Dynamics of glomerular ultrafiltration in the rat. IV. Determination of the ultrafiltration coefficient

The Role of P2X7 Purinergic Receptors in the Renal Inflammation Associated with Angiotensin II-induced Hypertension

Purinergic receptors play a central role in the renal pathophysiology of angiotensin II-induced hypertension, since elevated ATP chronically activates P2X7 receptors in this model. The changes induced by the P2X antagonist Brilliant blue G (BBG) in glomerular hemodynamics and in tubulointerstitial inflammation resulting from angiotensin II infusion were studied. Rats received angiotensin II (435 ng·kg^-1·min^-1, 2 weeks) alone or in combination with BBG (50 mg/kg/day intraperitoneally). BBG did not modify hypertension (214.5 ± 1.4 vs. 212.7 ± 0.5 mmHg), but restored to near normal values afferent (7.03 ± 1.00 to 2.97 ± 0.27 dyn.s.cm^-5) and efferent (2.62 ± 0.03 to 1.29 ± 0.09 dyn.s.cm^-5) arteriolar resistances, glomerular plasma flow (79.23 ± 3.15 to 134.30 ± 1.11 nl/min), ultrafiltration coefficient (0.020 ± 0.002 to 0.036 ± 0.003 nl/min/mmHg) and single nephron glomerular filtration rate (22.28 ± 2.04 to 34.46 ± 1.54 nl/min). Angiotensin II induced overexpression of P2X7 receptors in renal tubular cells and in infiltrating T and B lymphocytes and macrophages. All inflammatory cells were increased by angiotensin II infusion and reduced by 20% to 50% (p < 0.05) by BBG administration. Increased IL-2, IL-6, TNFα, IL-1β, IL-18 and overexpression of NLRP3 inflammasome were induced by angiotensin II and suppressed by BBG. These studies suggest that P2X7 receptor-mediated renal vasoconstriction, tubulointerstitial inflammation and activation of NLRP3 inflammasome are associated with angiotensin II-induced hypertension.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Longitudinal study of living kidney donor glomerular dynamics after nephrectomy

BACKGROUND

Over 5,000 living kidney donor nephrectomies are performed annually in the US. While the physiological changes that occur early after nephrectomy are well documented, less is known about the long-term glomerular dynamics in living donors.

METHODS

We enrolled 21 adult living kidney donors to undergo detailed long-term clinical, physiological, and radiological evaluation pre-, early post- (median, 0.8 years), and late post- (median, 6.3 years) donation. A morphometric analysis of glomeruli obtained during nephrectomy was performed in 19 subjects.

RESULTS

Donors showed parallel increases in single-kidney renal plasma flow (RPF), renocortical volume, and glomerular filtration rate (GFR) early after the procedure, and these changes were sustained through to the late post-donation period. We used mathematical modeling to estimate the glomerular ultrafiltration coefficient (Kf), which also increased early and then remained constant through the late post-donation study. Assuming that the filtration surface area (and hence, Kf) increased in proportion to renocortical volume after donation, we calculated that the 40% elevation in the single-kidney GFR observed after donation could be attributed exclusively to an increase in the Kf. The prevalence of hypertension in donors increased from 14% in the early post-donation period to 57% in the late post-donation period. No subjects exhibited elevated levels of albuminuria.

CONCLUSIONS

Adaptive hyperfiltration after donor nephrectomy is attributable to hyperperfusion and hypertrophy of the remaining glomeruli. Our findings point away from the development of glomerular hypertension following kidney donation.

TRIAL REGISTRATION

Not applicable. FUNDING. NIH (R01DK064697 and K23DK087937); Astellas Pharma US; the John M. Sobrato Foundation; the Satellite Extramural Grant Foundation; and the American Society of Nephrology.

Renal adaptation during hibernation

Hibernators periodically undergo profound physiological changes including dramatic reductions in metabolic, heart, and respiratory rates and core body temperature. This review discusses the effect of hypoperfusion and hypothermia observed during hibernation on glomerular filtration and renal plasma flow, as well as specific adaptations in renal architecture, vasculature, the renin-angiotensin system, and upregulation of possible protective mechanisms during the extreme conditions endured by hibernating mammals. Understanding the mechanisms of protection against organ injury during hibernation may provide insights into potential therapies for organ injury during cold storage and reimplantation during transplantation.

Endothelial glycocalyx dysfunction in disease: albuminuria and increased microvascular permeability

Appreciation of the glomerular microcirculation as a specialized microcirculatory bed, rather than as an entirely separate entity, affords important insights into both glomerular and systemic microvascular pathophysiology. In this review we compare regulation of permeability in systemic and glomerular microcirculations, focusing particularly on the role of the endothelial glycocalyx, and consider the implications for disease processes. The luminal surface of vascular endothelium throughout the body is covered with endothelial glycocalyx, comprising surface-anchored proteoglycans, supplemented with adsorbed soluble proteoglycans, glycosaminoglycans and plasma constituents. In both continuous and fenestrated microvessels, this endothelial glycocalyx provides resistance to the transcapillary escape of water and macromolecules, acting as an integral component of the multilayered barrier provided by the walls of these microvessels (ie acting in concert with clefts or fenestrae across endothelial cell layers, basement membranes and pericytes). Dysfunction of any of these capillary wall components, including the endothelial glycocalyx, can disrupt normal microvascular permeability. Because of its ubiquitous nature, damage to the endothelial glycocalyx alters the permeability of multiple capillary beds: in the glomerulus this is clinically apparent as albuminuria. Generalized damage to the endothelial glycocalyx can therefore manifest as both albuminuria and increased systemic microvascular permeability. This triad of altered endothelial glycocalyx, albuminuria and increased systemic microvascular permeability occurs in a number of important diseases, such as diabetes, with accumulating evidence for a similar phenomenon in ischaemia-reperfusion injury and infectious disease. The detection of albuminuria therefore has implications for the function of the microcirculation as a whole. The importance of the endothelial glycocalyx for other aspects of vascular function/dysfunction, such as mechanotransduction, leukocyte-endothelial interactions and the development of atherosclerosis, indicate that alterations in the endothelial glycocalyx may also be playing a role in the dysfunction of other organs observed in these disease states.

Contribution of renal purinergic receptors to renal vasoconstriction in angiotensin II-induced hypertensive rats

To investigate the participation of purinergic P2 receptors in the regulation of renal function in ANG II-dependent hypertension, renal and glomerular hemodynamics were evaluated in chronic ANG II-infused (14 days) and Sham rats during acute blockade of P2 receptors with PPADS. In addition, P2X1 and P2Y1 protein and mRNA expression were compared in ANG II-infused and Sham rats. Chronic ANG II-infused rats exhibited increased afferent and efferent arteriolar resistances and reductions in glomerular blood flow, glomerular filtration rate (GFR), single-nephron GFR (SNGFR), and glomerular ultrafiltration coefficient. PPADS restored afferent and efferent resistances as well as glomerular blood flow and SNGFR, but did not ameliorate the elevated arterial blood pressure. In Sham rats, PPADS increased afferent and efferent arteriolar resistances and reduced GFR and SNGFR. Since purinergic blockade may influence nitric oxide (NO) release, we evaluated the role of NO in the response to PPADS. Acute blockade with N(ω)-nitro-l-arginine methyl ester (l-NAME) reversed the vasodilatory effects of PPADS and reduced urinary nitrate excretion (NO(2)(-)/NO(3)(-)) in ANG II-infused rats, indicating a NO-mediated vasodilation during PPADS treatment. In Sham rats, PPADS induced renal vasoconstriction which was not modified by l-NAME, suggesting blockade of a P2X receptor subtype linked to the NO pathway; the response was similar to that obtained with l-NAME alone. P2X1 receptor expression in the renal cortex was increased by chronic ANG II infusion, but there were no changes in P2Y1 receptor abundance. These findings indicate that there is an enhanced P2 receptor-mediated vasoconstriction of afferent and efferent arterioles in chronic ANG II-infused rats, which contributes to the increased renal vascular resistance observed in ANG II-dependent hypertension.

Renal ultrafiltration changes induced by focused US

PURPOSE

To determine if focused ultrasonography (US) combined with a diagnostic microbubble-based US contrast agent can be used to modulate glomerular ultrafiltration and size selectivity.

MATERIALS AND METHODS

The experiments were approved by the animal care committee. The left kidney of 17 healthy rabbits was sonicated by using a 260-kHz focused US transducer in the presence of a microbubble-based US contrast agent. The right kidney served as the control. Three acoustic power levels were applied: 0.4 W (six rabbits), 0.9 W (six rabbits), and 1.7 W (five rabbits). Three rabbits were not treated with focused US and served as control animals. The authors evaluated changes in glomerular size selectivity by measuring the clearance rates of 3000- and 70,000-Da fluorescence-neutral dextrans. The creatinine clearance was calculated for estimation of the glomerular filtration rate. The urinary protein-creatinine ratio was monitored during the experiments. The authors assessed tubular function by evaluating the fractional sodium excretion, tubular reabsorption of phosphate, and gamma-glutamyltransferase-creatinine ratio. Whole-kidney histologic analysis was performed. For each measurement, the values obtained before and after sonication were compared by using the paired t test.

RESULTS

Significant (P < .05) increases in the relative (ratio of treated kidney value/nontreated kidney value) clearance of small- and large-molecule agents and the urine flow rates that resulted from the focused US treatments were observed. Overall, 1.23-, 1.23-, 1.61-, and 1.47-fold enhancement of creatinine clearance, 3000-Da dextran clearance, 70 000-Da dextran clearance, and urine flow rate, respectively, were observed. Focal tubular hemorrhage and transient functional tubular alterations were observed at only the highest (1.7-W) acoustic power level tested.

CONCLUSION

Glomerular ultrafiltration and size selectivity can be temporarily modified with simultaneous application of US and microbubbles. This method could offer new opportunities for treatment of renal disease.

Micropuncturing the nephron

To achieve the role of the kidney in maintaining body homeostasis, the renal vasculature, the glomeruli, and the various segments of the nephron and the collecting duct system have to fulfill very diverse and specific functions. These functions are dependent on a complex renal architecture and are regulated by systemic hemodynamics, hormones, and nerves. As a consequence, to better understand the physiology of the kidney, methods are necessary that allow insights on the function of these diverse structures in the physiological context of the intact kidney. The renal micropuncture technique allows direct access to study superficial nephrons in vivo. In this review, the application of micropuncture techniques on the single nephron level is outlined as an approach to better understand aspects of glomerular filtration, tubular transport, and tubulo-glomerular communication. Studies from the author's lab, including experiments in gene-targeted mice, are briefly presented to illustrate some of the approaches and show how they can further advance our understanding of the molecular mechanisms involved in the regulation of kidney function.

Renal interstitial adenosine is increased in angiotensin II-induced hypertensive rats

Since marked renal vasoconstriction is observed in angiotensin II (ANG II)-mediated hypertensive rats, we studied the possible interaction between ANG II and adenosine in this model. ANG II was infused into male Wistar rats through osmotic minipumps (435 ng·kg−1·min−1) for 14 days. In sham and ANG II groups, renal tissue and interstitial adenosine were measured; both increased to a similar twofold extent in the ANG II-treated rats (31.40 ± 4 vs. 62.0 ± 8.4 nM, sham vs. ANG II, interstitial adenosine; P< 0.001). The latter decreased by 47% with the specific blockade of 5′-nucleotidase. Glomerular hemodynamics demonstrated marked renal vasoconstriction in the angiotensin-treated group, which was reverted by an adenosine A1-receptor antagonist (8-cyclopentyl-1,3-dipropylxanthine, 10 μg·kg−1·min−1). 5′-Nucleotidase and adenosine deaminase (ADA) activities were measured in the cytosolic and membrane fractions. Only the membrane ADA activity decreased from 1,202 ± 80 to 900 ± 50 mU/mg protein in the ANG II-treated rats ( P< 0.05), as well as in their protein and mRNA expression. Despite the adenosine elevation, A1and A2breceptor protein did not change; in contrast, downregulation was observed in A2areceptor and upregulation in A3receptor. A similar pattern was found in the cortex and in the medulla; mRNA significantly decreased only in the A3receptor in both segments. These results suggest that the elevation of renal tissue and interstitial adenosine contributes to the renal vasoconstriction observed in the ANG II-induced hypertension and that it is mediated by a decrease in the activity and expression of ADA, increased production of adenosine, and an induced imbalance in adenosine receptors.

Angiotensin II, interstitial inflammation, and the pathogenesis of salt-sensitive hypertension

Transient administration of ANG II causes persistent salt-sensitive hypertension associated with arteriolopathy, interstitial inflammation, and cortical vasoconstriction; blocking the vascular and inflammatory changes with mycophenolate mofetil (MMF) prevents vasoconstriction. While infiltrating leukocytes during the salt-sensitive hypertension phase express ANG II, the functional role of ANG II during this phase is not known. We examined the acute effect of candesartan on renal hemodynamics during the established salt-sensitive hypertensive phase and related these findings to direct measurement of intrarenal ANG II and inflammatory cells in rats previously exposed to ANG II with or without MMF treatment. Sham controls were also examined. The administration of ANG II, followed by exposure to high-salt diet, resulted in hypertension, cortical vasoconstriction, an increase in interstitial inflammatory cells (44.8 +/- 1.3 lymphocytes/mm2, and 30.8 +/- 1.2 macrophages/mm2 ANG II vs. 19.6 +/- 2 lymphocytes/mm2, and 22 +/- 0.7 macrophages/mm2 Sham), and increase in renal ANG II levels (1,358 +/- 74.6 pg/ml ANG II vs. 194 +/- 9.28 pg/ml Sham). Treatment with MMF during the administration of exogenous ANG II resulted in reduction in renal interstitial inflammation (19.7 +/- 0.9 lymphocytes/mm2 and 15.9 +/- 0.8 machophages/mm2), ANG II levels (436.9 +/- 52.29 pg/ml), cortical vasoconstriction, and stable blood pressure levels during the subsequent challenge with a high-salt diet. Acute administration of candesartan similarly reduced renal vasoconstriction and blood pressure. We conclude that the cortical vasoconstriction occurring with salt-sensitive hypertension following exposure to ANG II is mediated by intrarenal ANG II, related, at least in part, to the interstitial inflammation.

Effects of Reactive Oxygen Species on in vitro Filtration of Water and Albumin across Glomerular Basement Membrane

Most of the interest in the glomerular basement membrane (GBM) stems from the observation that it undergoes morphological changes in renal disease. Studies on persistent proteinuria in experimental animal models have shown that the permeability properties of the GBM have been altered as a result of protein degradation and cross-linking of type IV collagen via its NC1 domains promoted by reactive oxygen species (ROS) and extrusion of tubular cell contents. We used the in vitro ultrafiltration technique to assess permeability properties of bare isolated GBM films to water and albumin in the Munich Wistar Fromter rat model of glomerular injury. Hydraulic permeability for water and albumin solutions and albumin fractional clearances were measured for rats treated with lisinopril [an angiotensin converting enzyme (ACE) inhibitor] and were compared with those measured for rats treated with dimethylthiouria (an ROS scavenger) and their control groups, at four pressure levels (50, 100, 200, and 300 mmHg). The ACE inhibitors and ROS scavengers treatment regimens for studied rats in addition to significantly lowering their systolic blood pressure and urinary protein excretion values to normal levels, have significantly increased their in vitro hydraulic and Darcy permeability, which is a measure of the intrinsic hydraulic conductance of the GBM, either in the absence or presence of albumin; in comparison with control animals. We believe that these favorable effects may derive from ROS scavenging beneficial effects that preserve the GBM protein structure by reducing entactin and laminin degradation and type IV collagen cross-linking.

Vascular endothelial growth factor increases the ultrafiltration coefficient in isolated intact Wistar rat glomeruli

Vascular endothelial growth factor (VEGF) is expressed by the podocytes of renal glomeruli, and has profound influences on systemic microvascular permeability and haemodynamics. We describe an extensive refinement of a model that permits evaluation of the ultrafiltration coefficient (LpA) of isolated mammalian glomeruli, in the absence of circulating and haemodynamic influences, and tested the hypothesis that VEGF influences glomerular LpA via an effect on endothelial cells. Glomeruli were isolated by sieving Wistar rat renal cortical tissue, and individually loaded onto a suction micropipette. Flowing perifusate containing 1% bovine serum albumin (BSA) was rapidly switched to an oncopressive perifusate containing 8% BSA, eliciting transglomerular fluid efflux. The rate of the resultant reduction in glomerular volume was used to calculate glomerular LpA (1.07 +/- 0.53 nl min(-1) mmHg(-1) (mean +/-s.d.), n= 51), which compares favourably with those reported in the same rat strain using different techniques. A significant relationship between LpA and initial glomerular volume (Vi) (r= 0.72, n= 41, P < 0.0001) necessitated correction of LpA for Vi. The initial rate of change of glomerular volume, normalized for Vi, showed a strong positive correlation with applied oncotic gradient (Pearson r= 0.59, n= 28, P < 0.001), as predicted by Starling's law of filtration. A 60 min exposure of glomeruli to 1 nm VEGF increased glomerular LpA/Vi (1.19 +/- 0.19 (n= 10) to 2.23 +/- 0.33 (n= 9) min(-1) mmHg(-1) (mean +/-s.e.m.); P < 0.02). Time- and concentration-dependent relations between VEGF and LpA/Vi were observed. The VEGF-induced elevation of LpA/Vi was blocked by the selective VEGF-R2 inhibitor ZM323881. We suggest that glomerular VEGF contributes to the high physiological permeability of mammalian glomeruli to water through an action on endothelial cells.

Mycophenolate mofetil prevents arteriolopathy and renal injury in subtotal ablation despite persistent hypertension

BACKGROUND

Although renal protective effect of interrupting the inflammatory process is well established, it is still controversial if it also prevents the glomerular hemodynamic disturbances that initiate renal injury. We investigated the effects of suppressing inflammation with mycophenolate mofetil (MMF) on glomerular hemodynamics, arteriolar structural changes, and renal histologic injury in rats with subtotal renal ablation

METHODS

Micropuncture studies were performed 30 days after 5/6 nephrectomy in rats untreated and treated with MMF (30 mg/kg/day). Renal histology, immunohistochemistry for lymphocytes, macrophages and inducible nitric oxide synthase (iNOS) expression, as well as afferent arteriolar (AA) morphometry was evaluated.

RESULTS

Renal ablation significantly increased proteinuria (6.8 to 82.7 mg/day), mean arterial pressure (MAP) (120 to 166 mm Hg), single-nephron glomerular filtration rate (SNGFR) (34.8 to 56.3 nL/min), glomerular plasma flow (QA) (117.7 to 246.9 nL/min), and glomerular capillary pressure (PGC) (48.9 to 61.0 mm Hg). Afferent resistance (AR), efferent resistance, and ultrafiltration coefficient remained unchanged. Despite persisting arterial hypertension (152 mm Hg), MMF prevented proteinuria (13.3 mg/day), and significantly reduced SNGFR (44.4 nL/min), PGC (49.1 mm Hg), and QA (163.2 nL/min) due to a rise in AR (3.13 vs. 2.18 1010 dyn/sec/cm-5). Glomerular sclerosis, tubulointerstitial damage, lymphocyte and macrophage infiltration, and iNOS expression were significantly reduced by MMF, in addition hypertrophy of AA resistance evaluated by the media/lumen ratio was prevented (P < 0.001).

CONCLUSIONS

Reduction in proteinuria, SNGFR, QA, and PGC, despite elevated MAP, indicate preservation of AA function. These results suggest that inflammation associated arteriolopathy of AA contributes to glomerular hemodynamic disturbances that participate in the progression of renal disease.

N- and L-type calcium channel antagonist improves glomerular dynamics, reverses severe nephrosclerosis, and inhibits apoptosis and proliferation in an l-NAME/SHR model

OBJECTIVE

To determine the responses of the new dihydropyridine N- and L-type calcium antagonist, cilnidipine, on systemic and renal hemodynamics, glomerular dynamics, renal function, and histopathology in an Nomega-nitro-l-arginine methylester spontaneously hypertensive rat (l-NAME/SHR) model of nephrosclerosis.

METHODS

Five groups of 20-week-old male SHR were studied using renal micropuncture techniques and histopathological analyses: group 1, control; group 2, cilnidipine (10 mg/kg per day) by gavage, for 3 weeks; group 3, l-NAME (50 mg/l) in drinking water, for 3 weeks; group 4, combination of l-NAME and cilnidipine, for 3 weeks; group 5, l-NAME for 3 weeks, followed by cilnidipine for a subsequent 3 weeks.

RESULTS

Cilnidipine significantly reduced mean arterial pressure, total peripheral resistance and renal vascular resistance, while increasing effective renal blood flow and glomerular filtration rate (P < 0.01) in l-NAME/SHR. These hemodynamic changes were associated with significantly increased single nephron glomerular filtration rate (SNGFR) and plasma flow (SNPF) and decreased afferent glomerular arteriolar resistances when cilnidipine was used alone, and with increased SNGFR and SNPF, but decreased glomerular capillary pressure, afferent and efferent arteriolar resistances, urinary protein excretion, serum creatinine and uric acid concentrations (at least P < 0.05) in l-NAME-exacerbated SHR nephrosclerosis. In addition, glomerular and arteriolar injuries were markedly reversed (both P < 0.01), and glomerular apoptosis and cellular proliferation were inhibited and associated with glomerular tuft enlargement and an increase in cell number.

CONCLUSION

Cilnidipine not only prevented, but reversed, the severe renal hemodynamic and glomerular dynamic changes, including apoptosis and glomerular cellular proliferation, in l-NAME/SHR-exacerbated nephrosclerosis. This dual-channel calcium antagonist thus exerted renoprotective pathophysiological effects in the l-NAME/SHR.

Renal cortical vasoconstriction contributes to development of salt-sensitive hypertension after angiotensin II exposure

Rats that are administered angiotensin II (AngII) for 2 wk develop persistent salt-sensitive hypertension, which can be prevented by the immunosuppressor mycophenolate mofetil (MMF) given during the AngII infusion. This study examined the contribution of glomerular hemodynamics (GFR dynamics) in the post-AngII hypertensive response to a high-salt diet (HSD) and the effect of MMF treatment. During AngII administration, rats developed severe hypertension (systolic BP [SBP], 185 +/- 3.9 mmHg), proteinuria, afferent and efferent vasoconstriction, and glomerular hypertension. Rats that received AngII+MMF showed similar responses to AngII; however, they developed lower proteinuria (P < 0.05). At 2 wk, AngII was withdrawn and SBP returned toward normal. Rats were then placed on an HSD (4% NaCl), resulting in a progressive increase in SBP (155 +/- 8.2 mmHg at week 1 and 163 +/- 4.5 mmHg at week 5). GFR dynamic alterations persisted after AngII was stopped, i.e., afferent and efferent vasoconstriction, decreased glomerular plasma flow and single-nephron GFR, and lower ultrafiltration coefficient. These changes correlated with the thickening of the afferent arteriole and with focal tubulointerstitial injury. In the AngII+MMF group, SBP remained unchanged throughout the HSD period (146 +/- 2.3 mmHg at week 1 and 148 +/- 4.4 mmHg at week 5) in association with less afferent arteriolar thickening and tubulointerstitial injury. Single-nephron GFR, glomerular plasma flow, efferent resistance, and ultrafiltration coefficient returned to normal with a significant reduction in afferent resistance. These results suggest a critical role of cortical vasoconstriction in salt-sensitive hypertension. The MMF-induced prevention of these changes suggests that immune mechanisms are involved in the vasoconstrictive response.

Angiotensin type 1 receptor antagonism and ACE inhibition produce similar renoprotection in N(omega)-nitro-L>-arginine methyl ester/spontaneously hypertensive rats

This study was conducted to determine potentially differential effects between an angiotensin II type 1 (AT(1)) receptor antagonist and an ACE inhibitor on systemic, renal, and glomerular hemodynamics and pathological changes in spontaneously hypertensive rats (SHR) with N(omega)-nitro-L>-arginine methyl ester (L-NAME)-exacerbated nephrosclerosis. The hemodynamic, renal micropuncture, and pathological studies were performed in 9 groups of 17-week-old male SHR treated as follows: group 1, controls (n=16); group 2, candesartan (10 mg/kg per day for 3 weeks) (n=7); group 3, enalapril (30 mg/kg per day for 3 weeks) (n=8); group 4, candesartan (5 mg/kg per day) plus enalapril (15 mg/kg per day for 3 weeks) (n=9); group 5, L-NAME (50 mg/L in drinking water for 3 weeks) (n=17); group 6, L-NAME (50 mg/L) plus candesartan (10 mg/kg per day for 3 weeks) (n=7); group 7, L-NAME (50 mg/L) for 3 weeks followed by candesartan (10 mg/kg per day) for another 3 weeks (n=8); group 8, L-NAME (50 mg/L) plus enalapril (30 mg/kg per day for 3 weeks) (n=7); and group 9, L-NAME (50 mg/L) plus enalapril (30 mg/kg per day) and the bradykinin antagonist icatibant (500 microg/kg SC per day via osmotic minipump for 3 weeks) (n=7). Both candesartan and enalapril similarly reduced mean arterial pressure and total peripheral resistance index. These changes were associated with significant decreases in afferent and efferent glomerular arteriolar resistances as well as glomerular capillary pressure. Histopathologically, the glomerular and arterial injury scores were decreased significantly, and left ventricular and aortic masses also were diminished significantly in all treated groups. L-NAME-induced urinary protein excretion was prevented by both candesartan and enalapril. Thus, both AT(1) receptor and ACE inhibition prevented and reversed the pathophysiological alterations of L-NAME-exacerbated nephrosclerosis in SHR. Itatibant only blunted the antihypertensive effects of enalapril but did not attenuate the beneficial effects of ACE inhibition on the L-NAME-induced nephrosclerosis. Thus, the AT(1) receptor antagonism and ACE inhibition have similar renal preventive effects, which most likely were achieved through reduction in the effects of angiotensin II, and ACE inhibition of bradykinin degradation demonstrated little evidence of renoprotection.

Differential effects of T- and L-type calcium antagonists on glomerular dynamics in spontaneously hypertensive rats

To determine whether there is a difference in the effects of T- and L-type calcium antagonists on systemic, renal, and glomerular hemodynamics, the pathological changes of N(G)-nitro-L-arginine methyl ester (L-NAME)-exacerbated nephrosclerosis and clinical alterations were investigated in spontaneously hypertensive rats (SHR). Seven groups of 17-week-old male SHRs were studied: Group 1, control; Group 2, mibefradil, 50 mg. kg(-1). d(-1); Group 3, L-NAME in drinking water, 50 mg/L; Group 4, L-NAME (50 mg/L) plus mibefradil (50 mg. kg(-1). d(-1)); Group 5, L-NAME (50 mg/L) plus amlodipine (10 mg. kg(-1). d(-1)); Group 6 and 7, L-NAME (50 mg/L) for 3 weeks followed by mibefradil (50 mg. kg(-1). d(-1)) or amlodipine (10 mg. kg(-1). d(-1)), respectively, for the subsequent 3 weeks. Both the T- and L-channel calcium antagonists similarly reduced mean arterial pressure and total peripheral resistance index. These changes were associated with significant decreases in afferent and efferent glomerular arteriolar resistances and the ultrafiltration coefficient (P<0.01). Furthermore, the histopathological glomerular and arterial injury scores and urinary protein excretion were also significantly improved (P<0.01), and left ventricular and aortic masses were significantly diminished in all treated groups. Both drugs, mibefradil and amlodipine, had effects of increasing the single-nephron glomerular filtration ratio (SNGFR), and single-nephron plasma flow (SNPF), and of reducing glomerular afferent arteriolar resistance and urinary protein excretion. Thus, the T-type (mibefradil) and L-type (amlodipine) calcium antagonists each prevented and reversed the pathophysiological alterations of L-NAME-exacerbated hypertensive nephrosclerosis in SHR. The T-type calcium antagonist (mibefradil) seemed to have been more effective than the L-type amlodipine antagonist and it produced a greater reduction in afferent arteriolar resistance while preserving SNGFR.

The glomerular barrier fits a two-pore-and-fiber-matrix model: derivation and physiologic test

Failure of the glomerular barrier causing proteinuria has been modeled chiefly by Chang, Deen, and Brenner. They have refined models from an isoporous filter to a mostly isoporous membrane, which during proteinuric disease opens up nondiscriminating shunts. This report extends these concepts by measuring a larger distribution of macromolecular tracer sizes and bringing in a fiber matrix. By clearance methods, glomerular sieving curves of relatively neutral tetramethyl rhodamine aminodextran from radii of 15 to over 80 A were obtained and fitted to theory. Two pores filled with matrix fit all data without exception, and no other model did. Five parameters described the curve in control rats and in proteinuric rats made so by albumin injections. From highest to lowest degree of confidence, these were small and large pore radii ros = 42.7 +/- 0.9 SEM A and rol = 926 +/- 156 A; small to large pore density ns/nl = 3859 +/- 942; mean fiber radius rf = 20.3 +/- 1. 1 A; and fiber void volume ratio epsilon = 0.52 +/- 0.05. In proteinuria, ros rose 13% (P = 0.002), nl increased 150% (P = 0.04), and there was a compensatory rise in rf of 26% (P = 0.002). The consideration of basement membrane and glycocalyx remain to be incorporated into the model. Moreover, the closeness of rf to ros indicates that fiber matrix theory may need modification for a complete description.

Renoprotective effects of felodipine and/or enalapril in spontaneously hypertensive rats with and without L-NAME

To determine the renoprotective effects of a calcium antagonist (felodipine) and an angiotensin-converting enzyme (ACE) inhibitor (enalapril), alone or in combination, 10 groups of 19-week-old spontaneously hypertensive rats (SHR) (with or without N(G)-nitro-L-arginine methyl ester [L-NAME]) were studied using renal micropuncture techniques. Group 1 (control), group 2 (felodipine, 30 mg x kg(-1) x d[-1]), group 3 (enalapril, 30 mg x kg(-1) x d[-1]), and group 4 (felodipine plus enalapril, 15 mg x kg(-1) x d(-1) each agent) were studied after 3 weeks of treatment without L-NAME. L-NAME (50 mg/L) cotreatment was administered in drinking water to groups 6 through 10 using the same doses of each agent as in groups 1 through 4: group 5 (only L-NAME), group 6 (felodipine), group 7 (enalapril), and group 8 (felodipine plus enalapril). Groups 9 and 10 received L-NAME initially for 3 weeks followed by felodipine or felodipine plus enalapril, respectively, for the subsequent 3 weeks. All three treatments resulted in reductions in mean arterial pressure and total peripheral vascular resistance (P<.001) that were associated with important structural and functional renal microcirculatory improvements. Thus, the pathological nephrosclerosis (subcapsular and juxtamedullary) glomerular and arteriolar injury scores were improved (P<.05 at least) in association with normalization of afferent and efferent arteriolar resistances, and single-nephron glomerular filtration rate, plasma flow, and blood flow were significantly improved, as well as the ultrafiltration coefficient (compared with group 5, L-NAME). Thus, the calcium antagonist felodipine, alone or in combination with an ACE inhibitor, not only prevented but also reversed L-NAME-exacerbated hypertensive nephrosclerosis in SHR.

Renal vascular lesions in lupus nephritis

We retrospectively studied the prevalence, histologic features, clinical correlations, and long-term outcome of the intrarenal vascular lesions of lupus nephritis (LN) in a series of 169 renal biopsies performed between 1980 and 1994 in 132 patients with systemic lupus erythematosus. The most common vascular lesions were nonspecific sclerotic changes, found in 37% of the biopsies (24% if only the cases with moderate to severe changes are considered). The other common vascular lesions were "immunoglobulin microvascular casts," found in 24% of the biopsies. Vasculitis and thrombotic microangiopathy were rare lesions and were seen in only 4 (2.4%) and 1 (0.6%) cases, respectively. Isolated sclerotic vascular changes were present in biopsies from older patients with a longer duration of LN, compared with the group with no vascular lesions, and were associated with a significantly higher prevalence of hypertension. Overall, however, the long-term renal and patient survival of this group did not differ significantly from that of the patients without vascular changes. Immunoglobulin microvascular casts (IMCs) ("lupus vasculopathy") were characterized by the presence of immunoglobulin deposition within the glomerular capillaries and small arterioles. In the present study we extensively investigated the morphologic and immunologic features of this lesion. The lesions were notable for the absence of endothelial or parietal vascular lesions and of fibrin, platelets, and leukocytes, which indicates that thrombosis is not involved in the vascular obstruction. According to our data immunoglobulin precipitation in the microvasculature seems to play a central role in the pathogenesis of this lesion, which is why we propose the term "immunoglobulin microvascular casts." In general, IMCs were associated with the most severe and active forms of diffuse proliferative lupus nephritis (World Health Organization [WHO] class IV). However our data show that, in contrast to previous studies, the long-term outcome of patients with IMCs is not worse than that of other patients with class IV LN. It may even be somewhat better, suggesting that this type of lesion may reverse with immunosuppressive therapy. In addition, we did not find any association between the presence of IMCs and the lupus anticoagulant, IgG anticardiolipin antibodies, or extrarenal vascular manifestations. Concerning vasculitis and thrombotic microangiopathy, our results confirm that their occurrence is quite rare in-lupus nephritis. The outcome of our 4 patients with vasculitis was not particularly poor, which could be related to early and/or aggressive treatment. Taken as a whole, our data confirm that the presence of active and severe forms of diffuse proliferative LN (WHO class IV) carries a worse prognosis compared with the other forms of LN. In our study, and in agreement with previous reports (23), the long-term renal survival of patients with class IV LN was significantly worse than that of patients with other forms of LN, with a 10-year renal survival of 70% compared with 85%, respectively. However our data do not support the conclusions of some previous studies that the presence of intrarenal vascular lesions is a marker of poor renal prognosis in lupus nephritis. More precisely, our data show that the somewhat poorer renal outcome observed in patients with IMCs is related to the fact that in most cases these lesions are associated with class IV lupus nephritis, and not related to the presence of the vascular lesion per se.

Effects of long-term training on the progression of chronic renal failure in rats

To evaluate the effects of long-term exercise on the progression of chronic renal failure (CRF), adult Munich-Wistar rats with 5/6 renal mass ablation were submitted to treadmill exercise for 30 min 5 times/wk for 60 d. Whole kidney function and glomerular hemodynamics, proteinuria, and glomerular sclerosis were evaluated in 4 groups: Control, Sham trained (Sham + Ex), rats submitted to 5/6 nephrectomy (CRF) and maintained sedentary, and rats with 5/6 nephrectomy and trained (CRF + Ex). The groups with chronic renal failure (sedentary and trained) presented a reduction in total glomerular filtration rate (GFR) and in renal plasma flow (RPF), accompanied by an increase in single nephron GFR (SNGFR) and glomerular plasma flow (QA). However, the CRF + EX group did not show the glomerular hypertension observed in the CRF group. Despite the normalization of glomerular hypertension, proteinuria and sclerosis index were not different from the CRF sedentary group. Physical training provoked a vasodilatation of efferent arterioles, which induced the normalization of glomerular hypertension. These results suggest that the reduction alone of glomerular hypertension induced by exercise does not prevent the progression of renal disease, indicating the participation of other associated factors in this experimental model.

Hydrochlorothiazide Increases Efferent Glomerular Arteriolar Resistance in Spontaneously Hypertensive Rats

BACKGROUND: Micropuncture studies were performed to determine the intrarenal hemodynamic effects of two conventional antihypertensive agents, hydrochlorothiazide (HCTZ) and hydralazine (HYDR) alone and in combination. METHODS AND RESULTS: Male spontaneously hypertensive and normotensive Wistar Kyoto rats (19 weeks old) were treated for 3 weeks with vehicle (control), HCTZ (80 mg/kg/d), HYDR (5 mg/kg/d), or combined therapy (HCTZ 30 mg/kg/d and HYDR 2 mg/kg/d). Each treatment significantly reduced arterial pressure while effective renal plasma flow, glomerular filtration rate and single nephron glomerular filtration rate were unaffected by any treatment in either strain. In spontaneously hypertensive rats HCTZ decreased single nephron plasma flow (111 +/- 8 to 84 +/- 4 nL/min; P <.05) but, despite this reduction, glomerular pressure remained unchanged (51.4 +/- 0.7 to 52.1 +/- 0.8 mmHg) attributable to increased efferent glomerular resistance (1.58 +/- 0.14 to 2.11 +/- 0.12 10 U; P <.05). By contrast, HYDR increased single nephron plasma flow (to 147 +/- 8 nL/min; P <.01) and decreased efferent glomerular resistance (to 1.09 +/- 0.09 U; P <.05). Combined treatment produced responses similar to HCTZ when used alone, thereby nullifying the beneficial efferent glomerular resistance effects: single nephron plasma flow +/- fell (to 89 +/- 7 nL/min; P <.05) and efferent glomerular resistance increased (to 2.05 +/- 0.17 U; P <.05). In Wistar Kyoto rats, HCTZ and combined treatment had no effect. HCTZ alone induced glomerular ischemia that was associated with efferent glomerular arteriolar constriction in these spontaneously hypertensive rats. CONCLUSIONS: These findings provide a possible explanation for the lack of improved renal target-organ damage in controlled multicenter trials employing thiazide diuretics.

Nitric oxide synthase inhibition in spontaneously hypertensive rats. Systemic, renal, and glomerular hemodynamics

To investigate the prolonged effects of nitric oxide inhibition on systemic, renal, and glomerular hemodynamics, the effects of the nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) on cardiac index, renal micropuncture results, urinary excretion, and histology were obtained in 20-week-old male spontaneously hypertensive rats (SHR) that were divided into two groups: untreated and L-NAME-treated (50 mg/L), each followed for 3 weeks. Cardiac index and effective renal plasma flow decreased (P < .01) in L-NAME-treated SHR, exhibiting a positive correlation (r = .816; P < .0001). Single-nephron plasma flow (123 +/- 8 versus 80 +/- 12 nL/min per gram; P < .01) and ultrafiltration coefficient (P < .05) were also reduced in L-NAME-treated SHR versus controls. Most notably, the L-NAME-treated SHR had increased afferent (4.4 +/- 0.3 versus 9.5 +/- 1.3 U; P < .01) and efferent (1.4 +/- 0.1 versus 2.7 +/- 0.3 U; P < .01) glomerular arteriolar resistances versus controls. These functional changes were associated with significantly altered afferent arteriolar (P < .001) and glomerular (P < .005) histological injury scores accompanied by marked proteinuria (P < .001). Because of the intense afferent glomerular artery constriction and lesser increase in efferent glomerular arteriolar resistance associated with reduced single-nephron plasma flow, glomerular capillary pressure did not increase in the L-NAME-treated SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

FK 506: effects on glomerular hemodynamics and on mesangial cells in culture

FK 506 is a new immunosuppressive drug that, like cyclosporine A (CsA), presents nephrotoxicity. Glomerular hemodynamic studies showed that acute FK 506 infusion (N = 9, 3 mg/kg body wt, i.v. in bolus) caused a 57% reduction in glomerular filtration rate (GFR) (0.74 +/- 0.03 to 0.32 +/- 0.02 ml/min, P < 0.05) and a 40% reduction in single nephron glomerular filtration rate (SNGFR; 43.0 +/- 5.2 to 26.0 +/- 2.5 nl/min, P < 0.05) due to a 25% reduction in glomerular plasma flow rate (QA) (133.4 +/- 19.8 to 99.8 +/- 12.0 nl/min) and a 22% reduction in glomerular ultrafiltration coefficient (Kf; 0.1009 +/- 0.0203 to 0.0790 +/- 0.0130 nl/sec. mm Hg). After 10 days of FK treatment (N = 8, 0.6 mg/kg body wt, i.p.), we observed a reduction of 23% in GFR (0.97 +/- 0.02 to 0.75 +/- 0.04 ml/min, P < 0.05) and of 23% in SNGFR (37.9 +/- 3.0 to 29.1 +/- 1.9 nl/min, P < 0.05) due to a 42% reduction in Kf (0.1486 +/- 0.0101 to 0.0870 +/- 0.0110 nl/sec.mm Hg, P < 0.05) and a 38% reduction in QA (117.6 +/- 10.2 to 73.5 +/- 6.1 nl/min, P < 0.05). The latter was consequent to the increment of 72% in total arteriolar resistance (RT) (3.1 +/- 0.2 to 5.2 +/- 0.5 +/- 0.5 10(10).dyn.sec.cm-5, P < 0.05). Thus, the pattern of FK 506 effect on glomerular hemodynamics was similar in both acute and chronic treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Glomerular dynamics and morphology of aged spontaneously hypertensive rats. Effects of angiotensin-converting enzyme inhibition

Relationships between glomerular dynamics and renal injury, micropuncture and histological studies were assessed in 73 week-old normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats divided into untreated and angiotension-converting enzyme inhibitor-treated (quinapril; 3 mg/kg/day; for 3 weeks) groups. Urinary protein excretion (UPE) and histologic arteriolar (AIS) and glomerular (GIS) injury scores were determined. Mean arterial pressure (MAP) of untreated SHR was increased compared with WKY (200 +/- 6 vs 119 +/- 4 mm Hg; P < 0.01), effective renal plasma flow (ERPF) was reduced (1.47 +/- 0.21 vs 3.06 +/- 0.26 ml/min/per g; P > 0.01), and filtration fraction (FF) and total renal vascular resistance (RVR) of SHR were increased (P < 0.01). Single-nephron plasma flow (SNPF) of untreated SHR was decreased (174 +/- 17 vs 80 +/- 9 ml/min; P < 0.01), and single-nephron filtration fraction and afferent arteriolar resistance (RA) were increased (19.4 +/- 1.8 vs 30.0 +/- 2.5% and 1.90 +/- 0.25 vs 9.05 +/- 1.35 U, respectively; both P < 0.01). Despite reduced SNPF, glomerular capillary pressure (PG) increased (49.7 +/- 0.7 vs 53.8 +/- 1.3 mm Hg; P < 0.05), the result of efferent arteriolar constriction (1.15 +/- 0.18 vs 2.84 +/- 0.36 U; P < 0.01). Untreated SHR had higher UPE (13.9 +/- 1.5 vs 42.8 +/- 3.2; mg/100 g per day; P < 0.01) and GIS and AIS scores than WKY (4.3 +/- 1.1 vs 64.3 +/- 8.4 and 16.6 +/- 3.1 vs 96.3 +/- 14.4; both P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary fatty acids and the glomerular hemodynamic response to cyclosporine in borderline hypertensive rats

We have recently reported that cyclosporine A (CsA) decreases glomerular filtration rate in the borderline hypertensive rat (BHR), but that the glomerular filtration rate is normal when the rats are maintained on a diet supplemented with evening primrose (EP) oil. The current studies were designed to determine the glomerular hemodynamic changes responsible for this effect. A first group (PLAC-SAFF) received a diet supplemented with safflower oil (SAFF) (10% of calories) and placebo (PLAC). A second group (CsA-SAFF) received a diet supplemented with SAFF and CsA (10 mg/kg/day). A third group (CsA-EP) also received CsA, but the diet was supplemented with EP oil (10% of calories). Routine micropuncture studies were performed after five to nine weeks of treatment. Single nephron glomerular filtration rate (SNGFR) was lower in CsA-SAFF than in PLAC-SAFF (36 +/- 2 vs. 46 +/- 1 nl/min, p < 0.05). Maintenance of SNGFR in CsA-EP compared to CsA-SAFF (48 +/- 2 nl/min vs. 36 +/- 2 nl/min, P < 0.05) was due to higher values for single nephron plasma flow rate (156 +/- 16 vs. 118 +/- 9off/min, P < 0.05), and higher values for the glomerular capillary ultrafiltration coefficient (0.091 +/- 0.013 vs. 0.054 +/- 0.010 nl/s/mm Hg, P < 0.05). Since dietary fatty acids can affect prostaglandin (PG) production, we measured PGE production in isolated glomeruli. Mean values for basal production rates of PGE were greater in rats maintained on EP than in rats maintained on SAFF (3958 +/- 105 vs. 3378 +/- 146 pg PGE/mg glomerular protein, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Renal function and hemodynamic study in obese Zucker rats

OBJECTIVES

To investigate the renal function and hemodynamic changes in obesity and hyperinsulinemia which are characteristics of type II diabetes.

METHODS

Studies were carried out in two groups of female Zucker rats. Group 1 rats were obese Zucker rats with hereditary insulin resistance. Group 2 rats were lean Zucker rats and served as controls. In comparison with lean Zucker rats, obese Zucker rats exhibited hyperinsulinemia but normoglycemia. Micropuncture studies and morphologic studies were performed in these rats.

RESULTS

Functional studies showed that obese Zucker rats exhibited increases in kidney weight and GFR(obese Zucker, 1.23 +/- .07)ml/min; lean Zucker, 0.93 +/- .03ml/min). Micropuncture studies revealed that the increase in GFR in obese Zucker rats was attributable to the increases in the single nephron plasma flow rate and glomerular transcapillary hydraulic pressure. The glomerular ultrafiltration coefficient was the same in both groups. Morphologic studies revealed that the increase in GFR in obese Zucker rats was associated with an increase in glomerular volume.

CONCLUSIONS

These results suggest that obesity and hyperinsulinemia, which are the characteristics of type II diabetes, can be associated with glomerular hyperfiltration and glomerular capillary hypertension.

Intrarenal hemodynamics in low- and high-output cardiac failure in rats

Cardiac failure is multifactorial in causation, and the underlying physiologic mechanisms are variable, yet their renal effects have been considered more homogeneous. To investigate and compare the intrarenal hemodynamic characteristics in two experimental types (low- and high-output) of cardiac failure, renal micropuncture studies were performed in rats after myocardial infarction (MI) and arteriovenous fistula, respectively. Myocardial infarction was produced by ligation of the left main coronary artery and arteriovenous fistula by direct puncture of the aorta and inferior vena cava below the renal arteries. Pressures and interrenal and glomerular dynamics were obtained using classic micropuncture techniques. Both forms of cardiac failure were characterized by elevated left ventricular end-diastolic pressure (LVEDP), reduced mean arterial pressure, and increased cardiac mass. Left ventricular end-diastolic pressure was higher in MI rats, and effective renal plasma flow (ERPF) tended to be reduced in both forms of cardiac failure. There were no apparent differences in effective renal plasma flow between two models. In addition, single-nephron plasma flow and single-nephron glomerular filtration rate were reduced, and single-nephron filtration fraction and glomerular capillary pressure (PG) were increased in both models. These changes were associated with higher afferent and efferent arteriolar resistances and lower ultrafiltration coefficients. Despite these similarities, PG was higher in MI rats, yet LVEDP correlated directly with PG (r = 0.73; P < 0.001) and efferent arteriolar resistances (r = 0.72; P < 0.01). Therefore, although systemic arterial pressure and effective renal plasma flow were similar in both models of cardiac failure, PG was significantly higher in MI rats with higher LVEDP than in arteriovenous fistula rats.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Modulation of glomerular hypertension defines susceptibility to progressive glomerular injury

The fawn-hooded rat constitutes a spontaneous model for chronic renal failure with early systemic and glomerular hypertension, proteinuria (UpV) and high susceptibility to development of focal and segmental glomerular sclerosis (FGS). It has been argued that uninephrectomy (UNX) accelerates the development of glomerular injury by aggravation of glomerular hypertension and by an independent effect to promote glomerular enlargement. The present study was performed to further delineate the importance of these parameters for the development of FGS. At the age of eight weeks male rats were UNX and randomly assigned to either control (CON), enalapril (ENA) or Nw-nitro L-arginine methyl ester (NAME) treatment. In all groups glomerular hemodynamic studies were performed four weeks post-UNX. Systemic blood pressure and UpV were monitored for 4 to 12 weeks post-UNX. Kidneys were then prepared for morphologic study. ENA treatment achieved control of both systemic and glomerular hypertension, maintenance of glomerular hyperfiltration and hyperperfusion, increased ultrafiltration coefficient(Kf), and long-term protection against UpV and FGS. NAME rats showed aggravation of both systemic and glomerular hypertension, decreased renal perfusion and filtration with reduced Kf, and high filtration fraction. The incidence of FGS in NAME and CON groups was similar at 8 and 12 weeks post-UNX, respectively. Glomerular enlargement was present in CON and ENA rats, but did not correlate with injury, while glomerular tuft size was lowest in NAME rats, which displayed prominent glomerular injury. Systemic blood pressure correlated strongly with glomerular capillary pressure. We conclude that systemic and glomerular hypertension govern the development of UpV and FGS.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute, subacute, and chronic x-ray effects on glomerular hemodynamics in rats

In order to evaluate the effects of x-rays on glomerular hemodynamics, surgically exposed left kidneys of Munich-Wistar rats were irradiated with 15 Gy in a single dose. The animals were studied 45 min (acute group, n = 8), 14 days (subacute group, n = 7), and 60 days (chronic group, n = 7) after irradiation and compared with their respective controls. A decrease in total glomerular filtration (55%) and renal plasma flow (40%) rates with marked elevation of total renal vascular resistance (180%), p < 0.05, occurred within 45 min. Significant changes also occurred in the microcirculation; i.e., single-nephron glomerular filtration (SNGFR), glomerular plasma flow (QA), and glomerular capillary hydraulic pressure (PGC) declined by 35%, 40%, and 12%, respectively, due to an increase in total arteriolar resistance (90%), p < 0.05. Within 14 days, SNGFR was similar to control in spite of a moderate elevation of afferent arteriolar resistance (26%) and reduction in PGC (11%), p < 0.05, and QA (20%). Kf was significantly elevated (46%), p < 0.05. The chronic group presented a response pattern similar to that of the acute group, although less severe. Histopathological changes were not relevant and were restricted to tubules. The present results suggest that: (a) Acutely, there was a marked reduction in filtration, flow, and PGC with significant elevation of resistances. (b) Within 14 days, the maintenance of SNGFR was probably the result of an offsetting effect between QA and PGC decreases and Kf elevation. (c) After 60 days, the homeostatic mechanism was not sufficient to maintain normal renal function. (d) A functional effect is probably the most important pathogenetic mechanism, at least during the initial phase, for the development of radiation nephropathy since no morphological alterations were observed.

Bradykinin causes selective efferent arteriolar dilation during angiotensin I converting enzyme inhibition

We studied the effects of interruption of the renin-angiotensin system (RAS) in rats that were volume depleted by water deprivation for 48 hours (AWD) with/without furosemide (AWD + F), a condition known to activate RAS. Following baseline micropuncture, AWD rats (N = 6) were treated with a specific angiotensin II type 1 receptor antagonist (AIIRA; 4 mg/kg body wt bolus i.v. and then continuous infusion) and glomerular hemodynamics compared to those obtained during angiotensin I converting enzyme inhibitor treatment (ACEI; 24 mg/kg bolus i.v. and then continuous infusion). Systemic blood pressure decreased equally following AIIRA and ACEI. Single nephron glomerular filtration rate (SNGFR) increased from baseline following AIIRA (24 nl/min vs. 30, P < 0.025). While a decrease in efferent arteriolar resistance (RE) reduced glomerular capillary pressure (PGC; 67 mm Hg vs. 60, P < 0.05), this change in RE together with decrease in afferent arteriolar resistance (RA), enhanced glomerular plasma flow rate (QA; 80 nl/min vs. 111). Antagonizing angiotensin II receptor increased QA which, together with the tendency to increase glomerular capillary ultrafiltration coefficient, Kf, served to improve glomerular filtration. By contrast, although inhibition of the angiotensin I converting enzyme caused greater vasodilatation, no increase in SNGFR occurred. The lack of response in filtration after ACEI was due to a further fall in PGC to 52 mm Hg (P < 0.01 vs. AIIRA), reflecting profound reduction in RE. Since ACEI but not AIIRA potentiates bradykinin activity we examined effects of a specific bradykinin antagonist (Hoe).(ABSTRACT TRUNCATED AT 250 WORDS)

Glomerular permeability barrier in the rat. Functional assessment by in vitro methods

The formation of glomerular ultrafiltrate is dependent on the prevailing hemodynamic forces within the glomerular microcirculation and the intrinsic properties of the filtration barrier. However, direct assessment of the permeability barrier is difficult with most available techniques. We used confocal microscopy to image 1-micron thick optical cross-sections of isolated intact glomeruli and glomeruli denuded of cells and quantitated dextran (70,000 mol wt) diffusion from the capillary lumen. Dextran permeance was 11 times greater for the acellular filtration barrier than the intact peripheral capillary. Consideration of the basement membrane and cells as series resistors demonstrated that cells of the filtration barrier contribute 90% of the total resistance to macromolecular permeance. Using a different approach, dextran sieving coefficients for acellular glomeruli consolidated as a multilayer sheet in a filtration cell were similar to those for intact glomeruli in vivo at radii 30-36 A and approximately 50 times greater at a dextran radius of 60 A. The presence of cells significantly reduced hydraulic permeability determined on consolidated intact or acellular glomeruli in an ultrafiltration cell with 50 mmHg applied pressure. The glomerular basement membrane does restrict macromolecular permeability but cells are important determinants of the overall macromolecular and hydraulic permeability of the glomerulus.

Leukotriene D4 is a mediator of proteinuria and glomerular hemodynamic abnormalities in passive Heymann nephritis

We assessed the role of leukotrienes (LTs) in Munich-Wistar rats with passive Heymann nephritis (PHN), an animal model of human membranous nephropathy. 10 d after injection of anti-Fx1A antibody, urinary protein excretion rate (Upr) in PHN was significantly higher than that of control. Micropuncture studies demonstrated reduced single nephron plasma flow and glomerular filtration rates, increased transcapillary hydraulic pressure difference, pre- and postglomerular resistances, and decreased ultrafiltration coefficient in PHN rats. Glomerular LTB4 generation from PHN rats was increased. Administration of the 5-LO activating protein inhibitor MK886 for 10 d markedly blunted proteinuria and normalized glomerular hemodynamic abnormalities in PHN rats. An LTD4 receptor antagonist SK&F 104353 led to an immediate reduction in Upr and to reversal of glomerular hemodynamic impairment. Ia(+) cells/glomerulus were increased in PHN rats. In x-irradiated PHN rats, which developed glomerular macrophage depletion, augmented glomerular LT synthesis was abolished. Thus, in the autologous phase of PHN, LTD4 mediates glomerular hemodynamic abnormalities and a hemodynamic component of the accompanying proteinuria. The synthesis of LTD4 likely occurs directly from macrophages or from macrophage-derived LTA4, through LTC4 synthase in glomerular cells.

Studies on the glomerular microcirculatory actions of manidipine and its modulation of the systemic and renal effects of endothelin

We examined the actions of intravenously administered manidipine on systemic and renal microcirculatory hemodynamics and its efficacy in antagonizing endothelin-1 (ET-1)-evoked responses. Manidipine was a potent vasodilator with preferential activity in the renal vasculature. Its administration in optimal doses resulted in decreases in systemic arterial pressures accompanied by increases in renal perfusion and filtration rates. Its primary sites of action in the kidney were at both pre- and postglomerular arteriolar sites. Manidipine was capable of near-total reversal of the sustained elevations in arterial pressure and the progressive reductions in renal blood flow and glomerular filtration rates induced by intravenously administered ET-1. In the presence of prolonged calcium channel blockade, subsequent administration of ET-1 led to paradoxic hypotensive responses, which could be profound and blocked by an inhibitor of nitric oxide synthesis. These unexpected vasorelaxant actions of ET-1 in the presence of manidipine were likely caused by the dual effects of antagonism of its own intrinsic vasoconstrictor action (through calcium channel blockade), as well as ET-1-evoked release of the endothelium-derived relaxing factor, nitric oxide.

Effects of angiotensin II receptor blockade on remnant glomerular permselectivity

This study examined the mechanisms by which angiotensin II (Ang II) receptor blockade improves glomerular barrier function in rats with reduced nephron number. Proteinuria was measured at four weeks after 5/6 renal ablation, and rats were then divided into a group which received the Ang II receptor blocker MK954 and a group which received no treatment. Studies performed one week later showed that Ang II receptor blockade reduced proteinuria without altering GFR in renal ablated rats. Micropuncture studies showed that Ang II blockade reduced both mean arterial pressure (142 +/- 7 mm Hg, ablation without treatment; 105 +/- 2 mm Hg, ablation with treatment) and glomerular transcapillary pressure (54 +/- 3 mm Hg, ablation without treatment; 43 +/- 1 mm Hg, ablation with treatment). Dextran sieving studies showed that untreated rats developed a size-selective defect characterized by increased transglomerular passage of neutral dextrans with radii 54 to 76 A and a charge-selective defect characterized by an increased transglomerular passage of anionic dextran sulfate with a radius of approximately 18 A. Ang II blockade reduced fractional clearance values for large neutral dextrans near to values observed in normal rats but had no effect on the fractional clearance of dextran sulfate (0.68 +/- 0.11, ablation without treatment; 0.66 +/- 0.08, ablation with treatment; 0.46 +/- 0.05, normal rats). These findings indicate that reducing Ang II activity improves size-selectivity without affecting charge-selectivity in injured remnant glomeruli.

Angiotensin II receptor blockade limits glomerular injury in rats with reduced renal mass

The effects of angiotensin II (AII) blockade were compared with the effects of angiotensin converting enzyme inhibition in rats with reduced nephron number. Rats were subjected to five-sixths renal ablation and divided into four groups with similar values for blood pressure and serum creatinine after 2 wk. Group 1 then served as untreated controls, while group 2 received the AII receptor antagonist MK954 (which has previously been designated DuP753), group 3 received the converting enzyme inhibitor enalapril, and group 4 received a combination of reserpine, hydralazine, and hydrochlorothiazide. Micropuncture and morphologic studies were performed 10 wk later. Converting enzyme inhibition, AII receptor blockade, and the combination regimen were equally effective in reversing systemic hypertension (time-averaged systolic blood pressure: group 1, 185 +/- 5 mmHg; group 2, 125 +/- 2 mmHg; group 3, 127 +/- 2 mmHg; group 4, 117 +/- 4 mmHg). Micropuncture studies showed that glomerular transcapillary pressure was reduced significantly by converting enzyme inhibition and by AII blockade but not by the combination regimen (delta P: group 1, 49 +/- 1 mmHg; group 2, 42 +/- 1 mmHg; group 3, 40 +/- 2 mmHg, group 4, 47 +/- 1 mmHg). Reduction of systemic blood pressure was associated with the development of markedly less proteinuria and segmental glomerular sclerosis in rats receiving enalapril and MK954 but not in rats receiving the combination regimen (prevalence of glomerular sclerotic lesions: group 1, 41 +/- 4%; group 2, 9 +/- 1%; group 3, 9 +/- 1%; group 4, 33 +/- 6%). These results indicate that the effects of converting enzyme inhibition on remnant glomerular function and structure depend on reduction in AII activity and are not attributable simply to normalization of systemic blood pressure.

Glomerular actions of a free radical-generated novel prostaglandin, 8-epi-prostaglandin F2 alpha, in the rat. Evidence for interaction with thromboxane A2 receptors

8-epi-prostaglandin F2 alpha (8-epi-PGF2 alpha) and related compounds are novel prostanoid produced by a noncyclooxygenase mechanism involving lipid peroxidation. Renal ischemia-reperfusion injury increased urinary excretion of these compounds by 300% over baseline level. Intrarenal arterial infusion at 0.5, 1, and 2 micrograms/kg per min induced dose-dependent reductions in glomerular filtration rate (GFR) and renal plasma flow, with renal function ceasing at the highest dose. Micropuncture measurements (0.5 microgram/kg per min) revealed a predominant increase in afferent resistance, resulting in a decrease in transcapillary hydraulic pressure difference, and leading to reductions in single nephron GFR and plasma flow. These changes were completely abolished or reversed by a TxA2 receptor antagonist, SQ 29,548. Competitive radioligand binding studies demonstrated that 8-epi-PGF2 alpha is a potent competitor for [3H]SQ 29,548 binding to rat renal arterial smooth muscle cells (RASM) in culture. Furthermore, addition of 8-epi-PGF2 alpha to RASM or isolated glomeruli was not associated with stimulation of arachidonate cyclooxygenase products. Therefore, 8-epi-PGF2 alpha is a potent preglomerular vasoconstrictor acting principally through TxA2 receptor activation. These findings may explain, in part, the beneficial effects of antioxidant therapy and TxA2 antagonism observed in numerous models of renal injury induced by lipid peroxidation.

Essential fatty acid deficiency normalizes function and histology in rat nephrotoxic nephritis

The central lipid abnormality in essential fatty acid deficiency (EFAD) is the lack of availability of arachidonic acid. To examine the role of total eicosanoid's biosyntheses in the pathology and pathophysiology of glomerulonephritis, EFAD was induced in weanling rats, which were then subjected to antiglomerular basement membrane antibody (NTS)-induced injury in adulthood. Glomerular dynamics (as assessed by micropuncture), quantitative histology, and eicosanoid generation rates were measured at two hours and two weeks post-NTS, and compared to those of standard diet-fed (STD) controls. Two hours post-NTS, and despite the occurrence of proteinuria in both EFAD and STD animals, glomerular dynamics were essentially normal in EFAD rats, whereas STD animals had reduced values for glomerular filtration rate (GFR) and renal plasma flow rate (RPF). At two weeks, severe histologic changes were observed in STD animals including mesangial and stalk hypercellularity, moderate sclerosis, and interstitial nephritis, coupled with heavy proteinuria and reduced GFR and RPF. In dramatic contrast, EFAD rats displayed totally normal glomerular structures and functions. In parallel, glomerular generation rates of prostaglandin E2 and thromboxane A2 were suppressed markedly in EFAD rats. Thus, EFAD confers complete protection against the histopathologic and functional sequelae of immune-initiated injury in the glomerulus. The data suggest that the initial wave of complement-induced neutrophil infiltration (with resultant proteinuria) is not sufficient to perpetuate injury into the more destructive chronic phases. The results provide strong impetus for the design of more specific interventional therapies targeting the various enzymes and products of arachidonic acid metabolism in the attempts to control glomerular inflammation.

Nifedipine versus fosinopril in uninephrectomized diabetic rats

Antihypertensive agents have been shown to exert inequivalent effects on glomerular injury in experimental renal disease models. To compare the consequences of dissimilar antihypertensive regimens on the development of diabetic glomerulopathy, studies were performed in three groups of uninephrectomized moderately hyperglycemic diabetic rats. One group (DM) received no therapy except insulin. The remaining groups received insulin and either the angiotensin I converting enzyme inhibitor, fosinopril (FOS), or the calcium channel blocker, nifedipine (NIF). Both drugs lowered blood pressure comparably. At four to eight weeks, DM rats exhibited elevation of the single nephron glomerular filtration rate (SNGFR), due to elevations of the glomerular capillary plasma flow rate (QA) and the glomerular capillary hydraulic pressure (PGC). Neither NIF nor FOS affected values for SNGFR or QA. However, while FOS lowered PGC and increased Kf, NIF did not affect these parameters. In longer term (8 month) studies, DM rats exhibited progressive albuminuria and glomerular sclerosis. FOS markedly limited development of albuminuria and glomerular injury, but NIF was ineffective in limiting either parameter of glomerular injury. Thus, in contrast to the beneficial effects of converting enzyme inhibitors, chronic calcium channel blockade with nifedipine fails to limit PGC or glomerular injury in diabetic rats. These findings lend further support to the concept that different classes of antihypertensive agents are not equally effective in protecting against diabetic glomerulopathy.