Relation of glomerular injury to preglomerular resistance in experimental hypertension

Upregulation of Piezo2 in the mesangial, renin, and perivascular mesenchymal cells of the kidney of Dahl salt-sensitive hypertensive rats and its reversal by esaxerenone

The recent discovery of mechanosensitive ion channels has promoted mechanobiological research in the field of hypertension and nephrology. We previously reported Piezo2 expression in mouse mesangial and juxtaglomerular renin-producing cells, and its modulation by dehydration. This study aimed to investigate how Piezo2 expression is altered in hypertensive nephropathy. The effects of the nonsteroidal mineralocorticoid receptor blocker, esaxerenone, were also analyzed. Four-week-old Dahl salt-sensitive rats were randomly assigned to three groups: rats fed a 0.3% NaCl diet (DSN), rats fed a high 8% NaCl diet (DSH), and rats fed a high salt diet supplemented with esaxerenone (DSH + E). After six weeks, DSH rats developed hypertension, albuminuria, glomerular and vascular injuries, and perivascular fibrosis. Esaxerenone effectively decreased blood pressure and ameliorated renal damage. In DSN rats, Piezo2 was expressed in Pdgfrb-positive mesangial and Ren1-positive cells. Piezo2 expression in these cells was enhanced in DSH rats. Moreover, Piezo2-positive cells accumulated in the adventitial layer of intrarenal small arteries and arterioles in DSH rats. These cells were positive for Pdgfrb, Col1a1, and Col3a1, but negative for Acta2 (αSMA), indicating that they were perivascular mesenchymal cells different from myofibroblasts. Piezo2 upregulation was reversed by esaxerenone treatment. Furthermore, Piezo2 inhibition by siRNA in the cultured mesangial cells resulted in upregulation of Tgfb1 expression. Cyclic stretch also upregulated Tgfb1 in both transfections of control siRNA and Piezo2 siRNA. Our findings suggest that Piezo2 may have a contributory role in modulating the pathogenesis of hypertensive nephrosclerosis and have also highlighted the therapeutic effects of esaxerenone on salt-induced hypertensive nephropathy. Mechanochannel Piezo2 is known to be expressed in the mouse mesangial cells and juxtaglomerular renin-producing cells, and this was confirmed in normotensive Dahl-S rats. In salt-induced hypertensive Dahl-S rats, Piezo2 upregulation was observed in the mesangial cells, renin cells, and notably, perivascular mesenchymal cells, suggesting its involvement in kidney fibrosis.

Comparative analysis of hypertensive nephrosclerosis in animal models of hypertension and its relevance to human pathology. Glomerulopathy

Current research on hypertension utilizes more than fifty animal models that rely mainly on stable increases in systolic blood pressure. In experimental hypertension, grading or scoring of glomerulopathy in the majority of studies is based on a wide range of opinion-based histological changes that do not necessarily comply with lesional descriptors for glomerular injury that are well-established in clinical pathology. Here, we provide a critical appraisal of experimental hypertensive glomerulopathy with the same approach used to assess hypertensive glomerulopathy in humans. Four hypertensive models with varying pathogenesis were analyzed–chronic angiotensin II infused mice, mice expressing active human renin in the liver (TTRhRen), spontaneously hypertensive rats (SHR), and Goldblatt two-kidney one-clip rats (2K1C). Analysis of glomerulopathy utilized the same criteria applied in humans–hyalinosis, focal segmental glomerulosclerosis (FSGS), ischemic, hypertrophic and solidified glomeruli, or global glomerulosclerosis (GGS). Data from animal models were compared to human reference values. Kidneys in TTRhRen mice, SHR and the nonclipped kidneys in 2K1C rats had no sign of hyalinosis, FSGS or GGS. Glomerulopathy in these groups was limited to variations in mesangial and capillary compartment volumes, with mild increases in collagen deposition. Histopathology in angiotensin II infused mice corresponded to mesangioproliferative glomerulonephritis, but not hypertensive glomerulosclerosis. The number of nephrons was significantly reduced in TTRhRen mice and SHR, but did not correlate with severity of glomerulopathy. The most substantial human-like glomerulosclerotic lesions, including FSGS, ischemic obsolescent glomeruli and GGS, were found in the clipped kidneys of 2K1C rats. The comparison of affected kidneys to healthy control in animals produces lesion values that are numerically impressive but correspond to mild damage if compared to humans. Animal studies should be standardized by employing the criteria and classifications established in human pathology to make experimental and human data fully comparable for comprehensive analysis and model improvements.

ANG II and Aldosterone Acting Centrally Participate in the Enhanced Sodium Intake in Water-Deprived Renovascular Hypertensive Rats

Renovascular hypertension is a type of secondary hypertension caused by renal artery stenosis, leading to an increase in the renin–angiotensin–aldosterone system (RAAS). Two-kidney, 1-clip (2K1C) is a model of renovascular hypertension in which rats have an increased sodium intake induced by water deprivation (WD), a common situation found in the nature. In addition, a high-sodium diet in 2K1C rats induces glomerular lesion. Therefore, the purpose of this study was to investigate whether angiotensin II (ANG II) and/or aldosterone participates in the increased sodium intake in 2K1C rats under WD. In addition, we also verified if central AT1 and mineralocorticoid receptor blockade would change the high levels of arterial pressure in water-replete (WR) and WD 2K1C rats, because blood pressure changes can facilitate or inhibit water and sodium intake. Finally, possible central areas activated during WD or WD followed by partial rehydration (PR) in 2K1C rats were also investigated. Male Holtzman rats (150–180 g) received a silver clip around the left renal artery to induce renovascular hypertension. Six weeks after renal surgery, a stainless-steel cannula was implanted in the lateral ventricle, followed by 5–7 days of recovery before starting tests. Losartan (AT1 receptor antagonist) injected intracerebroventricularly attenuated water intake during the thirst test. Either icv losartan or RU28318 (mineralocorticoid receptor antagonist) reduced 0.3 M NaCl intake, whereas the combination of losartan and RU28318 icv totally blocked 0.3 M NaCl intake induced by WD in 2K1C rats. Losartan and RU28318 icv did not change hypertension levels of normohydrated 2K1C rats, but reduced the increase in mean arterial pressure (MAP) produced by WD. c-Fos expression increased in the lamina terminalis and in the NTS in WD condition, and increased even more after WD-PR. These results suggest the participation of ANG II and aldosterone acting centrally in the enhanced sodium intake in WD 2K1C rats, and not in the maintenance of hypertension in satiated and fluid-replete 2K1C rats.

Glomerular Volume and Glomerulosclerosis at Different Depths within the Human Kidney

BACKGROUND

Age, CKD risk factors, and kidney function are associated with larger glomerular volume and a higher percentage of globally sclerotic glomeruli. Knowledge of how these associations may differ by cortical depth is limited.

METHODS

To investigate glomerular volume and glomerulosclerosis across different depths of cortex, we studied wedge sections of the renal parenchyma from 812 patients who underwent a radical nephrectomy (for a tumor), separately characterizing glomeruli in the superficial (subcapsular), middle, and deep (juxtamedullary) regions. We compared the association of mean nonsclerotic glomerular volume and of glomerulosclerosis (measured as the percentage of globally sclerotic glomeruli) with age, obesity, diabetes, smoking, kidney function, and structural pathology in the superficial, middle, and deep regions.

RESULTS

The superficial, middle, and deep regions showed significant differences in glomerular volume (0.0025, 0.0031, and 0.0028 µm³, respectively) and in glomerulosclerosis (18%, 7%, and 11%, respectively). There was a marked increase in glomerulosclerosis with age in the superficial region, but larger glomerular volume was not associated with age at any cortical depth. Glomerulosclerosis associated more strongly with arteriosclerosis and ischemic-appearing glomeruli in the superficial region. Hypertension, lower eGFR, and interstitial fibrosis associated with glomerulosclerosis and glomerular volume to a similar extent at any depth. Diabetes and proteinuria more strongly associated with glomerulosclerosis in the deep and middle regions, respectively, but neither associated with glomerular volume differently by depth. Obesity associated more strongly with glomerular volume in the superficial cortex.

CONCLUSIONS

Most clinical characteristic show similar associations with glomerulosclerosis and glomerulomegaly at different cortical depths. Exceptions include age-related glomerulosclerosis, which appears to be an ischemic process and is more predominant in the superficial region.

Nephronectin Regulates Mesangial Cell Adhesion and Behavior in Glomeruli

A critical aspect of kidney function occurs at the glomerulus, the capillary network that filters the blood. The glomerular basement membrane (GBM) is a key component of filtration, yet our understanding of GBM interactions with mesangial cells, specialized pericytes that provide structural stability to glomeruli, is limited. We investigated the role of nephronectin (Npnt), a GBM component and known ligand of α8β1 integrin. Immunolocalization and in situ hybridization studies in kidneys of adult mice revealed that nephronectin is produced by podocytes and deposited into the GBM. Conditional deletion of Npnt from nephron progenitors caused a pronounced increase in mesangial cell number and mesangial sclerosis. Nephronectin colocalized with α8β1 integrin to novel, specialized adhesion structures that occurred at sites of mesangial cell protrusion at the base of the capillary loops. Absence of nephronectin disrupted these adhesion structures, leading to mislocalization of α8β1. Podocyte-specific deletion of Npnt also led to mesangial sclerosis in mice. These results demonstrate a novel role for nephronectin and α8β1 integrin in a newly described adhesion complex and begin to uncover the molecular interactions between the GBM and mesangial cells, which govern mesangial cell behavior and may have a role in pathologic states.

Spontaneous one-kidney rats are more susceptible to develop hypertension by DOCA-NaCl and subsequent kidney injury compared with uninephrectomized rats

There is little clinical data of how hypertension may influence individuals with nephron deficiency in the context of being born with a single kidney. We recently developed a new rat model (the heterogeneous stock-derived model of unilateral renal agenesis rat) that is born with a single kidney and exhibits progressive kidney injury and decline in kidney function with age. We hypothesized that DOCA-salt would induce a greater increase in blood pressure and therefore accelerate the progression of kidney injury in rats born with a solitary kidney compared with rats that have undergone unilateral nephrectomy. Time course evaluation of blood pressure, kidney injury, and renal hemodynamics was performed in the following six groups of animals from weeks 13 to 18: 1) DOCA-treated rats with a solitary kidney (DOCA+S group), 2) placebo-treated rats with a solitary kidney, 3) DOCA-treated control rats with two kidneys (DOCA+C group), 4) placebo-treated control rats with two kidneys, 5) DOCA-treated rats with two kidneys that underwent uninephrectomy (DOCA+UNX8 group), and 6) placebo-treated rats with two kidneys that underwent uninephrectomy. DOCA+S rats demonstrated a significant rise (P < 0.05) in blood pressure (192 ± 4 mmHg), proteinuria (205 ± 31 mg/24 h), and a decline in glomerular filtration rate (600 ± 42 μl·min(-1)·g kidney weight(-1)) relative to the DOCA+UNX8 (173 ± 3 mmHg, 76 ± 26 mg/24 h, and 963 ± 36 μl·min(-1)·g kidney weight(-1)) and DOCA+C (154 ± 2 mmHg, 7 ± 1 mg/24 h, and 1,484 ± 121 μl·min(-1)·g kidney weight(-1)) groups. Placebo-treated groups showed no significant change among the three groups. An assessment of renal injury markers via real-time PCR/Western blot analysis and histological analysis was concordant with the measured physiological parameters. In summary, congenital solitary kidney rats are highly susceptible to the induction of hypertension compared with uninephrectomized rats, suggesting that low nephron endowment is an important driver of elevated blood pressure, hastening nephron injury through the transmission of elevated systemic blood pressure and thereby accelerating decline in kidney function.

Predicted effects of nitric oxide and superoxide on the vasoactivity of the afferent arteriole

We expanded a published mathematical model of an afferent arteriole smooth muscle cell in rat kidney (Edwards A, Layton, AT. Am J Physiol Renal Physiol 306: F34-F48, 2014) to understand how nitric oxide (NO) and superoxide (O(2)(-)) modulate the arteriolar diameter and its myogenic response. The present model includes the kinetics of NO and O(2)(-) formation, diffusion, and reaction. Also included are the effects of NO and its second messenger cGMP on cellular Ca²⁺ uptake and efflux, Ca²⁺-activated K⁺ currents, and myosin light chain phosphatase activity. The model considers as well pressure-induced increases in O(2)(-) production, O(2)(-)-mediated regulation of L-type Ca²⁺ channel conductance, and increased O(2)(-) production in spontaneous hypertensive rats (SHR). Our results indicate that elevated O(2)(-) production in SHR is sufficient to account for observed differences between normotensive and hypertensive rats in the response of the afferent arteriole to NO synthase inhibition, Tempol, and angiotensin II at baseline perfusion pressures. In vitro, whether the myogenic response is stronger in SHR remains uncertain. Our model predicts that if mechanosensitive cation channels are not modulated by O(2)(-), then fractional changes in diameter induced by pressure elevations should be smaller in SHR than in normotensive rats. Our results also suggest that most NO diffuses out of the smooth muscle cell without being consumed, whereas most O(2)(-) is scavenged, by NO and superoxide dismutase. Moreover, the predicted effects of superoxide on arteriolar constriction are not predominantly due to its scavenging of NO.

Hemodynamic basis for the limited renal injury in rats with angiotensin II-induced hypertension

ANG II is thought to increase the susceptibility to hypertension-induced renal disease (HIRD) via blood pressure (BP)-dependent and BP-independent pathways; however, the quantitative relationships between BP and HIRD have not been examined in ANG II-infused hypertensive rats. We compared the relationship between radiotelemetrically measured BP and HIRD in Sprague-Dawley rats (Harlan) chronically administered ANG II (300-500 ng·kg(-1)·min(-1), n = 19) for 4 wk versus another commonly employed pharmacological model of hypertension induced by the chronic administration of N(ω)-nitro-l-arginine methyl ester (l-NAME, 50 mg·kg(-1)·day(-1), n = 23). [DOSAGE ERROR CORRECTED]. Despite the significantly higher average systolic BP associated with ANG II (191.1 ± 3.2 mmHg) versus l-NAME (179.9 ± 2.5 mmHg) administration, the level of HIRD was very modest in the ANG II versus l-NAME model as evidenced by significantly less glomerular injury (6.6 ± 1.3% vs. 11.3 ± 1.5%, respectively), tubulointerstitial injury (0.3 ± 0.1 vs. 0.7 ± 0.1 injury score, respectively), proteinuria (66.3 ± 10.0 vs. 117.5 ± 10.1 mg/day, respectively), and serum creatinine levels (0.5 ± 0.04 vs. 0.9 ± 0.07 mg/dl, respectively). Given that HIRD severity is expected to be a function of renal microvascular BP transmission, BP-renal blood flow (RBF) relationships were examined in additional conscious rats administered ANG II (n = 7) or l-NAME (n = 8). Greater renal vasoconstriction was observed during ANG II versus l-NAME administration (41% vs. 23% decrease in RBF from baseline). Moreover, administration of ANG II, but not l-NAME, led to a unique BP-RBF pattern in which the most substantial decreases in RBF were observed during spontaneous increases in BP. We conclude that the hemodynamic effects of ANG II may mediate the strikingly low susceptibility to HIRD in the ANG II-infused model of hypertension in rats.

Superoxide dismutase mimetic, tempol, aggravates renal injury in advanced-stage stroke-prone spontaneously hypertensive rats

OBJECTIVE

The aim of this study was to determine whether antioxidant therapy could relieve hypertension and retard the progression of renal damage in advanced-stage hypertensive rats.

METHODS

Twenty-four-week-old spontaneously hypertensive stroke-prone rats were treated for 8 weeks with the superoxide dismutase mimetic tempol, low-dose or high-dose candesartan (an angiotensin receptor blocker), or hydralazine, and blood pressure and renal damage were compared.

RESULTS

Elevated blood pressure and renal damage with heterogeneity were present after 8 weeks, with greater glomerulosclerosis in the juxtamedullary glomeruli than in the superficial glomeruli. Although both tempol and candesartan effectively reduced reactive oxygen species production in the kidney, tempol did not decrease blood pressure and exacerbated urine protein and histological damage, such as glomerulosclerosis and interstitial fibrosis, particularly in juxtamedullary nephrons (tempol vs. untreated: glomerulosclerosis index, 2.0 vs. 1.5, P<0.01; fibrosis, 15 vs. 10%, P<0.001). In contrast, high-dose candesartan and hydralazine prevented these forms of renal damage with lowering blood pressure. Low-dose candesartan also prevented this renal damage without lowering blood pressure. Moreover, there were increased numbers of larger and smaller glomeruli in the juxtamedullary cortex of tempol-treated rats, suggesting that changes in glomerular hemodynamics may be responsible for the exacerbation of glomerulosclerosis. Both candesartan- and hydralazine-treated rats had glomeruli that were slightly decreased in size.

CONCLUSION

These results suggest that single-antioxidant therapy starting at an advanced-stage may be ineffective for hypertension and rather exacerbate renal damage in nonsalt loaded SHRSP. Furthermore, lowering blood pressure and inhibiting the renin-angiotensin system could be critical for slowing the progression of hypertensive renal damage at an advanced stage.

Relaxin does not improve Angiotensin II-induced target-organ damage

Relaxin is a corpus-luteum produced protein hormone with vasodilatatory, anti-fibrotic, and angiogenic properties that are opposite to angiotensin (Ang) II. We investigated whether or not relaxin ameliorates Ang II-induced target-organ damage. We used double transgenic rats harboring both human renin and angiotensinogen genes (dTGR) that develop severe hypertension, target-organ damage, and die untreated within 7–8 weeks. Recombinant relaxin at a low (26 μg/kg/d) and a high dose (240 μg/kg/d) was given to 4 week-old dTGR and age-matched Sprague-Dawley rats (SD). Systolic blood pressure increased progressively in untreated dTGRs from 162±3 mmHg at week 5 to 225±5 mmHg at week 7. Relaxin had no effect on blood pressure whereas SD rats were normotensive (106±1 mmHg). Untreated and relaxin-treated dTGR had similarly severe cardiac hypertrophy indices. Relaxin did not ameliorate albuminuria and did not prevent matrix-protein deposition in the heart and kidney in dTGR. Finally, relaxin treatment did not reduce mortality. These data suggest that pharmacological doses of relaxin do not reverse severe effects of Ang II.

Development of structural kidney damage in spontaneously hypertensive rats

The spontaneously hypertensive rat (SHR) is one of the major models of hypertension. This article describes the current state of knowledge about the mechanism behind kidney damage in SHR in the context of human hypertension and hypertensive kidney disease. It will argue that hypertensive damage in the SHR is pressure-dependent and shows how initial vascular damage leads to a loss of autoregulation and arterial hypertrophy in the juxtamedullary cortex while the outer cortical structures are relatively protected. Progressive arteriolar media hypertrophy then leads to the collapse of some glomeruli followed by tubular atrophy. The reduced glomerular filtration, thus, leads to compensatory hyperfiltration in another population of glomeruli which develop proteinuria and glomerulosclerosis. This model provides some important questions for future research. The regulation of media hypertrophy will be of great interest, as it might slow nephron loss and interstitial fibrosis. Finally, the mechanism by which reduced tubular flow leads to tubular atrophy is another important area for future research. Initial findings indicate that cilia activation may be of major importance for maintaining tubular structure.

Evaluation of renal biopsies in type 2 diabetic patients with kidney disease: a clinicopathological study of 216 cases

OBJECTIVES

The outcome and the therapy of patients with diabetes mellitus (DM), diabetic nephropathy (DN), and non-diabetic renal disease (NDRD) are quite different, so the differential diagnosis is of considerable importance. To evaluate the usefulness of renal biopsy in type 2 diabetic patients, we examined the relationship between the clinical parameters and the histopathological findings in different age groups.

METHODS

Renal biopsy specimens and clinical and laboratory data from 216 patients with type 2 DM were evaluated. According to their age, three groups were defined: 17-35 years (group I), 36-59 years (group II), and more than 60 years (group III).

RESULTS

The study showed that, beside the duration of diabetes, other clinical parameters were not significantly different between the three groups. Chronic nephritic syndrome was the most common clinical manifestation in group I (44.1 %) and in group II (34.0 %). Among patients in group III, we found a high prevalence of chronic renal failure (34.3 %) and nephrotic syndrome (28.6 %). Consistent with the clinical manifestations, IgA nephropathy was the most common pathologic finding in group I (29.4 %) and in group II (34.7 %), whereas the most frequent abnormalities in group III were membranous nephropathy (25.7 %) and tubulointerstitial lesions (14.3 %). Overall, among these patients, 14 cases were diagnosed with DN (6.5 %), 179 with NDRD (82.9 %), while 23 had concurrent DN and NDRD (10.7 %).

CONCLUSIONS

Our results indicated that the clinical manifestations and pathologic findings in type 2 diabetic patients in different age groups have different features. This study emphasized the usefulness of renal biopsy for determining the pattern of renal damage and thus for the overall management of type 2 diabetic patients.

Fasting induces the expression of PGC-1α and ERR isoforms in the outer stripe of the outer medulla (OSOM) of the mouse kidney

BACKGROUND

Peroxisome proliferator-activated receptor-γ co-activator-1α (PGC-1α) is a member of the transcriptional coactivator family that plays a central role in the regulation of cellular energy metabolism under various physiological stimuli. During fasting, PGC-1α is induced in the liver and together with estrogen-related receptor a and γ (ERRα and ERRγ, orphan nuclear receptors with no known endogenous ligand, regulate sets of genes that participate in the energy balance program. We found that PGC-1α, ERRα and ERRγ was highly expressed in human kidney HK2 cells and that PGC-1α induced dynamic protein interactions on the ERRα chromatin. However, the effect of fasting on the expression of endogenous PGC-1α, ERRα and ERRγ in the kidney is not known.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we demonstrated by qPCR that the expression of PGC-1α, ERRα and ERRγ was increased in the mouse kidney after fasting. By using immunohistochemistry (IHC), we showed these three proteins are co-localized in the outer stripe of the outer medulla (OSOM) of the mouse kidney. We were able to collect this region from the kidney using the Laser Capture Microdissection (LCM) technique. The qPCR data showed significant increase of PGC-1α, ERRα and ERRγ mRNA in the LCM samples after fasting for 24 hours. Furthermore, the known ERRα target genes, mitochondrial oxidative phosphorylation gene COX8H and the tricarboxylic acid (TCA) cycle gene IDH3A also showed an increase. Taken together, our data suggest that fasting activates the energy balance program in the OSOM of the kidney.

Increased dietary NaCl potentiates the effects of elevated prorenin levels on blood pressure and organ disease

BACKGROUND

Rats with several 100-fold elevation of plasma prorenin levels due to liver-specific expression of a rat prorenin transgene have cardiac and aortic hypertrophy, renal lesions, and myocardial fibrosis. The effect of increased dietary NaCl on the phenotype of prorenin transgenic rats has not been examined.

METHODS AND RESULTS

We compared the effects of 0.3 and 2% dietary NaCl in wild-type and transgenic rats from 3 to 12 months of age. In comparison with wild-type rats, transgenic rats receiving 0.3% dietary NaCl had approximately 1000-fold elevation of prorenin, 1.5-fold to 2.5-fold elevation of renin concentration and activity, wild-type levels of angiotensin II, and were hypertensive with cardiac and aortic hypertrophy, and increased renal glomerular and tubulo-interstitial injury score. In wild-type rats, 2% dietary NaCl reduced angiotensin levels, produced a delayed increase in blood pressure, and caused cardiac hypertrophy and tubulo-interstitial injury. By contrast, 2% NaCl did not reduce angiotensin levels in transgenic rats, potentiated their hypertension, cardiac and aortic hypertrophy, and increased myocardial interstitial and perivascular fibrosis, without effect on glomerular or tubulo-interstitial injury score.

CONCLUSION

Increased dietary NaCl had a greater impact on the phenotype of transgenic than wild-type rats that may have been due, in part, to their hypertension and their failure to suppress angiotensin levels, consequent to their elevated prorenin levels.

Enhanced myogenic response in the afferent arteriole of spontaneously hypertensive rats

Spontaneously hypertensive rats (SHRs) have normal glomerular capillary pressure even though renal perfusion pressure is higher, suggesting that preglomerular vessels exhibit abnormally high resistance. This may be due to increased superoxide (O(2)(-)) production, which contributes to the vasoconstriction in hypertension. We tested the hypothesis that the myogenic response of the afferent arteriole (Af-Art) is exaggerated in SHRs because of increased levels of reactive oxygen species (ROS). Single Af-Arts were microdissected from kidneys of SHRs and Wistar-Kyoto (WKY) rats and microperfused in vitro. When perfusion pressure in the Af-Art was increased stepwise from 60 to 140 mmHg, the luminal diameter decreased by 8.4 + or - 2.9% in WKY Af-Arts but fell by 29.3 + or - 5.6% in SHR Af-Arts. To test whether ROS production is enhanced during myogenic response in SHRs, we measured chloromethyl-dichlorodihydrofluorescein diacetate acetyl ester (CM-H(2)DCFDA) florescence before and after increasing intraluminal pressure from 60 to 140 mmHg. Pressure-induced increases in ROS were fourfold greater in SHR Af-Arts compared with WKY Af-Arts (SHR, 48.0 + or - 2.2%; and WKY, 12.2 + or - 0.3%). To test whether O(2)(-) contributes to the myogenic response in SHRs, either the membrane-permeant O(2)(-) scavenger Tempol or the nox2-based NADPH oxidase (NOX2) inhibitor gp91ds-tat were added to the Af-Art lumen and bath and the myogenic response was tested before and after treatment. Both Tempol (10(-4) M) and gp91ds-tat (10(-5) M) significantly attenuated the pressure-induced constriction in SHR Af-Arts but not in WKY Af-Arts. We conclude that 1) pressure-induced constriction is exaggerated in SHR Af-Arts, 2) NOX2-derived O(2)(-) may contribute to the enhanced myogenic response, and 3) O(2)(-) exerts little influence on the myogenic response under normotensive conditions.

Developmental programming of a reduced nephron endowment: more than just a baby's birth weight

The risk of developing many adult-onset diseases, including hypertension, type 2 diabetes, and renal disease, is increased in low-birth-weight individuals. A potential underlying mechanism contributing to the onset of these diseases is the formation of a low nephron endowment during development. Evidence from the human, as well as many experimental animal models, has shown a strong association between low birth weight and a reduced nephron endowment. However, other animal models, particularly those in which the mother is exposed to elevated glucocorticoids for a short period, have shown a 20-40% reduction in nephron endowment without discernible changes in the birth weight of offspring. Such findings emphasize that a low birth weight is one, but certainly not the only, predictor of nephron endowment and suggests reduced nephron endowment and risk of developing adult-onset disease, even among normal-birth-weight individuals. Recognition of the dissociation between birth weight and nephron endowment is important for future studies aimed at elucidating the role of a reduced nephron endowment in the developmental programming of adult disease.

Renal autoregulation: new perspectives regarding the protective and regulatory roles of the underlying mechanisms

When the kidney is subjected to acute increases in blood pressure (BP), renal blood flow (RBF) and glomerular filtration rate (GFR) are observed to remain relatively constant. Two mechanisms, tubuloglomerular feedback (TGF) and the myogenic response, are thought to act in concert to achieve a precise moment-by-moment regulation of GFR and distal salt delivery. The current view is that this mechanism insulates renal excretory function from fluctuations in BP. Indeed, the concept that renal autoregulation is necessary for normal renal function and volume homeostasis has long been a cornerstone of renal physiology. This article presents a very different view, at least regarding the myogenic component of this response. We suggest that its primary purpose is to protect the kidney against the damaging effects of hypertension. The arguments advanced take into consideration the unique properties of the afferent arteriolar myogenic response that allow it to protect against the oscillating systolic pressure and the accruing evidence that when this response is impaired, the primary consequence is not a disturbed volume homeostasis but rather an increased susceptibility to hypertensive injury. It is suggested that redundant and compensatory mechanisms achieve volume regulation, despite considerable fluctuations in distal delivery, and the assumed moment-by-moment regulation of renal hemodynamics is questioned. Evidence is presented suggesting that additional mechanisms exist to maintain ambient levels of RBF and GFR within normal range, despite chronic alterations in BP and severely impaired acute responses to pressure. Finally, the implications of this new perspective on the divergent roles of the myogenic response to pressure vs. the TGF response to changes in distal delivery are considered, and it is proposed that in addition to TGF-induced vasoconstriction, vasodepressor responses to reduced distal delivery may play a critical role in modulating afferent arteriolar reactivity to integrate the regulatory and protective functions of the renal microvasculature.

Vascular calcium channels and high blood pressure: pathophysiology and therapeutic implications

Long-lasting Ca(2+) (Ca(L)) channels of the Ca(v)1.2 gene family are heteromultimeric structures that are minimally composed of a pore-forming alpha(1C) subunit and regulatory beta and alpha(2)delta subunits in vascular smooth muscle cells. The Ca(L) channels are the primary pathways for voltage-gated Ca(2+) influx that trigger excitation-contraction coupling in small resistance vessels. Notably, vascular smooth muscle cells of hypertensive rats show an increased expression of Ca(L) channel alpha(1C) subunits, which is associated with elevated Ca(2+) influx and the development of abnormal arterial tone. Indeed, blood pressure per se appears to promote Ca(L) channel expression in small arteries, and even short-term rises in pressure may alter channel expression. Membrane depolarization has been shown to be one stimulus associated with elevated blood pressure that promotes Ca(L) channel expression at the plasma membrane. Future studies to define the molecular processes that regulate Ca(L) channel expression in vascular smooth muscle cells will provide a rational basis for designing antihypertensive therapies to normalize Ca(L) channel expression and the development of anomalous vascular tone in hypertensive pathologies.

Development of diabetic nephropathy in the Milan normotensive strain, but not in the Milan hypertensive strain: possible permissive role of hemodynamics

BACKGROUND

Rats of the Milan normotensive strain develop spontaneous glomerulosclerosis, whereas those of the Milan hypertensive strain are resistant to renal disease, possibly due to intrarenal artery hypertrophy protecting from systemic hypertension. To assess the role of hemodynamic versus metabolic factors in diabetic nephropathy, we investigated whether streptozotocin-induced diabetes accelerates glomerulosclerosis in Milan normotensive and/or removes (the hemodynamic) protection in Milan hypertensive rats by reducing preglomerular vascular resistance.

METHODS

Diabetic and nondiabetic Milan normotensive, hypertensive, and progenitor Wistar rats were followed for 6 months for the assessment of renal function and structure.

RESULTS

Proteinuria increased in nondiabetic and diabetic normotensive and, to a lesser extent, in diabetic Wistar, but not hypertensive rats. Serum creatinine increased and creatinine clearance decreased in nondiabetic and diabetic normotensive rats at 6 months. At 1.5 months, diabetic normotensive, but not hypertensive rats showed increased glomerular filtration rate and filtration fraction, suggesting glomerular hypertension. Diabetic nephropathy was detected in diabetic normotensive and Wistar, but not hypertensive rats. Glomerular extracellular matrix and TGF-beta mRNA levels increased with diabetes (and age) in normotensive, but not hypertensive rats. Arterioles and interlobular arteries showed increased media thickness in hypertensive versus normotensive rats, with diabetes reducing it only in the normotensive.

CONCLUSION

These data show that Milan hypertensive rats are not susceptible to diabetic nephropathy, at variance with glomerulosclerosis-prone Milan normotensive rats, thus indicating the importance of genetic background. Our study suggests that the nature of this (genetic) protection might be hemodynamic, with intrarenal artery hypertrophy preventing diabetes-induced loss of autoregulation.

Glomerular and tubular damage in normotensive and hypertensive rats

Tubular cell damage is an important mediator of interstitial fibrosis in chronic renal diseases. Glomerular and tubular damage in genetic hypertension was therefore studied. Tubular and glomerular damage was investigated in 10-, 40-, and 70-wk-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) and compared with glomerular capillary pressure (P(GC)) and glomerulosclerosis in superficial (OC) and juxtamedullary (JMC). Tubular vimentin was used as criterion of tubular damage. Variation in tubular diameter was measured during change in perfusion pressure, and ureter ligation was used to demonstrate the relationship between tubular pressure and appearance of vimentin-positive cells. Tubular and glomerular damage was most pronounced in JMC and greater in SHR than in WKY. It was absent in 10-wk-old WKY and significantly higher in JMC of SHR compared with WKY at 70 wk of age. Numbers of vimentin-positive segments were 18 +/- 9 vs. 38 +/- 7% in JMC of 70-wk-old WKY and SHR (P < 0.02), and glomerulosclerosis was seen in 8 +/- 3 vs. 19 +/- 5% of glomeruli in JMC of 70-wk-old WKY and SHR, respectively (P < 0.01). P(GC) was 45 +/- 3 mmHg in JMC of WKY and 57 +/- 3 mmHg in JMC of 70-wk-old SHR (P < 0.001). Tubular diameter variation was greatest in SHR (P < 0.05) during pressure variation. Proteinuria was present only in 40- and 70-wk-old SHR and did not correlate with tissue damage. Tubular and glomerular damage in both strains develops in parallel and may be caused by a common mechanism, which may be glomerular capillary and tubular wall stretch during acute blood pressure variation which is greatest in JMC in SHR.

Transgene of MIF induces podocyte injury and progressive mesangial sclerosis in the mouse kidney

BACKGROUND

Recent evidence suggests that macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that plays a pathogenic role in glomerulonephritis. Renal expression of MIF is up-regulated in infiltrating and intrinsic renal cells, which include glomerular epithelial cells. The aim of the current study was to further clarify the role of MIF produced by podocytes in the process of renal disease.

METHODS

We generated transgenic mice carrying a murine MIF cDNA driven by cytomegalovirus enhancer and beta-actin/beta-globin promoter, a hybrid promoter transactivated in podocytes in vivo.

RESULTS

MIF expression was markedly up-regulated in podocytes in neonatal and adult transgenic kidneys. A longitudinal study of the MIF transgenic mice demonstrated a progressive matrix increase in mesangium accompanied by collagen IV accumulation, representing no significant glomerular cell hypercellularity. The glomeruli in transgenic kidney were not accompanied by influx of macrophages and T cells at the early stage of disease progression. Although a significant number of the mice showing higher expression of MIF died from renal failure at 8 weeks, most of them survived with significant proteinuria and progressive renal failure. Podocytes of transgenic mice frequently underwent characteristic ultrastructural changes, such as cell flattening, contracted foot processes, and villous transformation. In addition, immunohistochemical expression of synaptopodin, an actin-associated protein distributed in differentiated podocyte foot process, was significantly attenuated in transgenic kidney.

CONCLUSION

Our results indicate that podocyte-expressed MIF could induce an injury of podocytes themselves, thereby accelerating the progression of glomerulosclerosis and leading to end-stage renal failure.

Time-course genetic analysis of albuminuria in Dahl salt-sensitive rats on low-salt diet

The Dahl salt-sensitive hypertensive (S) rat develops albuminuria early in life even on a low-salt diet. In contrast, the spontaneously hypertensive rat (SHR) is highly resistant to developing albuminuria despite elevated BP. An F(1) hybrid of S and SHR showed a low urinary albumin excretion (UAE) and low urinary protein excretion (UPE) similar to SHR, i.e., SHR was dominant. A genetic analysis was carried out on a large population (n = 276) obtained by backcrossing F(1) rats to the recessive S strain; the population was fed a low-salt diet. Genome scans done at 8, 12, and 16 wk of age yielded ten quantitative trait loci (QTL) for UAE and/or UPE with variable time-course patterns on nine rat chromosomes (RNO), i.e., RNO1, RNO2, RNO6, RNO8, RNO9, RNO10, RNO11, RNO13, and RNO19. There were two UPE QTL on RNO6. At most of the UAE and/or UPE QTL, the S allele was associated with increased excretion, except for one of the QTL on RNO6 and the QTL on RNO11, where the S allele caused decreased excretion. Only the UAE and UPE QTL on RNO10 co-localized with a BP QTL. The S allele on RNO10 caused higher BP and higher UAE. Two additional BP QTL were detected on RNO1 and RNO6. Most of the UAE and UPE QTL co-localized with QTL for kidney lesions characteristic of S rats. Multiple interactions were observed for UAE, many of which involved RNO2. In summary, UAE is highly polygenic and the majority of the QTL altering UAE do not co-localize with QTL for BP as evaluated by tail-cuff measurements of BP.

Attenuated buffering of renal perfusion pressure variation in juxtamedullary cortex in SHR

Renal tissue damage is substantially more pronounced in the juxtamedullary than in the superficial cortex in hypertensive rats, and the pathogenesis of the morphological changes are only partly understood. Glomerular capillary pressure (P(GC)) is increased, and steady-state autoregulation is normal in the deep renal cortex. We tested the hypothesis that the transient period from one pressure level to another may induce greater variation in local perfusion before stable autoregulation is established. An acute increase in local perfusion was compared in the superficial and juxtamedullary cortex of spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY) after an abrupt increase in perfusion pressure. Total renal blood flow (RBF) was measured by a Transonic flow probe and local renal perfusion by laser Doppler flowmetry. Renal perfusion pressure was lowered to 50% of initial values and released abruptly. The maximal RBF increased from 6.3 +/- 0.4 to a maximal value of 7.6 +/- 0.3 ml/min (P < 0.001) in SHR and from 7.3 +/- 0.3 to 8.2 +/- 0.6 ml/min (P < 0.001) in WKY. These changes were not significantly different from each other. The change in superficial cortical perfusion was also not different between SHR and WKY. Pressure release increased juxtamedullary perfusion in SHR from 146 +/- 8 to a maximal value of 228 +/- 17 units (P < 0.001) and in WKY from 160 +/- 13 to 179 +/- 11 units (P < 0.001). The results were significantly different from each other (P < 0.001). The time for maximal flow response was shorter in the deep cortex of SHR, and the time for normalization was longer than in WKY. These data indicate that the buffering of perfusion pressure variation is significantly attenuated in the juxtamedullary cortex, and significantly more so in SHR than in WKY, assuming a covariation of RBF and P(GC), and this finding may explain the extensive morphological damage in the juxtamedullary cortex of SHR.

Tubulointerstitial injury of Thy-1 nephritis in uninephrectomized stroke-prone spontaneously hypertensive rats

Thy-1 nephritis was induced in stroke-prone spontaneously hypertensive rats (SHR-SP) with unilateral nephrectomy (UNX) and normotensive same genetic strain Wistar-Kyoto (WKY) rats with UNX to evaluate whether the tubulointerstitial injury in Thy-1 nephritis is accelerated by long-term systemic and intraglomerular hypertension. SHR-SP that underwent UNX at twelve weeks of age were randomly assigned to receive monoclonal anti-thy 1.1 antibody (group SP), and normal saline (group SC). Age-matched normotensive WKY rats served as controls and were given the same dose of monoclonal anti-thy 1.1 antibody after UNX (group WK). In all groups, the blood pressure and renal function were assessed, and morphologic changes of tubulointerstitium were examined by using immunohistochemistry and light microscopy twelve weeks after Thy-1 nephritis induction (in groups SP and WK) and UNX alone (in group SC). In all groups, histological findings, the degree of monocyte/macrophage infiltration, interstitial expression of alpha-smooth muscle actin (alpha-SMA), which is a marker for myofibroblasts, and the degree of tubular cell proliferation were examined. In addition, assessments of blood pressure, serum creatinine and BUN levels, and the degree of proteinuria were made. In parallel to glomerular structural damage, interstitial fibrosis with predominant monocyte/macrophage influx, increased interstitial expression of alpha-SMA and tubular cell proliferation were observed in group SP. A significant increase in serum creatinine and proteinuria were also present in this group. In contrast, the changes observed in group SC were not so evident or extensive as in group SP. The level of proteinuria was lower than that in group SP. No evident tubulointerstitial changes were found in group WK. The results showed that tubulointerstitial injury was prominently progressed in the hypertensive model with Thy-1 nephritis. This suggests that sustained systemic and glomerular hypertension is not only ultimately responsible for the progression of immunologically mediated glomerular injury, but is also responsible for subsequent tubulointerstitial changes. Migration and proliferation of myofibroblasts and intense influx of monocytes/macrophages may contribute to the development of tubulointerstitial fibrosis.

Effect of angiotensin II blockade on renal injury in mineralocorticoid-salt hypertension

Kidney function and structure were compared in control rats (group 1) and in 3 groups of rats made hypertensive by administration of aldosterone and saline for 8 weeks (groups 2, 3, and 4). Group 2 rats received only aldosterone and saline, while group 3 also received losartan and group 4 also received enalapril. Rats in all groups were subjected to uninephrectomy before beginning the experiment. Hypertension and proteinuria in rats given aldosterone and saline were not affected by losartan or enalapril (8-week values for blood pressure in mm Hg: 135+/-3 group 1, 193+/-4 group 2, 189+/-4 group 3, 189+/-5 group 4; P<0.05 groups 2, 3, and 4 versus 1; 8-week values for proteinuria in mg/d: 44+/-8 group 1, 278+/-34 group 2, 267+/-37 group 3, 289+/-36 group 4; P<0.05 groups 2, 3, and 4 versus 1). Vascular, glomerular, and tubulointerstitial injury accompanied hypertension and proteinuria at 8 weeks. Losartan and enalapril did not prevent vascular injury, which was characterized by thickening of arterial and arteriolar walls and by fibrinoid necrosis and thrombotic microangiopathy. Likewise, losartan and enalapril did not reduce the prevalence of glomerular segmental sclerosis (1+/-1% group 1, 10+/-2% group 2, 11+/-2% group 3, 13+/-2% group 4; P<0.05 groups 2, 3, and 4 versus 1) or limit tubulointerstitial injury as reflected by the volume fraction of the cortical interstitium (15+/-1% group 1, 20+/-1% group 2, 21+/-1% group 3, 21+/-1% group 4; P<0.05 groups 2, 3, and 4 versus 1). These findings suggest that local angiotensin II activity does not contribute to the development of renal injury in mineralocorticoid-salt hypertension.

Daily exercise attenuates the development of arterial blood pressure related cardiovascular risk factors in hypertensive rats

This study was designed to test the hypothesis that daily spontaneous running (DSR) attenuates the development of blood pressure-related cardiovascular disease risk factors (BP-related CVD risk factors) in spontaneously hypertensive rats (SHR). After 8 weeks of DSR or sedentary control, rats were chronically instrumented with arterial catheters. Daily exercise attenuated the development of all measures of BP-related CVD risk factors. Specifically DSR attenuated the increase in systolic blood pressure (delta--22 mmHg), systolic blood pressure variability (delta--2.5 mmHg), and systolic blood pressure load (delta--27%). Similarly, DSR attenuated the increase in diastolic blood pressure (delta--15 mmHg), diastolic blood pressure variability (delta--1.19 mmHg), and diastolic blood pressure load (delta--17%). Finally, DSR attenuated the development of tachycardia (delta--63 bpm). These data demonstrate that daily exercise attenuates the development of hypertension and tachycardia in animals predisposed to hypertension.

Extracellular matrix deposition and cell proliferation in a model of chronic glomerulonephritis in the rat

BACKGROUND

Resident glomerular cell proliferation, matrix deposition and secretion of matrix metalloproteinases play a major role in the progression of chronic glomerular disease. These features were studied in a novel approach in a rat model of chronic glomerulonephritis induced by four injections of an anti-Thy 1.1 antiserum at weekly intervals.

METHODS

Chronic immune mediated mesangial injury was induced in male Sprague-Dawley rats by repeated intravenous injection of an anti-Thy 1.1 antiserum. One week after the first and fourth injection of the antiserum proteinuria was evaluated and the kidneys were removed. Immunohistology was performed for proliferating cells, monocytes and collagen type IV. Furthermore, mRNA expression of collagen type IV, TGF-beta and the matrix degrading enzyme MMP-2 as well as MMP-2 protein expression were studied.

RESULTS

Urinary protein excretion was dramatically increased after one antiserum injection and stayed elevated at a lower level after the fourth antiserum injection. After the initial induction of nephritis, 7 days following antiserum, resident glomerular cell proliferation was increased whereas with repeated injections of the antiserum cell numbers were not different from controls, as measured 1 week after the fourth injection. In contrast, extracellular matrix accumulation (collagen type IV) increased after the first antiserum injection and further increased after the fourth antiserum injection. The mRNA expression for collagen type IV increased after the first antiserum injection and showed further increase after the fourth antiserum injection. Induction of nephritis also stimulated glomerular mRNA expression of MMP-2 and TGF-beta, both of which remained at a high level after the fourth antiserum injection. Glomerular protein levels of MMP-2 also increased after the first antiserum injection and showed a further slight increase after the fourth injection.

CONCLUSION

Increased cellular proliferation is involved in an early stage of this disease, while enhanced expression of glomerular matrix and augmented mRNA and protein expression of the matrix degrading enzyme MMP-2 continue into the chronic phase, and contribute to the extensive structural remodeling process that accompanies this form of glomerular injury.

Monocyte chemoattractant protein-1 mediates collagen deposition in experimental glomerulonephritis by transforming growth factor-beta

BACKGROUND

Monocyte chemoattractant protein-1 (MCP-1) plays a significant role in the recruitment of monocytes/macrophages in experimental glomerulonephritis (GN). Because recent evidence points to possible profibrogenic effects of leukocyte-derived factors in GN, this study was designed to evaluate the role of the chemokine MCP-1 in the fibrogenesis of experimental GN.

METHODS

Rats with an anti-thy-1-induced GN were treated with a neutralizing antiserum against MCP-1. Glomerular collagen type IV, as a marker of glomerular matrix deposition, was assessed by Northern and Western blotting and immunohistology. Transforming growth factor-beta (TGF-beta), an important mediator of this matrix expansion, was studied by Northern and Western blotting.

RESULTS

The induction of GN resulted in a significant increase of glomerular collagen type IV deposition and TGF-beta synthesis. The neutralization of MCP-1 significantly reduced the enhanced collagen type IV protein synthesis and deposition without affecting collagen mRNA expression. However, both the enhanced transcription and protein synthesis of TGF-beta were inhibited by anti-MCP-1 antiserum in nephritic animals.

CONCLUSIONS

In this model of GN, MCP-1 has a fibrogenic effect through the stimulation of TGF-beta. MCP-1 is thus not only important for the recruitment of inflammatory cells, but also mediates glomerular matrix accumulation.

Increased glomerular capillary pressure and size mediate glomerulosclerosis in SHR juxtamedullary cortex

To gain insight into the mechanisms in the development of glomerulosclerosis in juxtamedullary cortex, the degree of glomerulosclerosis, glomerular tuft diameter, glomerular capillary pressure (Pgc), and local renal blood flow (RBF) autoregulation were measured in superficial and juxtamedullary cortex of 10- and 70-wk-old spontaneously hypertensive rat (SHR), using aged matched Wistar-Kyoto (WKY) rats as controls. Pgc was measured after corticotomy by direct micropuncture of glomeruli in superficial and juxtamedullary cortex. Total RBF was measured by a transit-time flowmeter (Transonic) and local blood flow by use of laser-Doppler flowmetry. The degree of glomerulosclerosis measured by a semiquantitative histological technique was significantly increased in juxtamedullary compared with superficial cortex in all groups. The difference was most pronounced in the juxtamedullary cortex of 70-wk-old SHR. Pgc was significantly increased in juxtamedullary cortex compared with superficial cortex in 70-wk SHR (57.1 +/- 2.7 vs. 46.5 +/- 0.5 mmHg, P < 0.01). The corresponding data set from 70-wk WKY was 45.5 +/- 0.43 vs. 41.6 +/- 1.5 (P < 0.05). The Pgc in juxtamedullary cortex of 10-wk SHR was slightly higher than in superficial cortex (45.1 +/- 2.3 vs. 50.1 +/- 1.2 mmHg, P = 0.05), whereas there was no difference in 10-wk WKY. Glomerular diameter was larger in juxtamedullary cortex in old animals but not significantly different in 10-wk WKY rats and 10-wk SHR. Total RBF was reset to higher perfusion pressures in hypertensive rats. Juxtamedullary and superficial blood flow autoregulation were not significantly different from total RBF autoregulation in all groups. These results suggest that hypertrophy as well as increased Pgc might contribute to the development of manifest glomerulosclerosis. Changes in local blood flow autoregulation do not seem to play a major role in the development of glomerulosclerosis.

Proteinuria precedes cerebral edema in stroke-prone rats: a magnetic resonance imaging study

BACKGROUND AND PURPOSE

Stroke-prone spontaneously hypertensive rats (SHRSP) subjected to high sodium intake develop severe hypertension, cerebral edema, and proteinuria, culminating in organ damage and early death. MRI, which can be applied serially, provides the unique opportunity to study temporal and quantitative relations between these changes and whether diminution of sodium intake can attenuate established cerebral edema.

METHODS

SHRSP were subjected to 1% NaCl in drinking water. Cerebral MRI, proteinuria and systolic blood pressure (SBP) were measured serially. After detection of cerebral edema (T2-weighted MRI), 6 rats were killed for histology, to confirm the diagnosis of cerebral edema. The others were followed up for 7 more days while salt loading was continued (n = 10, group 1) or after sodium intake was normalized (n = 7, group 2).

RESULTS

SHRSP invariably developed cerebral edema in 30 days (range, 8 to 54 days). At this point neurological signs were absent in 16 of 23 rats. SBP rose until 1 week before detection of cerebral edema, and then stabilized at approximately 265 mm Hg. Proteinuria invariably preceded cerebral edema, with a concentration exceeding 40 mg/d predicting development of cerebral edema in 9 days (range, 3 to 15 days). There was linear correlation (R=.62, P<.0001) between proteinuria and cerebral edema (pixels with an intensity above a defined threshold). Rats in group 1 showed an increase in cerebral edema (from 5.8+/-1.1% to 12.5+/-2.8%; P<.05), and proteinuria remained high (from 305+/-44 to 338+/-29 mg/d); and 2 died spontaneously. Rats in group 2 showed no significant change in edema (from 4.9+/-0.5% to 6.9+/-1.3%) but a marked fall in proteinuria (from 294+/-24 to 119+/-10 mg/d; P<.05), both significantly different from group 1 (P<.05); all survived. SBP remained unaltered in both groups.

CONCLUSIONS

Our data establish MRI as a sensitive method for detection of cerebral edema, often prior to neurological signs, in SHRSP. Proteinuria predicts cerebral edema, and these two variables, both obtained noninvasively, are quantitatively related. Moreover, in SHRSP normalizing sodium intake after salt loading attenuates development of cerebral edema and reduces proteinuria.

Pathophysiology and management of progressive renal disease

Recently, the hypothesis that all renal diseases are inherently progressive and self-perpetuating has focused attention on adaptive changes in renal structure and function that occur whenever renal function is reduced. These glomerular adaptations to renal disease include increases in filtration rate, capillary pressure and size, and are referred to as glomerular hyperfiltration, glomerular hypertension and glomerular hypertrophy, respectively. Extrarenal changes, such as dietary phosphate excess, systemic hypertension, hyperlipidaemia, acidosis and hyperparathyroidism occur in animals with renal disease and may be contributors to progression of renal disease. Emphasis in the management of companion animals with renal disease has shifted to identifying, understanding and controlling those processes that play a role in the progression from early to end-stage renal failure. Advances made by veterinary nephrologists in the past 15 years permit resolution of old controversies, formulation of new hypotheses and discussion of unresolved issues about the nature of progressive renal disease in dogs and cats.

Autoregulation of total and zonal glomerular filtration rate in spontaneously hypertensive rats during antihypertensive therapy

The effects of angiotensin II type 1 receptor antagonist (losartan), angiotensin 1-converting enzyme (ACE) inhibitor (enalapril), and calcium channel blocker (nifedipine) on autoregulation of total and zonal glomerular filtration rate (GFR) were studied in spontaneously hypertensive rats (SHRs), 10 and 40 weeks of age, and 10-week-old Wistar-Kyoto (WKY) rats. Untreated animals in each group served as controls. Renal blood flow (RBF) was measured by a transit-time flow probe (Transonic) on the left renal artery. Total and zonal GFR (outer, middle, and inner cortex) were estimated from tubular uptake of 125iodine-labeled aprotinin (125IAp) injected i.v. at control renal arterial pressure (RAP), and 131IAp injected at a RAP reduced to the lower limit of RBF autoregulation. Autoregulation of RBF was reset to higher pressure levels in untreated hypertensive rats. Enalapril normalized this resetting in 10-week-old SHRs, but not in aged SHRs 40 weeks. Losartan did not completely normalize this resetting in either 10-or 40-week-old SHRs, whereas nifedipine impaired RBF autoregulation in both WKYs and SHRs. A decreased autoregulatory compensation of GFR after pressure reduction was observed in losartan-treated 10-week-old SHRs and after all drug regimens in 40-week SHRs. GFR autoregulation in outer, middle, and inner cortex was impaired in losartan-treated 10-and 40-week-old SHRs. With all treatments, the autoregulation in 10- and 40-week-old SHRs was better preserved in the inner than in the outer cortex. The impaired autoregulation may indicate that a part of the dilatory capacity of preglomerular vessels has already been taken out by hypotensive treatment. Renal vascular abnormalities may have an additional effect.

Endothelin antagonism in end-organ damage of spontaneously hypertensive rats. Comparison with angiotensin-converting enzyme inhibition and calcium antagonism

High blood pressure results in cardiac hypertrophy and fibrosis, increased thickness and stiffness of large artery walls, and decreased renal function. The objective of our study was to assess the role of endothelin, angiotensin II, and high blood pressure in the end-organ damage observed in spontaneously hypertensive rats (SHR). For this purpose, SHR were treated for 10 weeks with either a mixed endothelin-A and endothelin-B receptor antagonist, bosentan (100 mg/kg per day), an angiotensin-converting enzyme inhibitor, enalapril (10 mg/kg per day), or a long-acting calcium antagonist, mibefradil (20 mg/kg per day). A group of SHR was left untreated, and a group of normotensive Wistar rats was used as control. At the end of treatment, maximal coronary blood flow was measured in isolated perfused hearts. Cardiac hypertrophy and fibrosis, aortic medial thickness, and extracellular matrix content were evaluated by quantitative morphometry. Proteinuria and urea and creatinine clearances were measured, and renal histopathology was assessed. SHR exhibited cardiac hypertrophy, perivascular fibrosis, and decreased maximal coronary blood flow. Aortic medial thickness was increased, whereas elastin density was decreased. Finally, SHR showed decreased urinary excretion and decreased urea and creatinine clearances. No renal histological lesions were observed. Although bosentan did not affect blood pressure, it normalized renal function and slightly decreased left ventricular hypertrophy and fibrosis. Enalapril and mibefradil were both effective in significantly decreasing blood pressure, left ventricular hypertrophy, and aortic medial thickness and improving coronary blood flow, but in contrast to bosentan, they did not improve creatinine clearance. We conclude that in SHR, high blood pressure plays a major role in end-organ damage and that endothelin may partly mediate renal dysfunction and cardiac remodeling independently of a direct hemodynamic effect.

Prostaglandin E1 inhibits collagen expression in anti-thymocyte antibody-induced glomerulonephritis: possible role of TGF beta

To test whether or not prostaglandins mediate extracellular matrix formation in immune-mediated glomerular disease, rats with anti-thymocyte antibody-induced glomerulonephritis were treated with prostaglandin E1 (PGE1) (250 micrograms/twice daily/s.c.). Glomerular expression of collagen types III and IV was assessed by Northern blotting, immunohistology and Western blotting. Proliferation of glomerular cells was evaluated by staining for the proliferating cell nuclear antigen (PCNA) and consecutive cell counting. At day five after induction of the disease, glomerular mRNA levels of collagen types III and IV were three- to fivefold higher compared with non-nephritic controls. Similarly glomerular deposition of these collagens was markedly increased when assessed by immunohistology. The treatment of nephritic rats with PGE1 reduced the increased glomerular mRNA levels as well as the protein concentration and the deposition of extracellular collagens. The number of PCNA positive cells which was significantly higher in nephritic rats when compared with control animals (24 hr, nephritis 2.53 +/- 0.33 and Control 0.26 +/- 0.06, P = 0.011; 5 days, nephritis 5.10 +/- 1.13 and Control 0.75 +/- 0.08, cells per glomerular cross section, P = 0.03) was reduced by PGE1 (24 hr, nephritis+PGE1 0.44 +/- 0.30, P = 0.0001; 5 days, nephritis +/- PGE1 1.91 +/- 1.84 cells per glomerular cross section, P = 0.001). Prostaglandin E1 also ameliorated the glomerular infiltration of monocytes at 24 hours (nephritis 4.36 +/- 2.82, nephritis + PGE1 2.20 +/- 1.82, cells per glomerular cross section) and five days (nephritis 1.51 +/- 0.58, nephritis+PGE1 1.12 +/- 0.61, cells per glomerular cross section). To further characterize possible mechanisms by which PGE1 reduces extracellular matrix deposition, the glomerular expression of transforming growth factor (TGF-beta), and interleukin 1 beta (IL-1 beta) was assessed by Northern blotting. Nephritic glomeruli showed increased mRNA levels of TGF-beta at day 5 and IL-1 beta at 24 hours when compared with control kidneys. Treatment of the animals with PGE1 inhibited the mRNA expression of TGF-beta and IL-1 beta. These data demonstrate that PGE1 reduces the glomerular expression of extracellular matrix proteins in anti-thymocyte antibody-induced glomerulonephritis, suggesting a beneficial role of prostaglandins in this proliferative glomerular immune injury. The effects of PGE1 might be mediated by inhibition of TGF-beta and IL-1 beta production.

Hypothalamic lesions induce obesity and sex-dependent glomerular damage and increases in blood pressure in rats

Placement of two symmetrical lesions in the ventromedial hypothalamus of the rat causes massive overeating and obesity. We have studied male (n=8) and female (n=5) Munich-Wistar rats 7 months after induction of obesity and compared them with age-matched controls. Body weight and kidney weight were greater in control males versus females (396 +/- 7 and 1.5 +/- 0.1 g versus 229 +/- 4 and 1.0 +/- 0.1 g, respectively; both P <.001). Both obese males and females were heavier than lean counterparts (592 +/- 30 and 361 +/- 19 g, both P <.001), whereas kidney weight was similar between obese and control rats of each sex (obese males, 1.5 +/- 0.1 g; obese females, 1.1 +/- 0.1 g). Blood pressure was higher in obese versus control males; there was no differences between other groups. Single-nephron glomerular filtration rate was similar in control females and males and obese females but depressed in obese males. Glomerular blood pressure was normal in all groups. Urinary protein excretion and the percentage of sclerosed glomeruli were similar in control females and males and obese females but elevated in obese males. Plasma triglyceride levels were elevated in obesity, particularly in males. We conclude that hypothalamic lesioning induces overeating and obesity and selectively in the male causes hypertension and glomerular damage as well as declines in renal function. This injury is not hemodynamically mediated (glomerular blood pressure is normal) but may be related to the elevation in plasma triglyceride levels, which has previously been causally linked to glomerular damage in genetically obese rats.

Renal ablation acutely transforms 'benign' hypertension to 'malignant' nephrosclerosis in hypertensive rats

The present studies examine the consequences of the hemodynamic changes associated with approximately 5/6 renal ablation in the spontaneously hypertensive rat (SHR), a strain that normally does not exhibit evidence of vascular and/or glomerular injury until late in life despite significant hypertension. Control SHR with intact renal mass demonstrated normal renal autoregulation and an absence of vascular or glomerular injury. Renal mass reduction resulted in an initial expected decrease in renal blood flow to the remnant kidney at 5 days (2.8 +/- 0.3 mL/min) compared with control SHR (8.1 +/- 0.7 mL/min) at a mean arterial pressure of approximately 160 mm Hg (P < .01). By 10 to 14 days after renal ablation, marked renal vasodilation was observed (renal blood flow 8.3 +/- 0.8 mL/min at mean arterial pressure of approximately 160 mm Hg) along with severe impairment of autoregulatory ability. Striking and florid vascular injury to interlobular arteries and afferent arterioles had also developed by 10 to 14 days after approximately 5/6 renal ablation in a pattern similar to that observed in "malignant" hypertension, despite systolic blood pressures that were not significantly different from those in control SHR (168.2 +/- 6.4 versus 165.6 +/- 4.7 mm Hg). An additional group of SHR that were made normotensive with a triple-therapy antihypertensive regimen before and after approximately 5/6 renal ablation also exhibited hemodynamic changes similar to those in the untreated rats at 10 to 14 days but did not develop significant vascular or glomerular injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium blockade versus ACE inhibition in clipped and unclipped kidneys of 2K-1C rats

ACE inhibitors have been shown to worsen the kidney damage occurring distal to a renal artery stenosis. To determine if this effect was due to the decrease of arterial pressure or to an inhibition of the formation of angiotensin, we compared the effects of equihypotensive doses of an angiotensin converting enzyme inhibitor (enalapril) and a long-acting calcium antagonist (Ro 40-5967) in 2K-1C rats. The rats were treated for five weeks with either enalapril, Ro 40-5967, or were left untreated. A group of sham operated rats was used as control. At the end of the five-week treatment period, proteinuria, plasma urea and creatinine were measured and quantitative morphometry of the clipped and unclipped kidneys was performed. Ro 40-5967, despite an absence of inhibition of the renin-angiotensin system, worsened the lesions of the clipped kidney to the same extent as enalapril. In contrast, the effects of both drugs on the unclipped kidney were different. Ro 40-5967, and not enalapril, increased the weight and the glomerular surface area of the unclipped kidney. Ro 40-5967 did not change the glomerulosclerosis index, which was improved by enalapril. In contrast with enalapril, Ro 40-5967 decreased plasma urea and creatinine concentrations. Only enalapril decreased proteinuria which originated from the unclipped kidney as shown by nephrectomy experiments. We conclude that during ACE inhibition the fall in renal perfusion pressure seems to be the main determinant of the renal damage distal to a renal artery stenosis, independently of a blockade of the renin-angiotensin system.(ABSTRACT TRUNCATED AT 250 WORDS)

Glomerular filtration and volume regulation in gravid animal models

The gestational increase in glomerular filtration rate that occurs in the normal rat is exclusively the result of an increase in renal plasma flow and there is no sustained increase in glomerular capillary blood pressure during a normal pregnancy. The factor or factors that initiate the gestational renal vasodilatation (and plasma volume expansion) are maternal, not fetoplacental in origin. The precise nature of the initiating factors has not yet been defined, although it is unlikely that the gestational plasma volume expansion can be the sole cause of the increased glomerular filtration rate seen in pregnancy. A number of vasoactive hormones are activated in pregnancy but as yet no clear candidate has emerged as 'the renal vasodilator'. Preliminary evidence suggests that nitric oxide may play an important role in gestational vasodilatation. The normal kidney in pregnancy exhibits substantial renal reserve to amino acid infusion and unimpaired autoregulatory ability despite being already vasodilated by the gestational stimulus. There are marked and sometimes contradictory changes in the various volume sensing and control systems in pregnancy. In general, the sensors perceiving and controlling intravascular volume are reset during a normal pregnancy to enable to mother to accommodate the increased plasma volume without provoking a natriuretic response. Whether the expanded plasma volume of pregnancy is perceived as normal or underfilled is not clear at this time and may vary according to the volume regulatory system. Repetitive pregnancies do not have any cumulative, long-term deleterious effects on renal function, when the underlying function is normal, when it has been compromised by removal of renal mass or during chronic systemic hypertension in the spontaneously hypertensive rat. In the short term, pregnancy does not worsen kidney function when underlying glomerular damage is due to immune stimuli, ablation of renal mass or gentamicin, or in the spontaneously hypertensive rat. Therefore, the chronic renal vasodilatation of pregnancy does not appear to be a damaging entity, unlike other states of low preglomerular arteriolar resistance, studied in the male rat. When pregnancy is superimposed on Adriamycin nephrosis or chronic blockade of nitric oxide, hypertension occurs and renal function declines. In both situations endothelial damage/dysfunction occurs, as is also seen in pre-eclampsia. Further study of the effects of pregnancy in animal models of endothelial dysfunction will prove rewarding.

Early interstitial changes in hypertension-induced renal injury

To elucidate the mechanisms of hypertensive renal injury, we investigated the time course and extent of changes in matrix composition, as well as cell proliferation and infiltration in two-kidney, one clip rats. The nonclipped kidneys from hypertensive and sham-operated control rats (n = 5 to 10 in each group) were studied at 7, 14, 21, and 28 days after clipping. Systolic blood pressure was elevated by day 7 (154 +/- 3 versus 111 +/- 4 mm Hg in sham group, P < .001, n = 10 each). Hypertension resulted in an early expansion of the interstitial volume by 37%, whereas hypertensive vascular changes and glomerular injury did not become evident until day 21. Immunofluorescence studies revealed an early interstitial accumulation of collagens I, III, IV, V, VI, and fibronectin by day 7. In contrast, the glomeruli showed a mild to moderate increase in collagens I, III, IV, V, laminin, and fibronectin but not collagen VI later in the established phase of hypertension. Staining for proliferating cell nuclear antigen as a marker of cell replication was increased in tubular epithelial but not interstitial or glomerular cells. A progressive infiltration of macrophages (16 +/- 2 versus 9 +/- 1 ED1+ cells/mm2, P < .05, n = 6) and T lymphocytes (93 +/- 15 versus 74 +/- 7 CD4+ cells/mm2, n = 8) in the cortical interstitium had already occurred by day 7. On the other hand, only macrophages increased in number within the glomeruli. Thus, renovascular hypertension leads to an early tubular cell proliferation, mononuclear cell recruitment, and deposition of matrix proteins primarily within the interstitium. We conclude that the injury producing nephrosclerosis in this model extends far beyond the glomeruli. Both the tubules and the interstitium are actively involved and may be the more important initial sites of injury.

Oxalate nephrosis and renal sclerosis after renal transplantation in a cat

A 10-year-old castrated domestic shorthair cat received two renal allografts, 14 days apart, for the treatment of chronic renal failure. Oxalate nephrosis developed in both allografts, and they became nonfunctional. During the transplantation period, the cat was not exposed to exogenous sources of oxalate, and there was no evidence of primary type 2 hyperoxaluria before surgery. Urologic surgery, in particular renal transplantation, has been identified as a factor that can precipitate renal failure in human patients with decompensated renal function and hyperoxaluria. If hyperoxaluria was present before surgery in this cat, it was most likely caused by increased absorption or decreased metabolism of dietary oxalate.

Remnant kidney pathology after five-sixth nephrectomy in rat. I. A biochemical and morphological study

In Wistar male rats, hypertension was induced by 5/6 nephrectomy (5/6N). Body weight, blood pressure measurements, morphological and biochemical changes were followed (at four weekly intervals) for 12 weeks after 5/6N. Renal function was assessed by daily total urinary protein (TUP), plasma creatinine concentration [(Cr)p] and creatinine clearance rate. Plasma renin concentration (PRC), aldosterone concentration and erythrocyte content of sodium [Na]E and potassium [K]E were also investigated. Significant increases in systolic blood pressure (SBP), TUP, [(Cr)p] and [Na]E occurred after 4, 8, and 12 weeks of 5/6N. Progressive glomerulosclerosis (GSC), tubular atrophy and interstitial fibrosis were observed. Positive correlations were found between GSC and SBP and TUP. Positive correlations were also found between SBP and [Na]E and [(Cr)P]. PRC was not increased and showed no correlation with SBP. It is concluded that 5/6N produced hypertension associated with a series of morphological and biochemical alterations in kidney structure and function. In this model, mechanisms other than the renin-angiotensin system may be involved.

Intraglomerular pressure and mesangial stretching stimulate extracellular matrix formation in the rat

To define the interplay of glomerular hypertension and hypertrophy with mesangial extracellular matrix (ECM) deposition, we examined the effects of glomerular capillary distention and mesangial cell stretching on ECM synthesis. The volume of microdissected rat glomeruli (Vg), perfused ex vivo at increasing flows, was quantified and related to the proximal intraglomerular pressure (PIP). Glomerular compliance, expressed as the slope of the positive linear relationship between PIP and Vg was 7.68 x 10(3) microns 3/mmHg. Total Vg increment (PIP 0-150 mmHg) was 1.162 x 10(6) microns 3 or 61% (n = 13). A 16% increase in Vg was obtained over the PIP range equivalent to the pathophysiological limits of mean transcapillary pressure difference. A similar effect of renal perfusion on Vg was also noted histologically in tissue from kidneys perfused/fixed in vivo. Cultured mesangial cells undergoing cyclic stretching increased their synthesis of protein, total collagen, and key components of ECM (collagen IV, collagen I, laminin, fibronectin). Synthetic rates were stimulated by cell growth and the degree of stretching. These results suggest that capillary expansion and stretching of mesangial cells by glomerular hypertension provokes increased ECM production which is accentuated by cell growth and glomerular hypertrophy. Mesangial expansion and glomerulosclerosis might result from this interplay of mechanical and metabolic forces.

Adverse effect of the calcium channel blocker nitrendipine on nephrosclerosis in rats with renovascular hypertension

The effect of a 6-week treatment with the calcium channel blocker nitrendipine or the angiotensin converting enzyme inhibitor enalapril on blood pressure, albuminuria, renal hemodynamics, and morphology of the nonclipped kidney was studied in rats with two-kidney, one clip renovascular hypertension. Six weeks after clipping of one renal artery, hypertensive rats (178 +/- 4 mm Hg) were randomly assigned to three groups: untreated hypertensive controls (n = 8), enalapril-treated (n = 8), or nitrendipine-treated (n = 10). Sham-operated rats served as normotensive controls (128 +/- 3 mm Hg, n = 8). After 6 weeks of treatment, renal hemodynamics (glomerular filtration rate and renal plasma flow) were measured in the anesthetized rats. Renal tissue was obtained for determination of glomerular size and sclerosis. Enalapril but not nitrendipine reduced blood pressure significantly. After 6 weeks of therapy, glomerular filtration rate was not different among the studied groups. Renal plasma flow increased, but albumin excretion and glomerulosclerosis did not change after enalapril treatment. In contrast, in the nitrendipine-treated group albuminuria increased from 12.8 +/- 2 progressively to 163 +/- 55 compared with 19.2 +/- 9 mg/24 hr in the hypertensive controls. Furthermore, glomerulosclerosis index was significantly increased in the nitrendipine-treated group compared with the hypertensive controls (0.38 +/- 0.1 versus 0.13 +/- 0.04). In addition, glomerular size was higher in the nitrendipine-treated group (14.9 +/- 0.17 10(-3) mm2) but lower in the enalapril-treated group (11.5 +/- 0.15 10(-3) mm2) compared with the hypertensive controls (12.1 +/- 0.17 10(-3) mm2).(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced myogenic responsiveness of renal interlobular arteries in spontaneously hypertensive rats

We recently demonstrated that the interlobular artery (ILA) constricts in response to elevating renal arterial pressure (RAP), suggesting that the ILA contributes to renal autoregulation. In the present study, we examined the segmental myogenic responsiveness of the ILA in kidneys from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The tapered nature of the ILA allowed us to characterize the regional responsiveness, using the basal diameter to define segments as either proximal (greater than 60 microns), intermediate (40-60 microns), or distal (less than 40 microns). At 80 mm Hg, segmental diameters were similar in WKY and SHR arteries (proximal, 76.0 +/- 3.1 versus 71.6 +/- 3.5 microns; intermediate, 48.2 +/- 1.4 versus 48.1 +/- 1.7 microns; distal, 30.7 +/- 0.9 versus 27.9 +/- 1.3 microns for WKY and SHR, respectively). In both strains, intermediate and distal segments exhibited graded reductions in diameter as RAP was elevated, whereas proximal segments did not. Pressure-induced decrements in the diameters of distal ILA segments were similar in WKY (-24 +/- 2%) and SHR (-20 +/- 2%; p greater than 0.1). The intermediate ILA of SHR exhibited an augmented myogenic responsiveness, constricting at lower RAP levels and exhibiting greater maximal decrements in diameter at 180 mm Hg (i.e., -19 +/- 2% and -12 +/- 2% for SHR and WKY, respectively; p less than 0.05). Nifedipine (1.0 microM) reduced pressure-induced vasoconstriction of intermediate and distal ILA segments by 56 +/- 11% and 79 +/- 7%, respectively, in WKY.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal arteriolar diameters in spontaneously hypertensive rats. Vascular cast study

The relation between the arteriolar diameters and hypertensive glomerulosclerosis was studied by using microvascular casts and histological evaluation. Spontaneously hypertensive rats 4 weeks of age were divided into three groups: nontreated, captopril (40 mg/kg/day)-treated, and trichlormethiazide (1 mg/kg/day) with hydralazine (20 mg/kg/day)-treated. Wistar-Kyoto rats served as controls. At 6 weeks old, the captopril-treated rats showed a lower blood pressure and a larger afferent arteriolar diameter compared with the control rats. At 20 weeks old, the nontreated group exhibited hypertension and a lower arteriolar diameter ratio (afferent to efferent, 0.89 versus 1.22 in control group) because of afferent constriction and efferent dilatation, seen equally in the outer and inner cortexes. Glomerulosclerosis was accentuated only in the inner cortex of the nontreated group (score, 63 versus 29 in control group). In the two treated rat groups, the blood pressure was reduced and arteriolar diameter ratios were similar to those in the control group (1.18 and 1.26). The sclerosis score in the trichlormethiazide with hydralazine-treated rats (score, 26) was lower than in the nontreated rats but not the captopril-treated rats (score, 36). These results indicated that 1) in the hypertensive rats, despite a reduced diameter ratio, glomerulosclerosis was more severe in the inner cortex; 2) two therapies reduced blood pressure and reversed the arteriolar changes, but a decrease in glomerulosclerosis was seen only in the trichlormethiazide with hydralazine-treated rats; and 3) for development of glomerulosclerosis, factors other than hemodynamics may be important in addition to intraglomerular pressure.

Renal hemodynamics in normal and hypertensive pregnancy: lessons from micropuncture

Rats are an excellent animal model in which to study the changes in renal hemodynamics associated with normal pregnancy. Midterm pregnant rats exhibit a maximal renal vasodilation leading to increases in glomerular filtration rate (GFR) and renal plasma flow (RPF). Micropuncture studies in midterm pregnant Munich-Wistar rats have shown that single-nephron GFR (SNGFR) increases, due entirely to increases in plasma flow and, importantly, glomerular capillary blood pressure (PGC) remains unchanged in normotensive pregnancy, due to parallel and proportionally similar reductions in preglomerular (RA) and efferent (RE) arteriolar resistance. Despite the chronic gestational renal vasodilation, pregnancy in normotensive rats with either normal kidneys or a variety of underlying diseases, causes no adverse changes in renal function, perhaps because the glomeruli are protected from damaging high PGC. In the presence of systemic hypertension, the renal vasodilation of pregnancy could put the maternal kidney at risk of injury due to increases in PGC. There are few renal functional studies in preexisting, essential hypertension, but micropuncture studies in spontaneously hypertensive rats (SHRs) have shown that repetitive pregnancies in SHRs cause no functional impairment. Surprisingly, SHRs demonstrated no gestational renal vasodilation, although gestational decreases in peripheral resistance certainly occur in the SHR. This absence of gestational renal vasodilation may be a protective mechanism; it remains to be determined whether hypertensive states in which renal vasodilation does occur are associated with increased risk to the maternal kidney.

Absence of glomerular injury or nephron loss in a normotensive rat remnant kidney model

Severe reduction in renal mass (greater than 50%) in the rat uniformly results in progressive glomerular injury and loss of remnant nephrons postulated to be due to increases in glomerular function (hyperfiltration) and/or size (hypertrophy). Reduction in renal mass in the rat also leads to the development of systemic and/or glomerular hypertension. To examine the independent contributions of systemic hypertension and glomerular hyperfiltration and/or hypertrophy to progressive glomerular injury, a normotensive rat remnant kidney model was developed in the Wistar-Kyoto (WKY) strain. Of the 34 WKY rats that underwent 5/6 nephrectomy, 25 remained normotensive and without evidence of morphologic glomerular injury and/or nephron loss for up to 14 to 16 weeks, despite glomerular hyperfiltration and hypertrophy comparable to that previously observed in other rat strains. Micropuncture studies at approximately six weeks after reduction in renal mass demonstrated markedly increased SNGFR in remnant nephrons of normotensive rats as compared to controls (66 +/- 7 vs. 25 +/- 4 nl/min, P less than 0.01), but glomerular capillary pressures (PGC) estimated from stop flow pressures were only slightly increased (52.7 +/- 1 vs. 47.3 +/- 1 mm Hg, P less than 0.01). These data indicate that compensatory glomerular hyperfiltration and hypertrophy after 5/6 nephrectomy may not lead to progressive glomerular injury provided hypertension does not develop. These data further suggest that in the absence of systemic hypertension, increases in PGC required for adaptive hyperfiltration, may not be sufficient to initiate progressive glomerular injury and nephron loss.