Effects of angiotensin II receptor blockade on remnant glomerular permselectivity

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

N-acetylcysteine ameliorates acute kidney injury but not glomerular hemorrhage in an animal model of warfarin-related nephropathy

Warfarin-related nephropathy (WRN) occurs under conditions of overanticoagulation with warfarin. WRN is characterized by glomerular hemorrhage with occlusive tubular red blood cell (RBC) casts and acute kidney injury (AKI). Herein we test the hypothesis that oxidative stress plays a role in the AKI of WRN. 5/6 Nephrectomy rats were treated with either warfarin (0.04 mg·kg⁻¹·day⁻¹) alone or with four different doses of the antioxidant N-acetylcysteine (NAC). Also tested was the ability of our NAC regimen to mitigate AKI in a standard ischemia-reperfusion model in the rat. Warfarin resulted in a threefold or greater increase in prothrombin time in each experimental group. Serum creatinine (Scr) increased progressively in animals receiving only warfarin + vehicle. However, in animals receiving warfarin + NAC, the increase in Scr was lessened, starting at 40 mg·kg⁻¹·day⁻¹ NAC, and completely prevented at 80 mg·kg⁻¹·day⁻¹ NAC. NAC did not decrease hematuria or obstructive RBC casts, but mitigated acute tubular injury. Oxidative stress in the kidney was increased in animals with WRN and it was decreased by NAC. The NAC regimen used in the WRN model preserved kidney function in the ischemia-reperfusion model. Treatment with deferoxamine (iron chelator) did not affect WRN. No iron was detected in tubular epithelial cells. In conclusion, this work taken together with our previous works in WRN shows that glomerular hematuria is a necessary but not sufficient explanation for the AKI in WRN. The dominant mechanism of the AKI of WRN is tubular obstruction by RBC casts with increased oxidative stress in the kidney.

Fetal uninephrectomy in male sheep alters the systemic and renal responses to angiotensin II infusion and AT1R blockade

Fetal uninephrectomy (uni-x) at 100 days of gestation results in compensatory nephrogenesis in the remaining kidney, resulting in a 30% reduction in total nephron number in male sheep. Recently, we showed that uni-x males at 6 mo of age have elevated arterial pressure, reduced renal blood flow (RBF), glomerular filtration rate (GFR), and low plasma renin levels (Singh R, Denton K, Bertram J, Jefferies A, Head G, Lombardo P, Schneider-Kolsky M, Moritz K. J Hypertens 27: 386–396, 2009; Singh R, Denton K, Jefferies A, Bertram J, Moritz K. Clin Sci (Lond) 118: 669–680, 2010). We hypothesized this was due to upregulation of the intrarenal renin-angiotensin system (RAS). In this study, renal responses to ANG II infusion and ANG II type 1 receptor (AT1R) blockade were examined in the same 6-mo-old male sheep. Uni-x animals had reduced levels of renal tissue and plasma renin and ANG II. Renal gene expression of renin, and gene and protein levels of AT1R and AT2R, were significantly lower in uni-x animals. In response to graded ANG II infusion, sham animals had the expected decrease in conscious RBF and GFR. Interestingly, the response was biphasic in uni-x sheep, with GFR initially decreasing, but then increasing at higher ANG II doses (34 ± 7%; Pgroup × treatment < 0.001), due to a paradoxical decrease in renal vascular resistance ( Pgroup × treatment < 0.001). In response to AT1R blockade, while GFR and RBF responded similarly between groups, there was a marked increase in sodium excretion in uni-x compared with sham sheep (209 ± 35 vs. 25 ± 12%; P < 0.001). In conclusion, in 6-mo-old male sheep born with a single kidney, these studies demonstrate that this is a low-renin form of hypertension, in which responses to ANG II are perturbed and the intrarenal RAS is downregulated.

Effect of ACE inhibition on glomerular permselectivity and tubular albumin concentration in the renal ablation model

Despite the central role of tubular plasma proteins that characterize progressive kidney diseases, protein concentrations along the nephron in pathological conditions have not been quantified so far. We combined experimental techniques and theoretical analysis to estimate glomerular and tubular levels of albumin in the experimental model of 5/6 nephrectomy (Nx) in the rat, with or without angiotensin-converting enzyme (ACE) inhibition. We measured glomerular permselectivity by clearance of fluorescent Ficoll and albumin and used theoretical analysis to estimate tubular albumin. As expected, 5/6 Nx induced an elevation of the fractional clearance of the largest Ficoll molecules (radii >56 Å, P < 0.05), increasing the importance of the shunt pathway of the glomerular membrane and the albumin excretion rate (119 ± 41 vs. 0.6 ± 0.2 mg/24 h, P < 0.01). ACE inhibition normalized glomerular permselectivity and urinary albumin (0.5 ± 0.3 mg/24 h). Theoretical analysis indicates that with 5/6 Nx, an increased albumin filtration overcomes proximal tubule reabsorption, with a massive increase in average albumin concentration along the tubule, reaching the highest value of >2,500 μg/ml at the end of the collecting duct. ACE inhibition improved glomerular permselectivity, limiting albumin filtration under proximal tubule reabsorption capacity, with low albumin concentration along the entire nephron, averaging <13 μg/ml at the end of the collecting duct. These results reinforce our understanding of the mechanisms of renal disease progression and the effects of angiotensin II antagonism. They also suggest that evaluation of tubular protein concentration levels could help to identify patients at risk of kidney disease progression and to improve clinical management.

Amelioration of glomerulosclerosis with all-trans retinoic acid is linked to decreased plasminogen activator inhibitor-1 and α-smooth muscle actin

AIM

To examine the effects of all-trans retinoic acid (atRA) on renal morphology and function as well as on renal plasminogen activator inhibitor-1 (PAI-1) expression and plasmin activity in rats with 5/6 nephrectomy.

METHODS

Adult male Sprague Dawley rats were given 5/6 nephrectomy or sham operation. Renal function was measured 2 weeks later. The nephrectomized rats were assigned to groups matched for proteinuria and treated with vehicle or atRA (5 or 10 mg/kg by gastric gavage once daily) for the next 12 weeks. Rats with sham operation were treated with vehicle. At the end of the treatments, kidneys were collected for histological examination, Western blot analysis, and enzymatic activity measurements.

RESULTS

The 5/6 nephrectomy promoted hypertension, renal dysfunction, and glomerulosclerosis. These changes were significantly reduced in the atRA-treated group. The expressions of PAI-1 and α-smooth muscle actin (α-SMA) were significantly increased in the vehicle-treated nephrectomized rats. Treatment with atRA significantly reduced the expressions of PAI-1 and α-SMA. However, plasmin activity remained unchanged following atRA treatment.

CONCLUSION

Treatment with atRA ameliorates glomerulosclerosis and improves renal function in rats with 5/6 nephrectomy. This is associated with a decrease in PAI-1 and α-SMA, but not with a change in plasmin activity.

Regulation of angiotensin II type I receptor (AT1R) protein levels in the obese Zucker rat kidney and urine

Increased renal expression of the angiotensin II, type-1 receptor (AT1R) has been associated with increased blood pressure (BP) and progression of renal disease. We tested whether common medications used to treat hypertension and the metabolic syndrome alter renal AT1R; and whether urine AT1R can be used as a reasonable noninvasive marker of renal levels in the obese Zucker rat, a model for human metabolic syndrome. Immunoblotting revealed that renal and urinary levels of AT1R were significantly higher in obese versus lean rats and correlated (R = 0.62, p < 0.05). Chronic treatment with BP lowering, candesartan, an AT1R antagonist, increased renal levels of AT1R in both lean (282% of lean controls) and obese (178% of obese controls) rats, but decreased urine AT1R levels in obese rats (72% of obese controls). Similarly, chronic treatment with rosiglitazone (RGZ), a peroxisome proliferator activated receptor (subtype gamma) agonist, significantly decreased urine (43% of obese controls) but not renal AT1R (105%) in obese rats. Blood pressure, measured by radiotelemetry, was significantly correlated in untreated and RGZ-treated rats to renal AT1R (R = 0.57, p = 0.0035). Finally, high- (4%) and medium- (0.4%) NaCl diets increased excretion of AT1R in obese rats to approximately 400% of low- (0.04%) NaCl diet. This effect was markedly blunted in lean rats. Overall, we demonstrate increased renal AT1R levels in obese rats. Urine AT1R correlated with renal levels only in the untreated state. Relative salt-sensitivity of AT1R excretion in obese, relative to lean rats, may have implications for both BP and renal disease in the metabolic syndrome.

Interference of enalaprilat on glomerular permeability to macromolecules (IgG) in acute unilateral ureteral obstruction in rats

INTRODUCTION

Unilateral ureteral obstruction breaks out events that cause the transitory increase of glomerular permeability to macromolecules, both in the obstructed kidney and in the contralateral kidney, suggesting the presence of some factor, with a systemic action, liberated as a response to the obstruction. We know that the rennin-angiotensin system is activated by acute ureteral obstruction. We have developed an experiment to assess the role of angiotensin II on the glomerular permeability to IgG due to acute ureteral obstruction, using enalaprilat, an angiotensin enzyme conversion inhibitor, to block the effects of the activation of the rennin-angiotensin system.

MATERIALS AND METHODS

We have used 45 adult Wistar female rats, distributed into 3 main groups: a control group with 5 animals and 2 experiment groups each one with 10 animals submitted to unilateral ureteral obstruction and nephrectomy at 60 and 120 minutes. Each experiment group had its simulation correspondent (sham). We have studied both kidneys through the direct immunofluorescence method.

RESULTS

We have found positive permeation in animals without enalaprilat in both kidneys and negative permeation in those in which the drug was used.

CONCLUSION

We have concluded that enalaprilat interferes in this alteration of permeability, suggesting that angiotensin II is involved in the loss of selectivity of the glomerular membrane.

Glomerular hemodynamic changes associated with arteriolar lesions and tubulointerstitial inflammation

Glomerular hemodynamic adaptations to loss of renal mass are thought to be the initiating factor of progression to renal failure; however, tubulointerstitial (TI) injury correlates better with progression than with glomerular damage. Thus, it is conceivable that tubulointerstitial alterations participate in the pathophysiology of renal disease progression by modifying the adaptive responses of glomerular hemodynamics. In experimental models of progressive renal disease, suppressing tubulointerstitial inflammatory cell infiltration with anti-inflammatory drugs reduces renal damage despite persistence of systemic hypertension. In recent studies in rats with subtotal renal ablation, we found that treatment with polysulphate pentosan (PPS) and with mycophenolate mofetil (MMF) prevented proteinuria, glomerular hypertension, and hyperfiltration, despite persisting arterial hypertension due to higher afferent resistance. In addition, arteriolopathy was significantly attenuated by MMF, suggesting preservation of vascular structure and function. Association of vascular injury of afferent arterioles, glomerular hemodynamic changes, and renal lesions has been described in other conditions such as hyperuricemia, protein overload, fawn-hooded rats, and aging spontaneously hypertensive rats (SHR). Arteriolopathy results in a maladaptive function that permits the transmission of systemic hypertension to glomerular capillaries. Glomerular hypertension results in mechanical damage to the capillary wall and increased filtration of proteins to tubular lumen. Enhanced tubular reabsorption induces synthesis of proinflammatory and profibrotic factors, resulting in tubulointerstitial inflammation and fibrosis. In conditions in which there is overactivity of the renin-angiotensin system (RAS), such as mild hyperuricemia and protein overload, arteriolopathy is associated with increased glomerular pressure and reduced glomerular plasma flow that results in post-glomerular ischemia and tubulointerstitial injury.

Inflammation and angiotensin II

Angiotensin II (AngII), the major effector peptide of renin-angiotensin system (RAS), is now recognized as a growth factor that regulates cell growth and fibrosis, besides being a physiological mediator restoring circulatory integrity. In the last few years, a large number of experimental studies has further demonstrated that AngII is involved in key events of the inflammatory process. Here, we summarize the wide variety of AngII functions and discuss them in relation with the inflammatory cascade. AngII increases vascular permeability (via the release of prostaglandins and vascular endothelial cell growth factor or rearrangement of cytoskeletal proteins) that initiates the inflammatory process. AngII could contribute to the recruitment of inflammatory cells into the tissue through the regulation of adhesion molecules and chemokines by resident cells. Moreover, AngII could directly activate infiltrating immunocompetent cells, including chemotaxis, differentiation and proliferation. Recent data also suggest that RAS activation could play a certain role even in immunologically-induced inflammation. Transcriptional regulation, predominantly via nuclear factor-kappaB (NF-kappaB) and AP-1 activation, and second mediator systems, such as endothelin-1, the small G protein (Rho) and redox-pathways are shown to be involved in the molecular mechanism by which AngII exerts those functions. Finally, AngII participates in tissue repair and remodeling, through the regulation of cell growth and matrix synthesis. In summary, recent data support the hypothesis that RAS is key mediator of inflammation. Further understanding of the role of the RAS in this process may provide important opportunities for clinical research and treatment of inflammatory diseases.

Pathophysiology of proteinuria

Proteinuria is consequence of two mechanisms: the abnormal transglomerular passage of proteins due to increased permeability of glomerular capillary wall and their subsequent impaired reabsorption by the epithelial cells of the proximal tubuli. In the various glomerular diseases, the severity of disruption of the structural integrity of the glomerular capillary wall correlates with the area of the glomerular barrier being permeated by "large" pores, permitting the passage in the tubular lumen of high-molecular-weight (HMW) proteins, to which the barrier is normally impermeable. The increased load of such proteins in the tubular lumen leads to the saturation of the reabsorptive mechanism by the tubular cells, and, in the most severe or chronic conditions, to their toxic damage, that favors the increased urinary excretion of all proteins, including low-molecular-weight (LMW) proteins, which are completely reabsorbed in physiologic conditions. Recent clinical studies showed that in patients with glomerular diseases the urinary excretion of some HMW proteins [immunoglobulins G and M (IgG and IgM)] and of some LMW proteins, alpha1-microglobulin, beta2-microglobulin, correlates with the severity of the histologic lesions, and may predict, better than the quantity of proteinuria, the natural course, the outcome, and the response to treatment. It is suggested that some patients have already, at the time of clinical presentation, a structural damage of the glomerular capillary wall (injury of podocytes) and of the tubulointerstitium, the severity and scarce reversibility of which are reliably indicated by an elevated urinary excretion of HMW and LMW proteins.

Effects of combined ACE inhibitor and angiotensin II antagonist treatment in human chronic nephropathies

BACKGROUND

Proteinuria predicts renal disease progression, and its reduction by angiotensin-converting enzyme inhibitors (ACEi) or angiotensin II receptor antagonists (ARA) is renoprotective.

METHODS

In this prospective, randomized, cross-over study of 24 patients with nondiabetic, chronic nephropathies, we compared the effects on proteinuria, renal hemodynamics, and glomerular permselectivity of 8 weeks with comparable blood pressure control achieved by benazepril (10 mg/day) and valsartan (80 mg/day) combined therapy with those achieved by benazepril (20 mg/day) or valsartan (160 mg/day) alone.

RESULTS

Despite comparable changes in blood pressure and glomerular filtration rate (GFR), combined therapy decreased proteinuria more than benazepril (-56% vs. -45.9%, P=0.02) and valsartan (-41.5%, P=0.002). Changes in urinary protein to creatinine ratio followed the same trend. Filtration fraction and renal vascular resistances (RVR) decreased more with combined (-14.7%,-23.7%) or benazepril (-12.4%, -20.5%) than with valsartan (-2.7%, -12.5%, P < 0.05 vs. both). RVR changes, adjusted for GFR changes, were associated with those in proteinuria (P < 0.05). Changes in glomerular permeability were comparable and did not predict different changes in proteinuria in the three groups.

CONCLUSION

At comparable blood pressure, combined ACEi and ARA decreased proteinuria better than ACEi and ARA. The greater antiproteinuric effect most likely depended on an ACEi-related hemodynamic effect, in addition to glomerular size selectivity amelioration. Long-term combined ACEi and ARA therapy may be more renoprotective than treatment with each agent alone.

Amelioration by beraprost sodium, a prostacyclin analogue, of established renal dysfunction in rat glomerulonephritis model

Effects of beraprost sodium, a chemically stable prostacyclin analogue, on renal dysfunction in an experimental rat model of glomerulonephritis were investigated. Beraprost sodium (30, 100 and 300 microg/kg) was orally given twice daily from the late stage of nephritis in which renal dysfunction was already developed. Beraprost sodium treatment inhibited the increase in urinary protein, serum creatinine and blood urea nitrogen, and the decrease in creatinine clearance. The elevation of serum creatinine was also inhibited by predonisolone (1 mg/kg). However, captopril (25, 50 and 100 mg/kg) and dipyridamole (20 and 60 mg/kg) failed to inhibit the elevation of serum creatinine. In the beraprost sodium-treated nephritic rats, the increase in mRNA levels for monocyte chemoattractant protein-1 (MCP-1) and collagen in the kidney was inhibited. These results suggest that beraprost sodium ameliorates developed renal dysfunction and is possibly an effective agent for the treatment of human glomerulonephritis.

Renal handling of albumin: a critical review of basic concepts and perspective

Biochemical and physiological processes that underlie the mechanism of albuminuria are completely reassessed in this article in view of recent discoveries that filtered proteins undergo rapid degradation during renal passage and the resulting excreted peptide fragments are not detected by conventional urine protein assays. This means that filtered protein and/or albumin levels in urine have been seriously underestimated. The concept that albuminuria is a result of changes in glomerular permeability is questioned in light of these findings and also in terms of a critical examination of charge selectivity, shunts, or large-pore formation and hemodynamic effects. The glomerulus appears to function merely in terms of size selectivity alone, and for albumin, this does not change significantly in disease states. Intensive albumin processing by a living kidney occurs through cellular processes distal to the glomerular basement membrane. Failure of this cellular processing primarily leads to albuminuria. This review brings together recent data about urinary albumin clearance and current knowledge of receptors known to process albumin in both health and disease states. We conclude with a discussion of topical and controversial issues associated with the proposed new understanding of renal handling of albumin.

Structural determinants of glomerular permeability

Recent progress in relating the functional properties of the glomerular capillary wall to its unique structure is reviewed. The fenestrated endothelium, glomerular basement membrane (GBM), and epithelial filtration slits form a series arrangement in which the flow diverges as it enters the GBM from the fenestrae and converges again at the filtration slits. A hydrodynamic model that combines morphometric findings with water flow data in isolated GBM has predicted overall hydraulic permeabilities that are consistent with measurements in vivo. The resistance of the GBM to water flow, which accounts for roughly half that of the capillary wall, is strongly dependent on the extent to which the GBM surfaces are blocked by cells. The spatial frequency of filtration slits is predicted to be a very important determinant of the overall hydraulic permeability, in keeping with observations in several glomerular diseases in humans. Whereas the hydraulic resistances of the cell layers and GBM are additive, the overall sieving coefficient for a macromolecule (its concentration in Bowman's space divided by that in plasma) is the product of the sieving coefficients for the individual layers. Models for macromolecule filtration reveal that the individual sieving coefficients are influenced by one another and by the filtrate velocity, requiring great care in extrapolating in vitro observations to the living animal. The size selectivity of the glomerular capillary has been shown to be determined largely by the cellular layers, rather than the GBM. Controversial findings concerning glomerular charge selectivity are reviewed, and it is concluded that there is good evidence for a role of charge in restricting the transmural movement of albumin. Also discussed is an effect of albumin that has received little attention, namely, its tendency to increase the sieving coefficients of test macromolecules via steric interactions. Among the unresolved issues are the specific contributions of the endothelial glycocalyx and epithelial slit diaphragm to the overall hydraulic resistance and macromolecule selectivity and the nanostructural basis for the observed permeability properties of the GBM.

Pentosan polysulfate prevents glomerular hypertension and structural injury despite persisting hypertension in 5/6 nephrectomy rats

Five/six nephrectomy induces systemic and glomerular hypertension, glomerulosclerosis, proteinuria, and tubulointerstitial fibrosis. Polysulfate pentosan (PPS) decreases mesangial proliferation and extracellular matrix accumulation. The aim of this study was to determine whether PPS prevents glomerular hemodynamic changes and renal damage. Micropuncture studies were performed in three groups of eight male Wistar rats. Two groups included rats with 5/6 nephrectomy-one of which was treated with PPS in drinking water (100 mg/kg body wt) and the second of which received normal drinking water-and the third group consisted of normal rats that served as controls. Five/six nephrectomy produced systemic hypertension, a 50% reduction in GFR, and a 67% increase in single-nephron GFR due to elevated glomerular pressure and single-nephron plasma flow as well as proteinuria. Hypertension persisted in PPS-treated animals. Despite a similar reduction in GFR, PPS prevented the rise in single-nephron GFR, glomerular capillary hydrostatic pressure, and proteinuria. By morphometry, glomerular volume was increased by 46% and mesangial area by 94%. Fractional glomerular capillary area decreased by 24%. PPS prevented these changes. Tubular dilatation, epithelial cell atrophy, and increased interstitial area were largely prevented by PPS, as was the interstitial inflammatory infiltrate. These results suggest that the renal protection conferred by PPS was mediated both by prevention of glomerular hypertension as well as suppression of the inflammatory response. It was postulated that this was partly due to the preservation of a greater fraction of functional nephrons.

Microalbuminuria in essential hypertension: significance, pathophysiology, and therapeutic implications

Some patients with essential hypertension manifest greater than normal urinary albumin excretion (UAE). The significance of this association, which is the object of this review, is not well established. Hypertensive patients with microalbuminuria manifest greater levels of blood pressure, particularly at night, and higher serum levels of cholesterol, triglycerides, and uric acid than patients with normal UAE. Levels of high-density lipoprotein cholesterol, on the other hand, were lower in patients with microalbuminuria than in those with normal UAE. Patients with microalbuminuria manifested greater incidence of insulin resistance and thicker carotid arteries than patients with normal UAE. After a follow-up of 7 years, we observed that 12 cardiovascular events occurred among 54 (21.3%) patients with microalbuminuria and only two such events among 87 patients with normal UAE (P < 0.0002). Stepwise logistic regression analysis showed that UAE, cholesterol level, and diastolic blood pressure were independent predictors of the cardiovascular outcome. Rate of creatinine clearance from patients with microalbuminuria decreased more than that from those with normal UAE. In conclusion, these studies suggest that hypertensive individuals with microalbuminuria manifest a variety of biochemical and hormonal derangements with pathogenic potential, which results in hypertensive patients having a greater incidence of cardiovascular events and a greater decline in renal function than patients with normal UAE.

Effects of nonpeptide endothelin receptor antagonists in rats with reduced renal mass

This study was set up to evaluate the long-term effects of nonpeptide endothelin (ET) antagonists in rats with renal mass reduction (RMR). In the first series of experiments, rats were administered bosentan (100 mg/kg/day) or the angiotensin-converting enzyme inhibitor cilazapril (10 mg/kg/day) for 14 weeks beginning 24 h after RMR. As expected, cilazapril completely prevented the development of hypertension, proteinuria, and renal structural damage. In contrast, bosentan had no influence on the development of proteinuria and renal structural damage, although it had a moderate antihypertensive effect and improved creatinine clearance. A second set of experiments was performed to assess whether Ro 48-5695, a very potent ET antagonist optimized from bosentan, could prevent the development of renal damage and reverse established renal damage. Rats received Ro 48-5695 (30 mg/kg/day) beginning either 24 h (prevention) before for 8 weeks, or 4 weeks (reversal) after RMR. Ro 48-5695 attenuated the hypertension and the decline of creatinine clearance when treatment was started at 24 h, but not when started at 4 weeks. Ro 48-5695 had no effect on proteinuria. These observations suggest that ET-receptor activation does not play a major role in the progression of glomerular sclerosis in this model of chronic renal failure.

A subdepressor low dose of ramipril lowers urinary protein excretion without increasing plasma potassium

Angiotensin-converting enzyme (ACE) inhibitors are increasingly administered to patients with chronic renal disease. One issue of concern with the use of ACE inhibitors in patients with impaired renal function is the possible development of hyperkalemia. We reasoned that the impact of ACE inhibitors on plasma potassium could be minimized by administering these agents at very low doses. To examine this issue, we investigated the effect of a low dose of ramipril (1.25 mg orally once daily) and an eight-fold higher dose (10 mg orally once daily) on plasma potassium in 13 patients with proteinuria and mild chronic renal insufficiency. The study was divided into four phases: placebo (4 weeks), low-dose ramipril (8 weeks), high-dose ramipril (8 weeks), and washout phase (4 weeks). With the low dose of ramipril, urinary protein excretion decreased significantly as early as after 1 week of administration (from 4.4 +/- 0.5 to 3.7 +/- 0.4 g/24 h; P < 0.025) and did not decrease any further thereafter even when the dose was increased eight-fold. Mean arterial blood pressure and plasma potassium did not change significantly with the low dose of ramipril, whereas with the higher dose, mean arterial blood pressure decreased significantly (from 107 +/- 2.0 to 100 +/- 2.0 mm Hg, P < 0.005), and plasma potassium increased significantly (from 4.53 to 4.78 mEq/L, P < 0.05). We conclude that a low dose of ramipril can reduce proteinuria to the same extent as an eight-fold higher dose without significantly lowering blood pressure or increasing plasma potassium. This latter feature may be advantageous for the treatment of patients at risk for hyperkalemia who require ACE inhibitors.

ACE inhibition and ANG II receptor blockade improve glomerular size-selectivity in IgA nephropathy

Protein trafficking across the glomerular capillary has a pathogenic role in subsequent renal damage. Despite evidence that angiotensin-converting enzyme (ACE) inhibitors improve glomerular size-selectivity, whether this effect is solely due to ANG II blocking or if other mediators also play a contributory role is not clear yet. We studied 20 proteinuric patients with IgA nephropathy, who received either enalapril (20 mg/day) or the ANG II receptor blocker irbesartan (100 mg/day) for 28 days in a randomized double-blind study. Measurements of blood pressure, renal hemodynamics, and fractional clearance of neutral dextran of graded sizes were performed before and after 28 days of treatment. Both enalapril and irbesartan significantly reduced blood pressure over baseline. This reduction reached the maximum effect 4-6 h after drug administration but did not last for the entire 24-h period. Despite transient antihypertensive effect, proteinuria was effectively reduced by both treatments to comparable extents. Neither enalapril nor irbesartan modified the sieving coefficients of small dextran molecules, but both effectively reduced transglomerular passage of large test macromolecules. Theoretical analysis of sieving coefficients showed that neither drug affected significantly the mean pore radius or the spread of the pore-size distribution, but both importantly and comparably reduced the importance of a nonselective shunt pathway. These data suggest that antagonism of ANG II is the key mechanism by which ACE inhibitors exert their beneficial effect on glomerular size-selective function and consequently on glomerular filtration and urinary output of plasma proteins.

Fractional clearance of high molecular weight proteins in conscious rats using a continuous infusion method

BACKGROUND

The purported existence of "large pores" in the glomerular capillary wall has been derived primarily from studies using dextrans and Ficolls. Systematic studies using high molecular weight proteins have not been performed. One of the difficulties is that recent studies have demonstrated that albumin and other proteins undergo degradation during renal passage. Our study took into account this renal degradation in measuring the fractional clearance of various high molecular weight proteins (the hydrodynamic radii range was between 48 to 70 A).

METHODS

Fractional clearances of tritium-labeled proteins were measured using ALZET osmotic pumps, which are designed to release a slow continuous infusion of tracer. Blood and urine collections were taken at 24-hour intervals over seven days and were counted for radioactivity, and glomerular filtration rate was measured by a creatinine assay.

RESULTS

Steady-state levels of [3H]protein in plasma were obtained by day 6. The [3H]proteins in the plasma showed no degradation. The fractional clearances (mean +/- sd, N = 5) of the various proteins were albumin (radius = 36 A; 0.0023 +/- 0.0009), transferrin (48 A; 0.0046 +/- 0.0007), lactoperoxidase (58 A; 0. 0045 +/- 0.0005), immunoglobulin G (62 A; 0.0043 +/- 0.0009), lactate dehydrogenase (64 A; 0.0041 +/- 0.0009), and glucose oxidase (70 A; 0.0036 +/- 0.0011).

CONCLUSIONS

These values suggest a weak dependence of fractional clearance on size-selective filtration, except for albumin, which undergoes a specific type of postglomerular processing. The fractional clearances were higher than expected from previous data on dextrans and Ficolls of equivalent hydrodynamic radius, and thus demonstrate that "large pores" may already exist in normal glomerular capillary walls.

Glomerular charge selectivity for horseradish peroxidase and albumin at low and normal ionic strengths

The classical concept of a negative glomerular charge barrier has recently been questioned, mainly based on the somewhat high clearance for anionic horseradish peroxidase (HRP). The validity of using anionic HRP can be tested by changing the properties of the charge barrier. A rather unequivocal approach is to reduce the ionic composition of the perfusate and hence increase the Debye length. We determined the glomerular clearance for horseradish peroxidase and serum albumin, using isolated rat kidneys perfused at 8 degrees C to reduce the tubular modification of the primary urine. The perfusate contained trace amounts of the neutral 125I-nHRP and the anionic 131I-aHRP and were otherwise identical except for different ionic strengths, 152 mM and 34 mM, respectively. During control, the fractional clearance (theta) was 0.11 +/- 0.015 for nHRP and 0.045 +/- 0.010 for aHRP, with an average clearance ratio (n/a) of 2.8 +/- 0.24. Low ionic strength reduced theta for aHRP to 0.027 +/- 0.006, giving an increased clearance ratio for HRP of 4.2 +/- 0.44. The existence of a negative charge barrier is supported by the experiments. The result obtained during normal perfusion is compatible with a charge density (omega) of 34 mEq L-1, using a model of homogeneously charged membrane. Low ionic strength perfusion reversibly reduced the concentration of fixed charges to 12 mEq L-1, suggesting an almost threefold increase of the glomerular membrane volume. Thus, the glomerular charge barrier should be regarded to have a dynamic gel structure rather than being a rigid membrane.

Influence of angiotensin converting enzyme inhibition and angiotensin II type 1 receptor antagonism on renal sodium and water handling and albuminuria during infusion of atrial natriuretic factor into healthy volunteers

BACKGROUND

Atrial natriuretic factor increases urinary sodium and water excretion. It also causes an increase in albuminuria. Angiotensin converting enzyme inhibition attenuates the effects of atrial natriuretic factor on renal sodium and water handling; however, it is not known whether this effect is mediated by the accompanied decrease in blood pressure or by suppression of the renin-angiotensin system.

OBJECTIVE

To test the hypothesis that atrial natriuretic factor mediates natriuresis and diuresis by inhibiting angiotensin II, by studying the effects of the angiotensin converting enzyme inhibitor enalapril and the angiotensin II type 1 receptor antagonist losartan. In addition, the effects of these drugs on atrial natriuretic factor-induced albuminuria were examined.

DESIGN AND METHODS

We investigated the effects of enalapril and losartan on atrial natriuretic factor-induced changes in urinary excretion of sodium, water and albumin from eight healthy volunteers. Measurements of systemic and renal haemodynamics in these subjects were performed before and during a 2 h infusion of atrial natriuretic factor [0.01 microg/kg per min (low dose) for the first 60 min and 0.02 microg/kg per min (high dose) for the second 60 min]. Measurements were performed after 5 days of pretreatment with placebo, 50 mg losartan or 20 mg enalapril daily.

RESULTS

Mean arterial pressures during the clearance study were 84.6 +/- 1.7 mmHg after placebo, 84.0 +/- 2.2 mmHg after losartan treatment and 80.0 +/- 2.5 mmHg after enalapril treatment (P < 0.05). Plasma renin activity was significantly increased both by losartan and by enalapril treatments. Neither enalapril nor losartan treatment attenuated atrial natriuretic factor-induced changes in renal haemodynamics. After placebo pretreatment, fractional urinary excretion of sodium increased significantly during infusion of atrial natriuretic factor. Losartan treatment did not influence the increase in urinary excretion of sodium during infusion of atrial natriuretic factor, whereas enalapril treatment significantly attenuated this increase (P < 0.01). Atrial natriuretic factor significantly increased albuminuria. Neither losartan nor enalapril treatment reduced atrial natriuretic factor-induced albuminuria.

CONCLUSIONS

Enalapril treatment lowered blood pressure and attenuated the atrial natriuretic factor-induced increase in urinary excretion of sodium. In contrast, the angiotensin II type 1 receptor antagonist losartan, at a dosage that did not lower blood pressure, did not attenuate the increase in urinary excretion of sodium. These data indicate that atrial natriuretic factor increases natriuresis and diuresis independently of angiotensin II. The increase in albuminuria during infusion of atrial natriuretic factor was not influenced by enalapril and losartan treatments.

Acute renal effects of AT1-receptor blockade after exogenous angiotensin II infusion in healthy subjects

In 10 healthy normotensive volunteers on a normal sodium diet, we evaluated the renal effects of a single oral dose of 50 mg of irbesartan (SR 47436, BMS 186295), an angiotensin II AT1-receptor antagonist, in baseline conditions and during an exogenous angiotensin II infusion (2.5 ng/kg/min). We used a double-blind, placebo-controlled, crossover design. Hormones, blood pressure, renal hemodynamics, and urinary electrolytes were measured during each phase. To examine further the determinants of glomerular filtration at the microcirculation level, fractional clearance of neutral dextran was performed, and sieving curves were applied on a hydrodynamic model of ultrafiltration. Irbesartan administration was followed by an increase in active renin and plasma angiotensin II concentrations and renal plasma flow without change of systemic blood pressure, glomerular filtration rate, or plasma aldosterone concentration. Irbesartan did not affect either sieving curves or glomerular ultrafiltration determinants. Angiotensin II infusion at 2.5 ng/kg/min elicited a slight pressor response accompanied by a decrease in glomerular filtration rate and renal plasma flow and an enhancement of fractional dextran clearance over the radius range explored (3.4-5.4 nm). The transcapillary glomerular pressure gradient deltaP and the ultrafiltration coefficient kf were computed to increase by 9% and to decrease by 23%, respectively, without change in intrinsic membrane properties. Pretreatment with irbesartan prevented all these effects of angiotensin II.

Low dose angiotensin converting enzyme inhibition and glomerular permselectivity in renal transplant recipients

In this study, we determined the fractional clearance of neutral polydisperse dextrans (theta D) and monodisperse dextran sulfate (theta DS) to describe glomerular size and charge selectivity in 25 renal transplant recipients with proteinuria. Thirteen were treated with low dose lisinopril for six months (group 1) and 12 patients without ACE inhibitor therapy formed group 2. Mean arterial blood pressure was stable (group 1, 112 +/- 4; group 2, 109 +/- 2 mm Hg at baseline and after 6 months) whereas creatinine clearance, glomerular filtration rate and renal plasma flow decreased nonsignificantly but were comparable at any time. Lisinopril treatment lowered filtration fraction (22 +/- 2 vs. 19 +/- 2%, P = 0.07) whereas no change was seen in group 2 (20 +/- 2%). The fractional protein excretion (mg urinary protein per day/ml creatinine clearance per day) was stable in group 1, but significantly increased in group 2. The same pattern was found for theta D larger than 56 A. theta DS was stable and consistently elevated in both groups at any time. We conclude that low dose ACE inhibitor treatment in proteinuric renal transplant recipients stabilizes glomerular size selectivity independently of its systemic hemodynamic effects.

High glomerular permeability of bikunin despite similarity in charge and hydrodynamic size to serum albumin

Bikunin is a chondroitin-sulphate containing serum protein with a Stokes-Einstein radius and a negative net charge close to those of serum albumin. The plasma half life of bikunin is about 10 minutes, and approximately half of its clearance occurs in the kidneys. The quantitative role of glomerular filtration in the renal clearance of this protein has not been determined. To assess the glomerular permeability of bikunin we used isolated rat kidneys that were perfused with an albumin solution. The metabolic activities of the tubuli were inhibited by low temperature (8 degrees C). The clearances of radiolabeled bikunin and albumin were repeatedly determined under identical conditions. The fractional clearance of bikunin was found to be 80 times higher than that of albumin: 15% +/- 1% versus 0.18% +/- 0.02%. This value for bikunin can fully account for its renal clearance in vivo. It has previously been shown that uncharged flexible solutes, such as dextrans, have higher renal clearances than globular molecules with similar radii. The high glomerular permeability of bikunin is therefore probably due to its elongated and flexible configuration. Moreover, the observed clearance value of the anionic molecule bikunin is close to that of a neutral flexible dextran of similar size, indicating that the charge of bikunin is of little importance for its glomerular permeability.

Effects of losartan on renal function in patients with essential hypertension

We examined the renal hemodynamic modifications induced by a selective angiotensin II (AII) AT1 receptor antagonist, losartan, in 10 patients with essential hypertension. In this single-blind study, renal hemodynamic parameters were determined twice (patients were their own controls) first after a 15-day single-blind placebo run-in period and again after a 1-month losartan period. The dosage of losartan was 50 mg/day. Glomerular filtration rate (GFR, inulin clearance), renal plasma flow [RPF; para-aminohippurate (PAH) clearance], microalbuminuria, sodium excretion, proximal sodium tubular reabsorption (lithium clearance), and acid uric metabolism were measured. After 1-month losartan treatment, systolic and diastolic BP (SBP, DBP) decreased significantly throughout the 210-min recording whereas heart rate (HR) was unchanged. GFR (100 +/- 19 vs. 96 +/- 17 ml/min/1.73 m2) and RPF (471 +/- 118 vs. 468 +/- 108 ml/ min/1.73 m2) were not altered by losartan. Rather than occurrence of any modification in filtration fraction (FF), a significant decrease in microalbuminuria was evident (57 +/- 77 vs. 40 +/- 59 mg/24 h, p < 0.05). Urinary sodium excretion was not modified, but an almost significant (p = 0.07) decrease in proximal sodium reabsorption was observed (72.9 +/- 7.7 vs. 68.1 +/- 6.4% of filtered sodium). The increase in renal uric clearance accounted for the significant decrease in serum uric acid (195 +/- 49 vs. 183 +/- 43 microM; p < 0.05). After 1-month losartan treatment, renal function was well preserved; the decrease in uric acid may be of clinical interest when adjuvent diuretic therapy is required.

Renal function and glomerular permselectivity late after living related donor transplantation

Living related kidney transplantation is the preferable procedure for renal replacement therapy. The aim of the current study was to determine systemic hemodynamic and intrarenal adaptions in donors and recipients late after living related kidney transplantation. Furthermore, glomerular permselectivity was assessed in these subjects. We studied mean blood pressure (MAP), glomerular filtration rate (GFR), renal plasma flow (RPF), microalbuminuria (MIA), 24-hr urinary protein excretion, and glomerular permselectivity (fractional clearance of neutral dextrans [thetaD] as a marker for size selectivity and fractional clearance of dextran sulfate [thetaDS] to assess charge selectivity) in 22 donors and 22 recipients. MAP was normal in the donor group (102 +/- 4 mmHg), but five patients had blood pressure above 140/90 mmHg. This 18%, however, is lower than the prevalence of hypertension in the age-adjusted general population in Austria. The recipients also had normal MAP at the time of study (99 +/- 3); however, 13 needed antihypertensive therapy. GFR and RPF were lower in recipients than in donors (53 +/- 8 vs. 72 +/- 11 and 314 +/- 74 vs. 412 +/- 86 ml/min respectively). In the donor group, GFR was 137 +/- 45% of the expected age-adjusted mean value/kidney due to hyperfiltration. Proteinuria and MIA were higher in the recipients than in the donors (0.39 +/- 0.22 vs. 0.07 +/- 0.04 g/day, 137 +/- 136 vs. 26 +/- 15 mg/day). Nonetheless, five donors had an elevated MIA. A higher need for antihypertensive medication could be observed in recipients with previous rejection episodes, as well as a significantly higher urinary protein excretion and MIA (0.7 +/- 0.42 vs. 0.24 +/- 0.14 g/day, 336 +/- 380 vs. 48 +/- 32 mg/day). ThetaDS was significantly higher in the recipients, whereas thetaDS of the donors was identical to the value obtained from 18 healthy controls (0.7 +/- 0.08 vs. 0.6 +/- 0.06). OD was similar in all groups studied. In conclusion, 76 months after uninephrectomy for renal donation, mild changes in glomerular permselectivity occurred in a subset of donors without affecting renal excretory function. In recipients, proteinuria was due to a defect in glomerular charge selectivity.

Circadian rhythm in glomerular transport of macromolecules through large pores and shunt pathway

In previous studies we have demonstrated that the circadian rhythm in renal clearance of serum proteins is more pronounced than the variability in glomerular filtration rate, and that the highest day-night fluctuations are found for the largest proteins. To analyze whether additional circadian rhythmicity in size-selective glomerular transport could explain these phenomena, we measured renal clearances of inulin and dextrans in a range of 30 to 90 A over a period of one day and compared these data with renal clearance in proteins. Eight patients with nephrotic syndrome and a GFR > 60 ml/min and 6 healthy volunteers were studied during a protocol of bed rest and spaced protein and fluid intake. After administration of a loading dose, inulin and dextran were continuously infused. Blood and urine were sampled every three hours. In patients, but not in normals, fractional clearances of dextrans larger than 45 A showed a circadian rhythm with a peak in daytime and a close phase-relationship with the rhythm in GFR. The day-night differences were the most pronounced for the largest dextrans. Analysis of the day-night differences in a computer model showed circadian variability in transport through the shunt pathway and through large pores. These results can, to an important degree, explain our previous observations on circadian variability in renal clearance of proteins in patients with nephrotic syndrome.

ACE inhibition reduces proteinuria, glomerular lesions and extracellular matrix production in a normotensive rat model of immune complex nephritis

We studied the effect of the angiotensin converting enzyme (ACE) inhibitor, quinapril, on the clinical and morphological lesions of a normotensive model of immune complex nephritis. Untreated rats developed massive nephrotic syndrome, intense cell proliferation and glomerular and tubulointerstitial lesions. In the renal cortex of nephritic rats there was a significant increase in gene expression of TGF-beta 1, fibronectin and collagens, and ACE activity. Systolic blood pressure remained normal with progression of the disease. Administration of quinapril for three weeks to animals with glomerular lesions (proteinuria 20 to 50 mg/day) avoided the development of intense proteinuria (79 +/- 28 vs. 589 +/- 73 mg/day, P < 0.001) and decreased cell proliferation, glomerulosclerosis, tubulointerstitial lesions, and inflammatory infiltrates. Cortical gene expression of TGF-beta 1 and matrix proteins was also diminished. ACE activity was inhibited by 68% in renal cortex. These results show that quinapril administration to normotensive rats with immune complex nephritis decreases proteinuria and glomerular and tubulointerstitial lesions, probably modulating the local angiotensin II generation and its effects on cell growth, TGF beta and matrix protein synthesis.

Renal circulation and blockade of the renin-angiotensin system. Is angiotensin-converting enzyme inhibition the last word?

The mechanism by which angiotensin-converting enzyme (ACE) inhibition influences renal perfusion and function has assumed growing importance as alternatives for blocking the system have emerged. Neither renin inhibitors nor angiotensin II (Ang II) antagonists are likely to trigger responses similar to ACE inhibitor-induced involvement of kinins, prostaglandins, or nitric oxide. Several observations suggest species variation in the contribution of these pathways to the renal response to ACE inhibition. In humans, recent investigation suggests that virtually all of the renal response is due to a fall in Ang II formation. Perhaps most persuasive is the surprising observation that the renal hemodynamic response to renin inhibitors exceeds by more than 50% the response to ACE inhibition in healthy humans. To the extent that kinins or prostaglandins contribute to the renal response to ACE inhibition, one would anticipate a smaller response to renin inhibition. Possible explanations include an unanticipated additional action of renin inhibitors, better tissue penetration of these highly lipophilic agents, or more effective blockade of Ang II formation through an action at the rate-limiting step or non-ACE-dependent Ang II generation. Substantial evidence favors the latter two possibilities. Whatever the explanation, these observations raise the intriguing possibility that the undoubted therapeutic efficacy of ACE inhibition in renal injury, documented most rigorously for type I diabetes mellitus, might be exceeded with the newer classes of agent.

Endothelial cell injury initiates glomerular sclerosis in the rat remnant kidney

The development of progressive glomerulosclerosis in the renal ablation model has been ascribed to a number of humoral and hemodynamic events, including the peptide growth factor, transforming growth factor-beta 1 (TGF-beta 1). An important role has also been attributed to angiotensin II (AII), which, in addition to its hemodynamic effects, can stimulate transcription of TGF-beta 1. We postulated that increased glomerular production of AII, resulting from enhanced intrinsic angiotensinogen expression, stimulates local TGF-beta 1 synthesis, activating glomerular matrix protein synthesis, and leads to sclerosis. Using in situ reverse transcription, the glomerular cell sites of alpha-1 (IV) collagen, fibronectin, laminin B1, angiotensinogen, and TGF-beta 1 mRNA synthesis were determined at sequential periods following renal ablation. The early hypertrophic phase was associated with global, but transient, increases in the mRNA for alpha-1 (IV) collagen. No changes were noted for fibronectin, TGF-beta 1, and angiotensinogen mRNAs. At 24 d after ablation, at which time sclerosis is not evident, endothelial cells, particularly in the dilated capillaries at the vascular pole, expressed angiotensinogen and TGF-beta 1 mRNAs, as well as fibronectin and laminin B1 RNA transcripts. By 74 d after ablation angiotensinogen and TGF-beta 1 mRNAs were widely distributed among endothelial and mesangial cells, and were particularly prominent in regions of evolving sclerosis. These same regions were also notable for enhanced expression of matrix protein mRNAs, particularly fibronectin. All receptor blockade inhibited angiotensinogen, TGF-beta 1, fibronectin, and laminin B1 mRNA expression by the endothelium. We conclude that, as a result of hemodynamic changes, injured or activated endothelium synthesizes angiotensinogen, triggering a cascade of TGF-beta 1 and matrix protein gene expression with resultant development of the segmental glomerular sclerotic lesion.

Glomerular permselectivity in proteinuric patients after kidney transplantation

To characterize the defect in glomerular permselectivity responsible for proteinuria after renal transplantation, we studied 10 patients with moderate proteinuria (median 0.37 g/d, range 0.20-0.79), 16 patients with the nephrotic syndrome (6.73 g/d, 3.9-14.6), 8 living related donor transplant recipients without any history of rejection (median proteinuria 0.26 g/d, 0.06-0.58), and 12 healthy volunteers. The fractional clearance of neutral dextrans > 54 A was significantly higher in nephrotic patients, demonstrating a defect in glomerular size selectivity. Using a log-normal model of glomerular pore size distribution, r*(5%) and r*(1%), indices for the presence of large pores, were increased in the nephrotic patients. The fractional clearance of negatively charged dextran sulfate was significantly higher in all patient groups, indicating a loss of glomerular charge selectivity. Biopsy findings showed more prominent glomerular lesions in the nephrotic group compared with the moderately proteinuric group. We conclude that mild proteinuria late after renal transplantation is associated with a defect in glomerular charge selectivity. The development of nephrotic range proteinuria is associated also with a defect of glomerular size selectivity, which correlates with prominent glomerular pathology.

ACE inhibition prevents renal failure and death in uninephrectomized MWF/Ztm rats

Many studies have consistently documented that angiotensin converting enzyme (ACE) inhibitors prevent proteinuria and glomerulosclerosis in progressive renal disease, but very few data are available on whether they also prevent renal failure and death. The mechanisms of the beneficial effect of ACE inhibition are only partially understood. Recent data suggest that angiotensin II modulates renal synthesis of endothelin-1, a vasoactive peptide implicated in the process of renal injury. Here we investigated in a long-term study whether ACE inhibition ameliorated renal function in uninephrectomized (UNx) male MWF/Ztm rats. Three groups of rats at nine weeks of age underwent UNx or sham-operation. Nephrectomized animals were left untreated or treated with the ACE inhibitor lisinopril in drinking water. In untreated UNx animals systolic blood pressure, serum creatinine, urinary protein and renal synthesis of endothelin-1, evaluated by its urinary excretion, were significantly increased, as compared with control animals with two kidneys. End-stage renal failure developed in all untreated UNx rats that died within 9 to 14 months from UNx. ACE inhibitor significantly reduced systolic blood pressure, completely prevented proteinuria and renal function deterioration, and reduced endothelin-1 excretion. All UNx rats treated with lisinopril were alive 14 months after UNx. These results show that ACE inhibition prevents end-stage renal failure induced by UNx in male MWF/Ztm, and that the beneficial effects of angiotensin II inhibition in this model are related to modulation of renal synthesis of endothelin-1.

The effect of acute angiotensin II blockade on renal function in rats with reduced renal mass

The effect of acute Ang II blockade on renal function in rats with reduced nephron number was assessed in micropuncture studies. The Ang II receptor blocker, losartan, was administered at a dose of 10 mg i.v. at two intervals following five-sixths renal ablation. At eight weeks following ablation, Ang II blockade (Ang IIX) increased sodium excretion [UNa V, Ang IIX 2.2 +/- 0.4 microEq/min; time control (TC) 1.0 +/- 0.3 microEq/min; P < 0.05] but did not reduce mean arterial pressure (AP, Ang IIX 142 +/- 6 mm Hg; TC 151 +/- 6 mmHg), glomerular transcapillary pressure (delta P, Ang IIX 50 +/- 1 mm Hg; TC 50 +/- 1 mm Hg), or urine albumin excretion (UAlb V: Ang IIX 149 +/- 18 micrograms/min; TC 168 +/- 20 micrograms/min). Similarly, at two weeks following ablation, Ang II blockade increased UNa V (Ang IIX 2.8 +/- 0.4 microEq/min; TC 0.5 +/- 0.2 microEq/min; P < 0.05) without reducing AP (Ang IIX 132 +/- 6 mm Hg; TC 140 +/- 7 mm Hg), delta P (Ang IIX 50 +/- 3 mm Hg; TC 48 +/- 2 mm Hg), or UAlb V (Ang IIX 32 +/- 3 micrograms/min; TC 36 +/- 10 micrograms/min). These findings indicate that within the remant kidney, Ang II promotes sodium retention but does not have an acutely reversible effect on glomerular pressure or permselectivity.

Charge selectivity of the glomerular filtration barrier in healthy and nephrotic humans

We used dextran sulfate (DS) to evaluate barrier charge selectivity in 11 nonproteinuric subjects and in 11 patients with the nephrotic syndrome due to either membranous nephropathy or minimal change nephropathy. The 3H-DS preparation spanned a molecular radius interval of 10-24 A and exhibited size-dependent protein binding in vitro. Urine and ultrafiltrates of plasma were separated by size into narrow fractions using gel permeation chromatography. The sieving coefficient (theta) for ultrafilterable DS of 15A radius averaged 0.68 +/- 0.03 in nonproteinuric vs. 0.95 +/- 0.05 in nephrotic subjects (P < 0.001). Uncharged dextrans of broad size distribution were used to evaluate barrier size-selectivity in separate groups of nonproteinuric subjects (n = 19) and nephrotic patients with either minimal change (n = 20) or membranous nephropathy (n = 27). The value of theta for an uncharged dextran of similarly small radius (approximately 18 A) was significantly larger than that observed for DS in nonproteinuric subjects, but was similar in nephrotic individuals. Further, impaired barrier size-selectivity, as assessed by the sieving profile for uncharged dextrans (18-60 A radius), failed to account fully for the observed level of albuminuria in almost half of the patients with either minimal change (9/20) or membranous nephropathy (12/27). Together these findings suggest that the human glomerular capillary wall normally provides an electrostatic barrier to filtration of negatively charged macromolecules such as albumin, and that impairment of this electrostatic barrier contributes to the magnitude of albuminuria in the nephrotic syndrome.

Inhibitory effect of a novel antianginal agent, E4080, on ST segment elevation induced by vasopressin in anesthetized guinea pigs

We compared the antianginal effect of E4080, a novel bradycardiac agent with coronary vasodilating properties, with those of a bradycardiac agent and some coronary vasodilators in vasopressin-induced anginal model of guinea pigs. An i.v.-administration of vasopressin (0.2 IU/kg) produced an ST segment elevation on electrocardiograms (ECG) of 0.30 +/- 0.05 mV from the baseline within 30 sec in anesthetized guinea pigs. The ST segment elevation on ECG was used as an index of myocardial ischemia. E4080 and other drugs were injected i.v. 5 min before the administration of vasopressin. E4080 at 5 mg/kg depressed the ST segment elevation induced by vasopressin to 0.06 +/- 0.01 mV (20% of control, n = 6, P < 0.001). However, alinidine (5 mg/kg), which produced the same bradycardic action (reduction of heart rate by 50%) as that of E4080, tended to inhibit the ST segment elevation, but this was not statistically significant. On the other hand, other vasodilators such as isosorbide dinitrate (0.3 mg/kg), nifedipine (0.1 mg/kg) and lemakalim (1 mg/kg) also significantly reduced the ST segment elevation to 0.16 +/- 0.03, 0.08 +/- 0.04 and 0.09 +/- 0.03 mV, respectively. These results suggest that the inhibitory effect of E4080 on the ST segment elevation induced by vasopressin is due to the coronary vasodilating effect rather than the bradycardiac effect, and that E4080 would be useful as an antianginal agent.