductase was also increased in UE and UP rats vs. UC. Kidney 4-hydroxynonenal was significantly increased in the UC group compared with the normal group. Combined treatment with both compounds significantly blunted this increase, P < 0.05, while either compound alone had no effect. Additionally, the expression of Mn-SOD was increased and CuZn-SOD decreased by uremia. This was ameliorated in all treatment groups. Cotreatment with enalapril and paricalcitol had an additive effect in increasing CuZn-SOD expression. In conclusion, like enalapril, paricalcitol alone can improve proteinuria, glomerulosclerosis, and interstitial infiltration and reduce renal oxidative stress. The effects of paricalcitol may be amplified when an ACE inhibitor is added since cotreatment with both compounds seems to have an additive effect on ameliorating uremia-induced changes in iNOS and CuZn-SOD expression, peroxidase activity, and renal histomorphometry.     

Renalase attenuates hypertension,renal injury and cardiac remodelling in rats with subtotal nephrectomy

Chronic kidney disease is associated with higher risk of cardiovascular complication and this interaction can lead to accelerated dysfunction in both organs. Renalase, a kidney‐derived cytokine, not only protects against various renal diseases but also exerts cardio‐protective effects. Here, we investigated the role of renalase in the progression of cardiorenal syndrome (CRS) after subtotal nephrectomy. Sprague–Dawley rats were randomly subjected to sham operation or subtotal (5/6) nephrectomy (STNx). Two weeks after surgery, sham rats were intravenously injected with Hanks' balanced salt solution (sham), and STNx rats were randomly intravenously injected with adenovirus‐β‐gal (STNx+Ad‐β‐gal) or adenovirus‐renalase (STNx+Ad‐renalase) respectively. After 4 weeks of therapy, Ad‐renalase administration significantly restored plasma, kidney and heart renalase expression levels in STNx rats. We noticed that STNx rats receiving Ad‐renalase exhibited reduced proteinuria, glomerular hypertrophy and interstitial fibrosis after renal ablation compared with STNx rats receiving Ad‐β‐gal; these changes were associated with significant decreased expression of genes for fibrosis markers, proinflammatory cytokines and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase components. At the same time, systemic delivery of renalase attenuated hypertension, cardiomyocytes hypertrophy and cardiac interstitial fibrosis; prevented cardiac remodelling through inhibition of pro‐fibrotic genes expression and phosphorylation of extracellular signal‐regulated kinase (ERK)‐1/2. In summary, these results indicate that renalase protects against renal injury and cardiac remodelling after subtotal nephrectomy via inhibiting inflammation, oxidative stress and phosphorylation of ERK‐1/2. Renalase shows potential as a therapeutic target for the prevention and treatment of CRS in patients with chronic kidney disease.     

Renal failure induces telomere shortening in the rat heart

BackgroundRenal failure aggravates pathological cardiac remodelling induced by myocardial infarction (MI). Cardiac remodelling is associated with telomere shortening, a marker for biological ageing. We investigated whether mild and severe renal failure shorten cardiac telomeres and excessively shorten telomeres after MI. MethodsRats were subjected to sham, unilateral (UNX) or 5/6th nephrectomy (5/6NX) to induce none, mild or severe renal failure. MI was induced by left coronary artery ligation. Renal function parameters and blood pressure were measured. DNA was isolated from non-infarcted cardiac tissue. Telomere length was assessed by quantitative polymerase chain reaction (PCR). ResultsProteinuria was unchanged in UNX and MI compared with control, but strongly increased in 5/6NX, UNX+MI and 5/6NX+MI. Serum creatinine levels were increased fourfold in 5/6NX and tenfold in 5/6NX+MI. 5/6NX and groups with both renal failure and MI showed an approximate 20% reduction of telomere length, similar to the MI group. No excess telomere shortening was observed in hearts from rats with renal ablation after MI. ConclusionSevere renal failure, but not mild renal failure, leads to shortening of cardiac telomeres to a similar extent as found after MI. Renal failure did not induce excessive telomere shortening after MI. (Neth Heart J 2009;17:190–4.)     

Regulation of components of the brain and cardiac renin-angiotensin systems by 17beta-estradiol after myocardial infarction in female rats

The present study tested the hypothesis that 17beta-estradiol (E2) inhibits increases in angiotensin-converting enzyme (ACE) and ANG II type 1 receptor (AT1R) in the brain and heart after myocardial infarction (MI) and, thereby, inhibits development of left ventricular (LV) dysfunction after MI. Age-matched female Wistar rats were treated as follows: 1) no surgery (ovary intact), 2) ovariectomy + subcutaneous vehicle treatment (OVX + Veh), or 3) OVX + subcutaneous administration of a high dose of E2 (OVX + high-E2). After 2 wk, rats were randomly assigned to coronary artery ligation (MI) and sham operation groups and studied after 3 wk. E2 status did not affect LV function in sham rats. At 2-3 wk after MI, impairment of LV function was similar across MI groups, as measured by echocardiography and direct LV catheterization. LV ACE mRNA abundance and activity were increased severalfold in all MI groups compared with respective sham animals and to similar levels across MI groups. In most brain nuclei, ACE and AT1R densities increased after MI. Unexpectedly, compared with the respective sham groups the relative increase was clearest (20-40%) in OVX + high-E2 MI rats, somewhat less (10-15%) in ovary-intact MI rats, and least (< 10-15%) in OVX + Veh MI rats. However, because in the sham group brain ACE and AT1R densities increased in the OVX + Veh rats and decreased in the OVX + high-E2 rats compared with the ovary-intact rats, actual ACE and AT1R densities in most brain nuclei were modestly higher (< 20%) in OVX + Veh MI rats than in the other two MI groups. Thus E2 does not inhibit upregulation of ACE in the LV after MI and amplifies the percent increases in ACE and AT1R densities in brain nuclei after MI, despite E2-induced downregulation in sham rats. Consistent with these minor variations in the tissue renin-angiotensin system, during the initial post-MI phase, E2 appears not to enhance or hinder the development of LV dysfunction.     

Regression of Glomerular and Tubulointerstitial Injuries by Dietary Salt Reduction with Combination Therapy of Angiotensin II Receptor Blocker and Calcium Channel Blocker in Dahl Salt-Sensitive Rats

A growing body of evidence indicates that renal tissue injuries are reversible. We investigated whether dietary salt reduction with the combination therapy of angiotensin II type 1 receptor blocker (ARB) plus calcium channel blocker (CCB) reverses renal tissue injury in Dahl salt-sensitive (DSS) hypertensive rats. DSS rats were fed a high-salt diet (HS; 4% NaCl) for 4 weeks. Then, DSS rats were given one of the following for 10 weeks: HS diet; normal-salt diet (NS; 0.5% NaCl), NS + an ARB (olmesartan, 10 mg/kg/day), NS + a CCB (azelnidipine, 3 mg/kg/day), NS + olmesartan + azelnidipine or NS + hydralazine (50 mg/kg/day). Four weeks of treatment with HS diet induced hypertension, proteinuria, glomerular sclerosis and hypertrophy, glomerular podocyte injury, and tubulointerstitial fibrosis in DSS rats. A continued HS diet progressed hypertension, proteinuria and renal tissue injury, which was associated with inflammatory cell infiltration and increased proinflammatory cytokine mRNA levels, NADPH oxidase activity and NADPH oxidase-dependent superoxide production in the kidney. In contrast, switching to NS halted the progression of hypertension, renal glomerular and tubular injuries. Dietary salt reduction with ARB or with CCB treatment further reduced blood pressure and partially reversed renal tissues injury. Furthermore, dietary salt reduction with the combination of ARB plus CCB elicited a strong recovery from HS-induced renal tissue injury including the attenuation of inflammation and oxidative stress. These data support the hypothesis that dietary salt reduction with combination therapy of an ARB plus CCB restores glomerular and tubulointerstitial injury in DSS rats.     

Reduction of heart rate by chronic beta1-adrenoceptor blockade promotes growth of arterioles and preserves coronary perfusion reserve in postinfarcted heart

Adequate growth of coronary vasculature in the remaining left ventricular (LV) myocardium after myocardial infarction (post-MI) is a crucial factor for myocyte survival and performance. We previously demonstrated that post-MI coronary angiogenesis can be stimulated by bradycardia induced with the ATP-sensitive K(+) channel antagonist alinidine. In this study, we tested the hypothesis that heart rate reduction with beta-blockade may also induce coronary growth in the post-MI heart. Transmural MI was induced in 12-mo-old male Sprague-Dawley rats by occlusion of the left anterior descending coronary artery. Bradycardia was induced by administration of the beta-adrenoceptor blocker atenolol (AT) via drinking water (30 mg/day). Three groups of rats were compared: 1) control/sham (C/SH), 2) MI, and 3) MI + AT. In the MI + AT rats, heart rate was consistently reduced by 25-28% compared with C/SH rats. At 4 wk after left anterior descending coronary ligation, infarct size was similar in MI and MI + AT rats (67.1 and 61.5%, respectively), whereas a greater ventricular hypertrophy occurred in bradycardic rats, as indicated by a higher ventricular weight-to-body weight ratio (3.4 +/- 0.1 vs. 2.8 +/- 0.1 mg/g in MI rats). Analysis of LV function revealed a smaller drop in ejection fraction in the MI + AT than in the MI group ( approximately 24 vs. approximately 35%). Furthermore, in MI + AT rats, maximal coronary conductance and coronary perfusion reserve were significantly improved compared with the MI group. The better myocardial perfusion indexes in MI + AT rats were associated with a greater increase in arteriolar length density than in the MI group. Thus chronic reduction of heart rate induced with beta-selective blockade promotes growth of coronary arterioles and, thereby, facilitates regional myocardial perfusion in post-MI hearts.     

NO and cGMP mediate angiotensin AT2 receptor-induced renal renin inhibition in young rats

We hypothesized that angiotensin subtype-2 receptor (AT(2)R) inhibits renal renin biosynthesis in young rats via nitric oxide (NO). We monitored changes in renal NO, cGMP, renal renin content (RRC), and ANG II in 4-wk-old rats in response to low sodium (LNa(+)) intake alone and combined with 8-h direct renal cortical administration of AT(1) receptor blocker valsartan (VAL), AT(2)R blocker PD123319 (PD), NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME), NO donor S-nitroso-N-acetyl penicillamine (SNAP), or guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo[4,2-alpha] quinoxaline-1-one (ODQ). In addition, we monitored renal endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) in response to VAL or PD. LNa(+), VAL, PD, l-NAME, and ODQ increased RRC, ANG II, and renin mRNA. PD and l-NAME decreased NO and cGMP, while SNAP reduced RRC, ANG II, renin mRNA, and reversed the effects of PD. PD also reduced eNOS and nNOS protein and mRNA. Combined treatment with PD, l-NAME, or ODQ and VAL reversed the effects of VAL and caused further increase in RRC, ANG II, renin mRNA, and protein. ODQ reversed the effects of SNAP. These data demonstrate that the renal AT(2) receptor decreases renal renin biosynthesis and ANG II production in young rats. Reversal of the PD effects by SNAP and SNAP effects by ODQ confirms that NO and cGMP mediate the AT(2) receptor inhibition of renal renin production.     

Preconditioning via Angiotensin Type 2 Receptor Activation Improves Therapeutic Efficacy of Bone Marrow Mononuclear Cells for Cardiac Repair

Background

The therapeutic efficiency of bone marrow mononuclear cells (BMMNCs) autologous transplantation for myocardial infarction (MI) remains low. Here we developed a novel strategy to improve cardiac repair by preconditioning BMMNCs via angiotensin II type 2 receptor (AT2R) stimulation.

Methods and Results

Acute MI in rats led to a significant increase of AT2R expression in BMMNCs. Preconditioning of BMMNCs via AT2R stimulation directly with an AT2R agonist CGP42112A or indirectly with angiotensin II plus AT1R antagonist valsartan led to ERK activation and increased eNOS expression as well as subsequent nitric oxide generation, ultimately improved cardiomyocyte protection in vitro as measured by co-culture approach. Intramyocardial transplantation of BMMNCs preconditioned via AT2R stimulation improved survival of transplanted cells in ischemic region of heart tissue and reduced cardiomyocyte apoptosis and inflammation at 3 days after MI. At 4 weeks after transplantation, compared to DMEM and non-preconditioned BMMNCs group, AT2R stimulated BMMNCs group showed enhanced vessel density in peri-infarct region and attenuated infarct size, leading to global heart function improvement.

Conclusions

Preconditioning of BMMNCs via AT2R stimulation exerts protective effect against MI. Stimulation of AT2R in BMMNCs may provide a new strategy to improving therapeutic efficiency of stem cells for post MI cardiac repair.     

AT1 receptor-mediated augmentation of angiotensinogen, oxidative stress, and inflammation in ANG II-salt hypertension

Augmentation of intrarenal angiotensinogen (AGT) synthesis, secretion, and excretion is associated with the development of hypertension, renal oxidative stress, and tissue injury during ANG II-dependent hypertension. High salt (HS) exacerbates hypertension and kidney injury, but the mechanisms remain unclear. In this study, we determined the consequences of HS intake alone compared with chronic ANG II infusion and combined HS plus ANG II on the stimulation of urinary AGT (uAGT), renal oxidative stress, and renal injury markers. Sprague-Dawley rats were subjected to 1) a normal-salt diet [NS, n = 5]; 2) HS diet [8% NaCl, n = 5]; 3) ANG II infusion in NS rats [ANG II 80 ng/min, n = 5]; 4) ANG II infusion in HS rats [ANG II+HS, n = 5]; and 5) ANG II infusion in HS rats treated with ANG II type 1 receptor blocker (ARB) [ANG II+HS+ARB, n = 5] for 14 days. Rats fed a HS diet alone did not show changes in systolic blood pressure (SBP), proteinuria, cell proliferation, or uAGT excretion although they did exhibit mesangial expansion, collagen deposition, and had increased NADPH oxidase activity accompanied by increased peroxynitrite formation in the kidneys. Compared with ANG II rats, the combination of ANG II infusion and a HS diet led to exacerbation in SBP (175 ± 10 vs. 221 ± 8 mmHg; P < 0.05), proteinuria (46 ± 7 vs. 127 ± 7 mg/day; P < 0.05), and uAGT (1,109 ± 70 vs.. 7,200 ± 614 ng/day; P < 0.05) associated with greater collagen deposition, mesangial expansion, interstitial cell proliferation, and macrophage infiltration. In both ANG II groups, the O(2)(-) levels were increased due to increased NADPH oxidase activity without concomitant increases in peroxynitrite formation. The responses in ANG II rats were prevented or ameliorated by ARB treatment. The results indicate that HS independently stimulates ROS formation, which may synergize with the effect of ANG II to limit peroxynitrite formation, leading to exacerbation of uAGT and greater injury during ANG II salt hypertension.     

Angiotensin type 1 receptor modulates macrophage polarization and renal injury in obesity

The mechanisms for increased risk of chronic kidney disease (CKD) in obesity remain unclear. The renin-angiotensin system is implicated in the pathogenesis of both adiposity and CKD. We investigated whether the angiotensin type 1 (AT(1)) receptor, composed of dominant AT(1a) and less expressed AT(1b) in wild-type (WT) mice, modulates development and progression of kidney injury in a high-fat diet (HFD)-induced obesity model. WT mice had increased body weight, body fat, and insulin levels and decreased adiponectin levels after 24 wk of a high-fat diet. Identically fed AT(1a) knockout (AT1aKO) mice gained weight similarly to WT mice, but had lower body fat and higher plasma cholesterol. Both obese AT1aKO and obese WT mice had increased visceral fat and kidney macrophage infiltration, with more proinflammatory M1 macrophage markers as well as increased mesangial expansion and tubular vacuolization, compared with lean mice. These abnormalities were heightened in the obese AT1aKO mice, with downregulated M2 macrophage markers and increased macrophage AT(1b) receptor. Treatment with an AT(1) receptor blocker, which affects both AT(1a) and AT(1b), abolished renal macrophage infiltration with inhibition of renal M1 and upregulation of M2 macrophage markers in obese WT mice. Our data suggest obesity accelerates kidney injury, linked to augmented inflammation in adipose and kidney tissues and a proinflammatory shift in macrophage and M1/M2 balance.     

Myocardial infarction impairs renal function, induces renal interstitial fibrosis, and increases renal KIM-1 expression: implications for cardiorenal syndrome

Progressive decline in renal function coexists with myocardial infarction (MI); however, little is known about its pathophysiology. This study aimed to systematically identify post-MI renal changes (functional, histological, and molecular) over time in a rat MI model and examine potential mechanisms that may underlie these changes. Rats were randomized into three groups: nonoperated, sham, and MI. Cardiac and renal function was assessed before death at 1, 4, 8, 12, and 16 wk with tissues collected for histological, protein, and gene studies. Tail-cuff blood pressure was lower in MI than sham and nonoperated animals only at 1 wk (P < 0.05). Systolic function was reduced (P < 0.0001) while heart/body weight and left ventricle/body weight were significantly greater in MI animals at all time points. Glomerular filtration rate decreased following MI at 1 and 4 wk (P < 0.05) but not at 8 and 12 wk and then deteriorated further at 16 wk (P = 0.052). Increased IL-6 gene and transforming growth factor (TGF)-β protein expression as well as macrophage infiltration in kidney cortex was detected at 1 wk (P < 0.05). Renal cortical interstitial fibrosis was significantly greater in MI animals from 4 wk, while TGF-β bioactivity (phospho-Smad2) was upregulated at all time points. The degree of fibrosis increased and was maximal at 16 wk. In addition, kidney injury molecule-1-positive staining in the tubules was more prominent in MI animals, maximal at 1 wk. In conclusion, renal impairment occurs early post-MI and is associated with hemodynamic and structural changes in the kidney possibly via activation of the Smad2 signaling pathway.     

NADPH oxidase contributes to renal damage and dysfunction in Dahl salt-sensitive hypertension

The goal of this study was to test the hypothesis that NADPH oxidase contributes importantly to renal cortical oxidative stress and inflammation, as well as renal damage and dysfunction, and increases in arterial pressure. Fifty-four 7- to 8-wk-old Dahl salt-sensitive (S) or R/Rapp strain rats were maintained for 5 wk on a high sodium (8%) or high sodium + apocynin (1.5 mmol/l in drinking water). Arterial and venous catheters were implanted on day 21. By day 35 in the high-Na S rats, mRNA expression of renal cortical gp91phox, p22phox, p47phox, and p67phox NADPH subunits in S rats increased markedly, and treatment of high-Na S rats with the NADPH oxidase inhibitor apocynin resulted in significant decreases in mRNA expression of these NADPH oxidase subunits. At the same time, in apocynin-treated S rats 1) renal cortical GSH/GSSG ratio increased, 2) renal cortical O2(.-) release and NADPH oxidase activity decreased, and 3) renal glomerular and interstitial damage markedly fell. Apocynin also decreased renal cortical monocyte/macrophage infiltration, and apocynin, but not the xanthine oxidase inhibitor allopurinol, attenuated decreases in renal hemodynamics and lowered arterial pressure. These data suggest that NADPH oxidase plays an important role in causing renal cortical oxidative stress and inflammation, which lead to decreases in renal hemodynamics, renal cortical damage, and increases in arterial pressure.     

Oxidative stress alters renal D1 and AT1 receptor functions and increases blood pressure in old rats

Aging is associated with an increase in oxidative stress and blood pressure (BP). Renal dopamine D1 (D1R) and angiotensin II AT1 (AT1R) receptors maintain sodium homeostasis and BP. We hypothesized that age-associated increase in oxidative stress causes altered D1R and AT1R functions and high BP in aging. To test this, adult (3 mo) and old (21 mo) Fischer 344 × Brown Norway F1 rats were supplemented without/with antioxidant tempol followed by determining oxidative stress markers (urinary antioxidant capacity, proximal tubular NADPH-gp91phox, and plasma 8-isoprostane), D1R and AT1R functions, and BP. The D1R and AT1R functions were determined by measuring diuretic and natriuretic responses to D1R agonist (SKF-38393; 1 μg·kg(-1)·min(-1) iv) and AT1R antagonist (candesartan; 10 μg/kg iv), respectively. We found that the total urinary antioxidant capacity was lower in old rats, which increased with tempol treatment. In addition, tempol decreased the elevated NADPH-gp91phox and 8-isoprostane levels in old rats. Systolic, diastolic, and mean arterial BPs were higher in old rats and were reduced by tempol. Although SKF-38393 produced diuresis in both adult and old rats, urinary sodium excretion (UNaV) increased only in adult rats. While candesartan increased diuresis and UNaV in adult and old rats, the magnitude of response was greater in old rats. Tempol treatment in old rats reduced candesartan-induced increase in diuresis and UNaV. Our results demonstrate that diminished renal D1R and exaggerated AT1R functions are associated with high BP in old rats. Furthermore, oxidative stress may cause altered renal D1R and AT1R functions and high BP in old rats.     

Blunted renal dopaminergic system activity in HgCl2-induced membranous nephropathy

The present study evaluated the possible role of the renal dopaminergic system in the sodium retention of HgCl2-induced nephrotic syndrome. The time courses of urinary excretion of sodium, protein, dopamine and the precursor l-3,4-dihydroxyphenylalanine (L-Dopa) were evaluated in HgCl2-treated and control rats up to day 21. The renal aromatic l-amino acid decarboxylase (AADC) activity, the enzyme responsible for the synthesis of renal dopamine, was evaluated during negligible proteinuria accompanied with enhanced sodium retention (day 7), increased proteinuria accompanied with greatest sodium retention (day 14) as well as during increased proteinuria accompanied with negative sodium balance (day 21). Also, the influence of volume expansion (VE, 5% bw) and the effects of the D1-like agonist fenoldopam (10 microg kg bw(-1) min(-1)) on natriuresis and on proximal tubular Na+,K+-ATPase activity were examined on day 14. The daily urinary dopamine output and urinary dopamine/L-Dopa ratios were reduced in HgCl2-treated rats from day 2 and beyond. This was accompanied by a marked decrease in renal AADC throughout the study. During VE, the fenoldopam-induced inhibition of proximal tubular Na+,K+-ATPase activity was similar between HgCl2-treated and control rats. However, the urinary sodium excretion during fenoldopam infusion was markedly increased by 60% to 120% in control rats but was not altered in HgCl2-treated rats. It is concluded that HgCl2 nephrosis is associated with a blunted renal dopaminergic system activity. However, the lack of renal dopamine in HgCl2 nephrosis does not appear to be related with the overall renal sodium retention in a state of proteinuria.     

Exercise Training Reduces Cardiac Dysfunction and Remodeling in Ovariectomized Rats Submitted to Myocardial Infarction

The aim of this study was to evaluate whether exercise training (ET) prevents or minimizes cardiac dysfunction and pathological ventricular remodeling in ovariectomized rats subjected to myocardial infarction (MI) and to examine the possible mechanisms involved in this process. Ovariectomized Wistar rats were subjected to either MI or fictitious surgery (Sham) and randomly divided into the following groups: Control, OVX+SHAM_SED, OVX+SHAM_ET, OVX+MI_SED and OVX+MI_ET. ET was performed on a motorized treadmill (5x/wk, 60 min/day, 8 weeks). Cardiac function was assessed by ventricular catheterization and Dihydroethidium fluorescence (DHE) was evaluated to analyze cardiac oxidative stress. Histological analyses were made to assess collagen deposition, myocyte hypertrophy and infarct size. Western Blotting was performed to analyze the protein expression of catalase and SOD-2, as well as Gp91phox and AT1 receptor (AT1R). MI-trained rats had significantly increased in +dP/dt and decreased left ventricular end-diastolic pressure compared with MI-sedentary rats. Moreover, oxidative stress and collagen deposition was reduced, as was myocyte hypertrophy. These effects occurred in parallel with a reduction in both AT1R and Gp91phox expression and an increase in catalase expression. SOD-2 expression was not altered. These results indicate that ET improves the functional cardiac parameters associated with attenuation of cardiac remodeling in ovariectomized rats subjected to MI. The mechanism seems to be related to a reduction in the expression of both the AT1 receptor and Gp91phox as well as an increase in the antioxidant enzyme catalase, which contributes to a reduction in oxidative stress. Therefore, ET may be an important therapeutic target for the prevention of heart failure in postmenopausal women affected by MI.     

Expression of the Integrin-Linked Kinase in a Rat Kidney Model of Chronic Allograft Nephropathy

The purpose of this study was to investigate the expression and significance of integrin-linked kinase (ILK) in the pathogenesis of chronic allograft nephropathy (CAN) in rats. For this, kidneys of Fisher (F344) rats were orthotopically transplanted into Lewis (LEW) rats. The animals were evaluated at 4, 8, 12, 16, and 24 weeks post-transplantation for renal function and histopathology. ILK protein expression was determined by Western-blot and immunohistological assays, and mRNA by RT-PCR. Our data show that 24-h urinary protein excretion in CAN rats increased significantly at week 16 as compared with F344/LEW controls. Allografts showed markedly increased mononuclear cells infiltration and presented with severe interstitial fibrosis and tubular atrophy at 16 and 24 weeks. ILK expression (protein/mRNA) was upregulated in rat kidneys with CAN, and the increase became more significant over time after transplantation. ILK expression correlated significantly with 24-h urinary protein excretion, serum creatinine levels, tubulointerstitial mononuclear cells infiltration, smooth muscle cells (SMCs) migration in vascular wall, and interstitial fibrosis. Therefore, it was concluded that ILK overexpression was the key event that involved mononuclear cells infiltration and vascular SMCs migration at early stage, and interstitial fibrosis and allograft nephroangiosclerosis at later stage of CAN pathogenesis in rats.     

Decoy receptor 3 inhibits renal mononuclear leukocyte infiltration and apoptosis and prevents progression of IgA nephropathy in mice

The progression of IgA nephropathy (IgAN), the most frequent type of primary glomerulonephritis, is associated with high levels of mononuclear leukocyte infiltration into the kidney. These cells consist mainly of T cells and macrophages. Our previous study showed that a decoy receptor 3 (DCR3) gene therapy can prevent the development of a mouse autoimmune glomerulonephritis model by its potent immune modulating effects (Ka SM, Sytwu HK, Chang DM, Hsieh SL, Tsai PY, Chen A. J Am Soc Nephrol 18: 2473-2485, 2007). Here, we tested the hypothesis that DCR3 might prevent the progression of IgAN, an immune complex-mediated primary glomerulonephritis, by inhibiting T cell activation, renal T cell/macrophage infiltration, and protecting the kidney from apoptosis. We used a progressive IgAN (Prg-IgAN) model in B cell-deficient mice, because the mice are characterized by a dramatic proliferation of activated T cells systemically and progressive NF-κB activation in the kidney. We treated the animals with short-term gene therapy with DCR3 plasmids by hydrodynamics-based gene delivery. When the mice were euthanized on day 21, we found that, compared with empty vector-treated (disease control) Prg-IgAN mice, DCR3 gene therapy resulted in 1) systemic inhibition of T cell activation and proliferation; 2) lower serum levels of proinflammatory cytokines; 3) improved proteinuria, renal function, and renal pathology (inhibiting the development of marked glomerular proliferation, crescent formation, glomerulosclerosis, and interstitial inflammation); 5) suppression of T cell and macrophage infiltration into the periglomerular interstitium of the kidney; and 5) a reduction in apoptotic figures in the kidney. On the basis of these findings, DCR3 might be useful therapeutically in preventing the progression of IgAN.     

Changes in angiotensin receptors expression play a pivotal role in the renal damage observed in spontaneously hypertensive rats

The renal renin-angiotensin system plays a central role in the development of hypertension. The aim of this work was to verify the expression of angiotensin II receptors AT(1)R and AT(2)R in the microsomal fraction of renal cortex and correlate this with the development of hypertension and renal damage in spontaneously hypertensive rats (SHR) using Wistar-Kyoto rats (WKY) as controls. AT(1)R expression increased (126%) and AT(2)R expression decreased (66%) in 4-wk-old SHR; AT(2) expression decreased in 14-wk-old SHR (61%) compared with respective age-matched WKY. These modifications were correlated to the increase in protein kinase C activity and decrease in protein kinase A activity. Four-week-old SHR showed large accumulations of macrophages in kidney glomerulus and the tubulointerstitial area, dense cortical collagen deposition, and arterial proliferative changes in the walls of arterioles and medium-sized vessels. Similar modifications were also observed in 14-wk-old SHR. Four-week-old SHR treated with losartan (30 mg·kg(-1)·day(-1)) or hydralazine (15 and 30 mg·kg(-1)·day(-1)) by gavage for 10 wk did not develop hypertension. The decrease in AT(2)R expression and renal damage observed in SHR remained even after treatment with hydralazine. On the other hand, losartan treatment prevented the modifications observed in 14-wk-old SHR, indicating that renal injuries are caused specifically by AT(1) rather than an increase in blood pressure. Our results indicate that the imbalance in AT(1)R and AT(2)R expression is associated with an inflammatory process that contributes to renal injury in adult SHR and to the development of hypertension.     

Preservation of coronary reserve by ivabradine-induced reduction in heart rate in infarcted rats is associated with decrease in perivascular collagen

We tested the hypothesis that chronically reducing the heart rate in infarcted middle-aged rats using ivabradine (IVA) would induce arteriolar growth and attenuate perivascular collagen and, thereby, improve maximal perfusion and coronary reserve in the surviving myocardium. Myocardial infarction (MI) was induced in 12-mo-old male Sprague-Dawley rats, which were then treated with either IVA (10.5 mg.kg(-1).day(-1); MI + IVA) or placebo (MI) via intraperitoneal osmotic pumps for 4 wk. Four weeks of IVA treatment limited the increase in left ventricular end-diastolic pressure and the decrease in ejection fraction but did not affect the size of the infarct, the magnitude of myocyte hypertrophy, or the degree of arteriolar and capillary growth. However, treatment reduced interstitial and periarteriolar collagen in the surviving myocardium of MI + IVA rats. The reduced periarteriolar collagen content was associated with improvement in maximal myocardial perfusion and coronary reserve. Although the rates of proliferation of periarteriolar fibroblasts were similar in the MI and MI + IVA groups, the expression levels of the AT(1) receptor and transforming growth factor (TGF)-beta(1) in the myocardium, as well as the plasma level of the ANG II peptide, were lower in treated rats 14 days after MI. Therefore, our data reveal that improved maximal myocardial perfusion and coronary reserve in MI + IVA rats are most likely the result of reduced periarteriolar collagen rather than enhanced arteriolar growth.