Renal Mass Reduction Research Articles

Tight blood pressure control decreases apoptosis during renal damage

An excess rate of apoptosis could lead to the gradual loss of renal mass. In this study, we investigated the role of apoptosis in the renal damage secondary to hypertension. Spontaneously hypertensive rats with 5/6 renal mass reduction (subtotal nephrectomy) were distributed to receive no-treatment, 200 mg/L quinapril, 360 mg/L losartan, or triple therapy (200 mg/L hydralazine, 4 mg/L reserpine, and 100 mg/L hydrochlorothiazide) for 5 weeks. Sham-operated spontaneously hypertensive rats served as controls. Age-matched Wistar-Kyoto (WKY) rats, with or without subtotal nephrectomy, were also studied. Nontreated spontaneously hypertensive rats + subtotal nephrectomy developed proteinuria, glomerular sclerosis, and tubulointerstitial lesions. In comparison to spontaneously hypertensive rats, an increment in the number of [proliferating cell nuclear antigen (PCNA)]-positive and apoptotic [terminal deoxynucleotidyl transferase (Tdt)-mediated deoxyuridine triphosphate biotin nick end labeling (TUNEL)]-positive tubular and glomerular cells was observed. By contrast, WKY + subtotal nephrectomy rats showed less severe morphologic lesions, and only the number of proliferating cells increased. By Western blot, an up-regulation of renal Bax (apoptosis inducer) was noted both in spontaneously hypertensive rats + subtotal nephrectomy and WKY + subtotal nephrectomy rats. By contrast, Bcl-xL (apoptosis protector) was up-regulated in WKY + subtotal nephrectomy rats but not in spontaneously hypertensive rats + subtotal nephrectomy. The administration of appropriate doses of quinapril, losartan, or triple therapy to spontaneously hypertensive rats + subtotal nephrectomy normalized systolic blood pressure, partially prevented proteinuria, renal lesions and apoptosis, and decreased Bax, but no changes were noted in Bcl-xL. The Bax/Bcl-xL index was significantly increased in spontaneously hypertensive rats + subtotal nephrectomy compared to sham-operated spontaneously hypertensive rats and decreased in treated groups. The combination of renal mass reduction and hypertension caused severe renal lesions associated to an increment of apoptosis rate, mainly in tubular epithelial cells. Tight blood pressure control decreased the apoptosis rate and morphologic lesions. These studies suggest that changes in the expression of apoptosis-regulatory genes contribute to the progressive damage in hypertensive rats with renal mass reduction.

The Impact of Gender on Progression of Renal Disease: Potential Role of Estrogen-Mediated Vascular Endothelial Growth Factor Regulation and Vascular Protection

Male gender is associated with a more rapid progression of renal disease independent of blood pressure, dietary protein intake, or serum lipid levels. Recently, we reported a key role for the intrarenal vasculature in progressive renal disease (Kang D-H, Kanellis J, Hugo C, Truong L, Anderson S, Kerjaschki D, Schreiner GF, Johnson RJ: Role of endothelium in progressive renal disease. J Am Soc Nephrol 2002, 13:806-816). We hypothesized that estrogen-mediated preservation of the renal vasculature could account for the better renal outcome in female rats. We analyzed micro- and macrovascular changes in the 5/6 remnant kidney (RK) models both in male (n = 24) and female (n = 24) Sprague-Dawley rats up to 12 weeks after renal mass reduction. At 12 weeks, male and female RK rats had equivalent blood pressure, glomerular tuft area, and RK/body weight, but male rats showed worse renal function, proteinuria, glomerulosclerosis (%), and tubulointerstitial fibrosis. At 12 weeks peritubular capillary (PTC) EC proliferation and PTC density were higher in female RK rats whereas macrovascular changes in preglomerular vessels (smooth muscle cell proliferation, medial wall thickening, and adventitial fibrosis) were less prominent. The expression of vascular endothelial growth factor (VEGF) and VEGF type 2 receptor (flk-1) in renal cortex assessed by immunostaining were higher in female RK rats. To dissect the mechanism of sex hormone-induced vascular remodeling and VEGF regulation, we investigated the in vitro effect of 17 beta-estradiol (17 beta E, 10 nmol/L) on proliferation and VEGF expression of renal tubular cells (rat proximal tubular cells), vascular smooth muscle cells (VSMCs), and human umbilical vein endothelial cells (HUVECs). 17 beta E directly stimulated the proliferation of HUVECs, whereas it inhibited serum-induced proliferation of VSMCs. 17 beta E stimulated VEGF mRNA expression both in renal tubular cells and VSMCs. However, when cells were pretreated with a nitric oxide donor to simulate the in vivo condition, 17 beta E inhibited VEGF mRNA expression and protein release in VSMCs. In conclusion, female RK rats developed less glomerulosclerosis and renal failure compared to male RK rats in association with greater preservation of PTC and less preglomerular arteriopathy. Estrogen stimulated basal VEGF expression in renal tubular cells. We propose that estrogen may protect female rats in progressive renal disease by stimulating VEGF expression and maintaining a healthy intrarenal vasculature.

Blood pressure lability and glomerulosclerosis after normotensive 5/6 renal mass reduction in the rat

Hypertension plays a major role in the progression of both experimental and clinical chronic renal disease. However, the pathogenesis of the more slowly developing glomerulosclerosis that is seen even in the absence of overt hypertension, both in renal mass reduction models and in humans with chronic renal disease, remains controversial. The relationship of such glomerulosclerosis to the ambient blood pressure profiles was examined in the normotensive approximately 5/6 surgical excision rat remnant kidney model. Blood pressure was radiotelemetrically monitored at 10-minute intervals for 15 to 16 weeks ( approximately 15,000 blood pressure readings) in untreated rats (N= 13), or those treated with enalapril (N= 8), amlodipine (N= 9), or a combination of hydralazine, reserpine, and hydrochlorothiazide (N= 10). Even in these normotensive rats (systolic blood pressure <140 mm Hg), % glomerulosclerosis was significantly correlated with the overall average systolic blood pressure (r= 0.62, P < 0.0001; N= 40). However, much stronger correlations were observed between glomerulosclerosis and the % systolic blood pressure readings >150 mm Hg (r= 0.77, P < 0.0001) and the standard deviation of the average systolic blood pressure (r= 0.87, P < 0.0001). These data indicate that pressure dependent injury mechanisms continue to contribute to glomerular injury even within the "normotensive" blood pressure range in rats with reduced renal mass. This most likely represents the consequence of the impairment of protective renal autoregulation and enhanced glomerular transmission of the blood pressure fluctuations into the hypertensive range characteristic of the conscious state in both experimental animals and in humans. Such pathophysiology supports the need for more aggressive and around-the-clock blood pressure control in chronic renal disease.

Initial angiogenic response in reduced renal mass after transplantation

Introduction.Shortage of organs is a major problem in kidney transplantation and requires novel strategies to increase the number of kidney transplants. To reduce the shortage of kidneys, we have proposed transplantation of two halves of one kidney into two recipients (hemirenal transplantation, HRT) and have shown its feasibility in pig and human kidneys. However, reduced renal mass can lead to progressive renal failure in rodents and can reduce the longevity of kidney transplants in humans. Recent studies suggest that derangement of angiogenesis plays a role in the progressive renal failure after reduction in renal mass in rodents. However, since the renal physiology of rats is different from that of large animals, we studied angiogenesis in reduced renal mass transplants in pigs and determined if the reduction in renal mass has the same effect in large animals as that in rodents. Materials and methods.Kidney autotransplantation was performed in domestic outbred swine. Heminephrectomy of the autotransplanted kidney and nephrectomy of the contralateral kidney were performed 1 week after transplantation to reduce the renal mass. Four weeks after transplantation, the pigs were sacrificed and the hemirenal and control nephrectomy specimens were processed for morphometric analysis of glomerular capillary density and immunohistochemical analysis of VEGF expression. Soluble extracts from the kidneys were tested in an in vitro angiogenesis assay to determine their activity to influence angiogenesis. Statistical analysis with ANOVA was performed on the glomerular capillary density in kidney specimens. Results.All these parameters of angiogenesis were increased in the reduced renal mass autotransplants as compared to normal kidneys or whole kidney autotransplants. Glomerular capillary density was increased significantly after reduction in renal mass. VEGF expression also was increased progressively by the third week after reduction in renal mass. Soluble extract from the reduced renal mass transplants significantly increased the in vitro angiogenesis. Conclusion.This is the first study to demonstrate that angiogenesis is increased in the initial stages of reduction in renal mass after transplantation in a large animal model. Increased angiogenesis was found in this model earlier than reported in small animal models (2 weeks in pigs versus 6 weeks in rats). Taken together with other studies, our data suggest that derangement in angiogenesis could play an important role in long-term graft function after hemirenal transplantation.

Renal and Vascular Nitric Oxide System in Reduced Renal Mass Saline Hypertension

Background: Reduction in renal mass is associated with several structural and functional adaptations including compensatory renal growth and hemodynamic changes. The mediators of the renal hemodynamic adaptations have not been definitively identified. Several investigators have postulated that nitric oxide (NO) is involved this physiological mechanisms. The purpose of this study was to evaluate the role of vascular and renal NO pathway in the model of subtotal nephrectomy-salt load hypertension. Materials and Methods: Wistar rats with 75% renal mass reduction (RMR) and saline load were studied during 4 weeks. Weekly, indirect systolic blood pressure (SBP) were measured. One week after nephrectomy, animals were divided in two groups, hypertensive (SBP > 140 mm Hg) and normotensive (SBP < 140 mm Hg). Urinary excretion of nitrates and nitrites (NOx), urinary chemioluminiscence levels and NOS activity in the left kidney and in the thoracic aorta artery were determined at the fourth week after subtotal nephrectomy. Results: Urinary excretion of sodium was higher in normotensive rats than hypertensive rats and in both groups this parameter was higher than in sham rats. NOx excretion and NOS activity in the different nephron segments were higher in normotensive rats than in the hypertensive ones. In contrast, NOS activity in aorta sections and urinary chemiluminescence levels in hypertensive animals were enhanced compared with normotensive rats. These parameters were higher in both groups of nephrectomized rats than in sham ones. Conclusion: This study provides evidence to support the fact that the activation of the renal NO system is an important mechanism whereby the remnant kidney regulates sodium and water balance, contributing to control the arterial blood pressure in the renal mass reduction and saline load model.

Protection of wistar furth rats from chronic renal disease is associated with maintained renal nitric oxide synthase.

Wistar Furth (WF) rats do not develop renal injury after severe reduction of renal mass. Because clinical and animal studies suggested that nitric oxide (NO) deficiency occurs and may contribute to chronic renal disease (CRD), the status of the NO system in WF versus Sprague Dawley (SD) rats was examined with the 5/6 renal ablation/infarction (A/I) model of CRD. Eleven weeks after A/I, SD rats developed proteinuria, severe kidney damage, decreased renal function, and marked decreases in total and renal NO synthase (NOS), specifically neuronal NOS. In contrast, WF rats exhibited elevated baseline and maintained post-A/I total NO production, with no decrease in renal cortex NOS activity despite a decrease in remnant neuronal NOS abundance. When low-dose chronic Nomega-nitro-L-arginine methyl ester treatment was added for WF A/I-treated rats, rapid progression of CRD was observed. In conclusion, elevated NO production in WF rats was associated with protection from the progression of CRD after renal mass reduction. The protection might be attributable to greater total and renal NO-generating capacity and increased nephron number, compared with SD rats. NOS inhibition rendered WF rats susceptible to progression, suggesting a possible critical threshold for NO production, below which renal injury occurs.

Mast cell infiltration and chemokine expression in progressive renal disease

Mast cells are growth factor-rich, bone marrow-derived cells that infiltrate injured tissue where they have been implicated in the pathogenesis of progressive fibrosis. Mast cell infiltration and the expression of related chemoattractants was examined following 5/6 nephrectomy, a model of progressive, nonimmune-mediated renal injury. In addition, expression of the profibrotic cytokine, transforming growth factor-beta (TGF-beta) within mast cells and the effects of renoprotective therapy with angiotensin-converting enzyme (ACE) inhibition were also determined. Renal injury was accompanied by mast cell infiltration, in close proximity to areas of tubulointerstitial fibrosis. Mast cells displayed toluidine blue metachromasia and were immunopositive for TGF-beta1 as well as chymase and tryptase. The expression of several mast cell chemokines, including stem cell factor, interleukin-8 (IL-8), and also TGF-beta1, were increased in 5/6 nephrectomized kidneys. ACE inhibition with ramipril led to a reduction in renal injury in association with attenuation of mast cell infiltration and chemokine expression. Mast cell infiltration and related chemokine expression are prominent and early features following renal mass reduction and may contribute pathogenetically to progressive renal injury.

Glomerular and renal vascular structural changes in alpha8 integrin-deficient mice.

Integrins are matrix receptors that regulate cell-matrix interactions during development and in adult tissue. In the adult kidney, the alpha8 chain is specifically expressed in glomerular mesangial cells and vascular smooth muscle cells. alpha8-deficient (alpha8-/-) mice demonstrate reductions in renal mass, which can range from complete renal agenesis to the development of kidneys that are only slightly smaller than wild-type kidneys. No histologic abnormalities of these kidneys have been described. However, considering the prominent expression of alpha8 in glomeruli and renal vessels, it seemed unlikely that the kidneys of alpha8-/- mice would be completely normal. Therefore, the renal phenotype of adult alpha8-/- mice was investigated, for assessment of more subtle morphologic alterations in kidney tissue. alpha8-/- mice displayed a significant reduction in nephron number and an increase in glomerular volume, compared with wild-type control animals. Albuminuria was not different in wild-type and alpha8-/- mice. Quantitative morphologic analyses revealed that the glomeruli of alpha8-/- mice were hypercellular, with an increased number of mesangial cells, compared with wild-type mice. Mesangial matrix deposition (as demonstrated for collagen IV and the alpha8 ligand fibronectin) was expanded in alpha8-/- mice, compared with wild-type mice. Collagens I and III, which are not normally present in glomeruli, were detected in the glomeruli of alpha8-/- mice. Staining for other glomerular integrins demonstrated an increased abundance of the collagen receptor alpha2 integrin in alpha8-/- mice. The glomerular capillary length density was significantly greater in alpha8-/- mice than in wild-type mice. Cortical arterial vessel walls were not altered in alpha8-/- mice, but the capillaries of the peritubular network were widened. Despite the strong mesangial and vascular expression of alpha8, glomerular and renal vascular alterations in alpha8-/- mice were relatively mild. Only aged alpha8-/- mice demonstrated increased glomerular capillary widening, compared with control animals. The results suggest that the lack of alpha8 can be largely compensated for, at least in younger alpha8-/- mice. It is not yet clear whether the occurrence of collagens that are not normally present in glomeruli and the increased abundance of the collagen receptor alpha2 contribute to maintaining the glomerular structure in alpha8-/- mice. The compensatory mechanisms involved will be the subject of future research.

Correlation Between Glomerular Size and Long-Term Renal Function in Patients with Substantial Loss of Renal Mass

Focal segmental glomerulosclerosis and progressive renal failure have been reported in reduced renal mass models. However, these findings are not consistent across all species. Increased intracapillary pressure and chronic glomerular hyperfiltration have been shown to contribute to this progression. Studies also have shown that a strong correlation exists between higher glomerular size and the degree of glomerular sclerosis that develops following loss of functioning nephrons. To evaluate the relationship between glomerular size and long-term renal function following massive renal mass removal we describe 9 patients with less than 50% renal mass. All patients had undergone initial nephrectomy followed by partial second nephrectomy, with 30% to 50% of the second kidney excised for localized tumor. In 3 patients moderate to severe renal failure developed. Mean planar glomerular area (MPA) was 29.45 +/- 2.2 mm3 for all patients. Multivariate linear regression analysis demonstrated a significant association between MPA 30 mm3 or greater and increased serum creatinine. For patients with MPA 30 mm3 or greater the predicted delta creatinine was 2.43 mg/dl higher than that in patients with MPA less than 30 mm3 (p = 0.0028). Age was the only other covariate significantly associated with outcome in multivariate analysis. Our data indicate an individual susceptibility toward developing renal failure after significant renal mass reduction. We suggest that patients with less than 50% renal mass and higher MPA are at greater risk for progressive renal failure. MPA may be used as a marker in high risk patients with substantial loss of renal mass to predict long-term renal function.

Tubular shear stress and phenotype of renal proximal tubular cells.

Phenotypic alterations resulting from flow-induced mechanical strains is a growing field of research in many cell types such as vascular endothelial and smooth muscle cells, chondrocytes, and osteocytes. Because renal mass reduction is followed by a dramatic increase in GFR in the remaining nephron, modulation of tubular cell phenotype by flow-induced mechanical strains could be one of the events initiating the deleterious pathways that lead to the destruction of renal parenchyma after renal mass reduction. This study demonstrates that increased flow induced, in vitro and in vivo, a reinforcement of the apical domain of actin cytoskeleton and an inhibition of plasminogen activator expression. These effects of flow on plasminogen activator expression were prevented by blocking the reorganization of actin cytoskeleton and were associated with an increase in a shear-stress responsive element binding activity. These results confirm that tubular flow affects the phenotype of renal epithelial cells and suggest that flow-induced mechanical strains could be one determinant of tubulointerstitial lesions during the progression of renal diseases.

Proteinuria and phenotypic change of proximal tubular cells.

Terminal renal failure is the final common fate of chronic nephropathies independent of the type of initial insult. The outstanding review by Brenner et al. (1) in 1982 introduced the idea that glomerular hemodynamic changes that develop as compensatory adaptation to irreversible nephron damage cause progressive deterioration of function and structure of the remaining nephrons. After reduction of renal mass in rats, remnant intact nephrons undergo sudden hypertrophy with concomitant lowering of arteriolar resistance and increased glomerular plasma flow that results from a differential decrease in vessel tone that is less in afferent than efferent arterioles. This fosters adaptive increase in glomerular capillary hydraulic pressure and more filtrate per nephron, changes, however, that are detrimental in the long term. The increase in intraglomerular capillary pressure alters the size-selective function of the glomerular barrier and causes protein ultrafiltration. Abnormally filtered proteins have an intrinsic renal toxicity linked to their over-reabsorption by proximal tubular cells and activation of tubular-dependent pathways of interstitial inflammation and fibrosis (2,3). The functional importance of tubulointerstitial events in progressive renal disease is supported by evidence that the severity of tubular interstitial damage strongly correlates with the risk of renal failure, even better than do the glomerular lesions. The relationship between proteinuria and tubulointerstitial damage was suggested by early studies in renal biopsies of rats with age-related proteinuria (4) and adriamycin nephrosis (5), showing that protein reabsorption droplets accumulate in the cytoplasm of proximal tubular cells with focal breaks of the tubular basement membrane and extravasation of the tubular content into the renal interstitium, followed by an inflammatory reaction and tubulointerstitial lesions. Furthermore, in models of overload proteinuria, repeated injections of albumin in the rat increased glomerular barrier permeability and caused massive proteinuria (6,7) and tubular changes with heavy macrophage and T-lymphocyte infiltration into the renal interstitium (8). That excess protein reabsorption by proximal tubular cells may play a role in the development of interstitial inflammation has been documented by a recent study of our group in two different models of proteinuric nephropathies (9). In rats with 5/6 nephrectomy, albumin and IgG accumulation in proximal tubular cells was visualized in the early stage, preceding the interstitial infiltration of major histocompatability complex II–positive cells and macrophages. The infiltrating cells concentrated almost exclusively in regions containing IgG-positive proximal tubules and tubules with luminal casts. Similar patterns were found in the immune model of passive Heymann nephritis indicating that the interstitial inflammatory reaction develops at the sites of protein overload, regardless of the type of glomerular injury. Protein Traffic as a Fosterer of Tubular Cell Dysfunction Filtered albumin and other proteins that accumulate within intracellular compartments of proximal tubular cells perturb cell function by several mechanisms. Studies have contributed to define the biochemical pathways specifically activated by excessive tubular reabsorption, and evidence is now available that protein overloading of proximal tubular cells in culture activates the transcription of a number of genes encoding for vasoactive, inflammatory, and fibrogenic molecules with potential toxic effects on the kidney.

Role of oxidative stress in angiotensin-induced hypertension.

Infusion of ANG II at a rate not sufficient to evoke an immediate vasoconstrictor response, produces a slow increase in blood pressure. Circulating levels of ANG II may be within ranges found in normotensive individuals, although inappropriately high with respect to sodium intake. When ANG II levels are dissociated from sodium levels, oxidative stress (OXST) occurs, which can increase blood pressure by several mechanisms. These include inadequate production or reduction of bioavailability of nitric oxide, alterations in metabolism of arachidonic acid, resulting in an increase in vasoconstrictors and decrease in vasodilators, and upregulation of endothelin. This cascade of events appears to be linked, because ANG II hypertension can be blocked by inhibition of any factor located distally, blockade of ANG II, OXST, or endothelin. Such characteristics are shared by other models of hypertension, such as essential hypertension, hypertension induced by reduction in renal mass, and renovascular hypertension. Thus these findings are clinically important because they reveal 1) uncoupling between ANG II and sodium, which can trigger pathological conditions; 2) the various OXST mechanisms that may be involved in hypertension; and 3) therapeutic interventions for hypertension developed with the knowledge of the cascade involving OXST.

"Step" vs. "dynamic" autoregulation: implications for susceptibility to hypertensive injury.

Renal autoregulatory (AR) mechanisms provide the primary protection against transmission of systemic pressures, and their impairment is believed to be responsible for the enhanced susceptibility to hypertensive renal damage in renal mass reduction (RMR) models. Assessment of AR capacity by the "step" change methodology under anesthesia was compared with that by "dynamic" methods in separate conscious control Sprague-Dawley rats and after uninephrectomy (UNX) and (3/4) RMR (RK-NX) (n = 7-10/group). Substantially less AR capacity was seen by the dynamic vs. the step methodology in control rats. Moreover, dynamic AR capacity did not differ among controls, UNX, and RK-NX rats (fractional gain in admittance approximately 0.4-0.5 in all groups at frequencies in the range of 0.0025-0.025 Hz). By contrast, significant impairment of step AR was seen in RK-NX vs. control or UNX rats (AR indexes 0.7 +/- 0.1 vs. 0.1 +/- 0.02 and 0.2 +/- 0.04, respectively, P < 0.01). We propose that the step and dynamic methods evaluate the renal AR responses to different components of blood pressure (BP) power with the step AR assessing the ability to buffer large changes in average BP (DC power), whereas the present "dynamic" methods assess the AR ability to buffer slow BP fluctuations (<0.25 Hz) superimposed on the average BP (AC power), a substantially smaller component of total BP power. We further suggest that step but not dynamic AR methods as presently performed provide a valid index of the underlying susceptibility to hypertensive glomerular damage after RMR.

Long-term protein intake control in kidney transplant recipients: Effect in kidney graft function and in nutritional status

Background: Reduction in renal mass is followed by progressive renal failure. The reduction in filtration surface area, caused by the absence of 50% of renal mass, in patients with customary salt intake is followed by expansion of extracellulary volume and systemic and glomerular hypertension. High protein intake may contribute to renal allograft injury arising from insufficient renal mass. Methods: The authors studied outcome of 48 patients with kidney transplant to whom normocaloric diets and moderate intake of protein (0.8 g/kg), of sodium (3 g/d), and lipids (no more than 30% of total energy) were prescribed. Monthly 24-hour urea excretion and 24-hour sodium excretion were measured. Renal function was assessed by creatinine clearances and by renal scintigraphy. The 30 patients who followed prescriptions exactly were the compliant group (group 1). The other 18, who followed the diet prescribed only partially (their intakes were 1.4 g/kg of protein and 5 g/d of sodium) were the control group (group 2). Results: Patients of the compliant group maintained unchanged renal function, whereas patients of the control group lost more than 40% of excretion efficiency as a mean. Conclusions: Dietary restrictions of protein and sodium can stabilize renal function in patients with kidney transplant. Wider use of this treatment is indicated. Am J Kidney Dis 41(S1):S146-S152. © 2003 by the National Kidney Foundation, Inc.

Hyperfiltration and glomerulosclerosis.

Nearly 70 years ago, the association between reduction in renal mass and subsequent glomerular injury was established. Later the pathologic changes were attributed to adaptive hemodynamic changes in the residual nephrons. This relationship seems to exist in a number of experimental animal species, as well as humans. Among the various hemodynamic changes that occur within residual nephrons, the increase in glomerular pressure is the most important in generating subsequent pathologic changes. The renin-angiotensin-aldosterone system seems to contribute to the intrarenal pressure. Both angiotensin and aldosterone participate. Increases in glomerular pressure appear to act on the mesangial compartment causing it to increase its cell number and matrix volume. Deleterious interactions between higher pressures, increased capillary volume, and a relatively fixed podocyte number also appear to contribute to the sclerotic process. Endothelial cell changes occur perhaps in response to direct hemodynamic stimuli, but their role in the sclerotic process is less clear than those of mesangial and glomerular epithelial cells.

Hyperfiltration and glomerulosclerosis

Nearly 70 years ago, the association between reduction in renal mass and subsequent glomerular injury was established. Later the pathologic changes were attributed to adaptive hemodynamic changes in the residual nephrons. This relationship seems to exist in a number of experimental animal species, as well as humans. Among the various hemodynamic changes that occur within residual nephrons, the increase in glomerular pressure is the most important in generating subsequent pathologic changes. The renin-angiotensin-aldosterone system seems to contribute to the intrarenal pressure. Both angiotensin and aldosterone participate. Increases in glomerular pressure appear to act on the mesangial compartment causing it to increase its cell number and matrix volume. Deleterious interactions between higher pressures, increased capillary volume, and a relatively fixed podocyte number also appear to contribute to the sclerotic process. Endothelial cell changes occur perhaps in response to direct hemodynamic stimuli, but their role in the sclerotic process is less clear than those of mesangial and glomerular epithelial cells. © 2003 Elsevier Inc. All rights reserved.

Progression of renal failure with anaemia and multiple effects of angiotensin-converting enzyme inhibitor in rats with renal mass reduction

Several factors such as proteinuria and renal fibrosis may be important in the progression of many forms of chronic renal diseases. The purposes of the current study were to investigate the progressive renal failure of the rats with surgical renal mass reduction (RMR) and the effect of the angiotensin-converting enzyme (ACE) inhibitor, lisinopril, and to document correlation of several factors associated with progressive renal failure. Rats were subtotal (5/6) nephrectomized by resection of the renal poles and sham-operated. The functional, histological and haematological changes of the rats were studied for up to 10 weeks. After 2 weeks of RMR, oral administration of lisinopril (10 mg kg −1 per day) was performed for 8 weeks. RMR resulted in progressive renal failure with proteinuria, monocyte/macrophage (ED1 +) infiltration, anaemia as assessed by haemoglobin and haematocrit (Htc), renal hypertrophy as assessed by left kidney to body weight ratio (BKW/BW), and renal fibrosis as assessed by glomerular lesions and tubulointerstitial changes. Lisinopril exhibited renoprotection with antiproteinuric effect and inhibition of monocyte/macrophage (ED1 +) infiltration. However, beneficial effect of lisinopril on anaemia was not observed. At 10 weeks after surgery, severity of proteinuria positively correlated with plasma creatinine (Pcr), BKW/BW, histological damage, and systolic blood pressure, and negatively correlated with haemoglobin. Severity of tubulointerstitial changes positively correlated with Pcr and blood urea nitrogen, and negatively correlated with haemoglobin and Htc. Moreover, monocyte/macrophage (ED1 +) infiltration positively correlated with severity of proteinuria and tubulointerstitial changes. These findings strongly support that proteinuria, monocyte/macrophage infiltration and renal fibrosis appear to play principal roles in the progressive renal failure with anaemia and renoprotection of ACE inhibition may be mediated by multiple actions of ACE inhibitor. The present study confirms that rats with RMR is useful to explore target molecules for renoprotective drugs and evaluate renoprotective effect of new molecular entities.

End-stage renal disease and acute glomerulonephritis in Goajiro Indians

Goajiro Indians are a semi-nomad tribe that live on the Goajiro peninsula, in the northwestern part of Venezuela. We investigated the incidence of end-stage renal disease (ESRD) and post-streptococcal glomerulonephritis (PSGN) among Goajiros and to determine if it was increased and whether congenital endowment of low number of nephrons (as indicated by low birth weight) was a contributing factor in their predisposition to chronic renal failure (CRF). The incidence of ESRD and the attack rate of poststreptococcal glomerulonephritis (PSGN) among Goajiros during the period December 1991 through December 1998 were evaluated from the records of the University Hospital, in Maracaibo, which is the referral center for Goajiro Indians. Demographic characteristics and birth weight were obtained from the records of the Regional Public Health Service. Subclinical reduction in renal functioning mass was investigated in 11 healthy Goajiros with a standardized tubular stress test that determines the increment in tubular secretion of creatinine (TSCr) resulting from the intravenous administration of a bolus of creatinine. The incidence of ESRD among Goajiros was 220 patients per million inhabitants per year, 1.7 times higher than the incidence for the country. The attack rate of post-streptococcal glomerulonephritis is nearly double among Goajiro Indians (2.9 +/- 1.3 cases/100,000 inhabitants/year) than in the general population in the neighboring Maracaibo city (1.5 +/- 0.3, P < 0.02). Low weight birth was common among Goajiros; as many as 23% of newborns weigh less than 1000 g. The stimulated TSCr in healthy Goajiros was 30% lower than in controls (P < 0.001). Goajiro Indians have a high incidence of ESRD. A high attack rate of PSGN and low nephron endowment in combination may be responsible, at least in part, for the increased risk of ESRD in this population.

Early endothelial dysfunction following renal mass reduction in rats.

Endothelial dysfunction has been previously described in severely hypertensive rats with renal mass reduction (RMR) receiving large dietary Na loads. Because hypertension and Na loading reduce endothelium-dependent vasodilation, the effect of renal failure per se is unclear. Responses to acetylcholine in noradrenaline-contracted isolated perfused mesenteric arteries were studied. Vessels were obtained from RMR rats kept on a normal diet, 3 and 10 days after surgery, and the results were compared with those from sham-operated rats (SN). The role of three putative mediators of endothelium-dependent vasodilation was assessed using: L-NAME (10(-4) mol L(-1)); indomethacin (INDO, 10(-5) mol L(-1)); and a mixture of charybdotoxin and apamin (C/A, both 10(-7) mol L(-1)), inhibitors of Ca-activated K-channels to mediate the effects of endothelium-derived hyperpolarizing factor (EDHF). Response to acetylcholine but not that to nitroprusside (endothelium-independent) was decreased in RMR. L-NAME reduced further acetylcholine relaxations in SN but not in RMR. By contrary, INDO decreased acetylcholine vasodilation in RMR but had no effect in SN. C/A had similar effects in the SN and RMR rats. The levels of 6-keto prostaglandin F1alpha were elevated in the urine of the RMR rats and were perfusate from the RMR vessels. Endothelial dysfunction occurs early after RMR, even when systolic blood pressure is only minimally elevated and Na intake is normal. This alteration may be because of decreased availability of nitric oxide, partially compensated by increased prostacyclin production.

Increased Dietary Potassium and Magnesium Attenuate Experimental Volume Dependent Hypertension Possibly Through Endogenous Sodium‐Potassium Pump Inhibitor

We and others have shown that inhibition of cardiovascular muscle (CVM) cell Na+,K‐ATPase activity (NKPTA) due to increased level of endogenous sodium potassium pump inhibitor (SPI) is involved in the mechanism of volume expanded (VE) experimental and human essential hypertension (HT). Since diets fortified with very high potassium (K) or very high magnesium (Mg) decrease blood pressure (BP), we have examined the effect of a moderate increase in dietary K alone and a moderate increase in dietary K and Mg on plasma levels of SPI, CVM cell NKPTA, and BP in reduced renal mass (RRM)‐salt HT rats, a classical model of VE HT. Seventy Percent‐RRM rats were divided in four dietary groups, (1) Na free and normal K and Mg (0Na–K–Mg); (2) normal Na, K and Mg (Na–K–Mg); (3) normal Na and high K (2 ×normal), and normal Mg (Na–2K–Mg); and (4) normal Na and high K (2 ×normal), and high Mg (2 ×normal) (Na–2K–2Mg). As expected, compared to control 0Na–K–Mg rats, Na–K–Mg rats developed HT. Blood pressure increased significantly less in Na–2K–Mg rats whereas, BP did not increase in Na–2K–2Mg rats. Hypertension in NA–K–Mg rats was associated with an increase in plasma SPI and digitalis like factor (DIF) and a decrease in renal and myocardial NKPTA. However, doubling the Mg along with K in the diet (Na–2K–2Mg) normalized SPI and DIF and increased myocardial and renal NKPTA, compared to control 0Na–K–Mg rats. Also, compared to 0Na–K–Mg rats, water consumption, urine excretion, urinary sodium excretion urinary potassium excretion (UNaV), and (UKV) increased in the other three groups, more so in Na–2K–2Mg rats. These data show that K and Mg have additive effects in preventing an increase in SPI, thus probably preventing the BP increase in RRM rats.