Enalapril and renal injury in spontaneously hypertensive rats

Comparative proteomic analysis of renal tissue of normotensive and hypertensive rats

Comparative proteomic analysis of kidney tissue from normotensive (WKY) and spontaneously hypertensive (SHR) rats revealed quantitative and qualitative changes in renal proteins. The number of renal proteins specific for WKY rats (blood pressure 110-120 mm Hg) was 13-16. There were 20-24 renal proteins specific for SHR (blood pressure 180 mm Hg and more). The total number of identified renal proteins common for both rat strains included 972-975 proteins. A pairwise comparison of all possible (SHR-WKY) variants identified 8 proteins specific only for normotensive (WKY) animals, and 7 proteins specific only for hypertensive ones (SHR). Taking into consideration their biological roles, the lack of some enzyme proteins in hypertensive rats (for example, biliverdin reductase A) reduces the production of molecules exhibiting antihypertensive properties, while the appearance of others (e.g. betaine-homocysteine S-methyltransferase 2, septin 2, etc.) can be interpreted as a compensatory reaction. Renal proteins with altered relative content (with more than 2.5-fold change) accounted for no more than 5% of all identified proteins. Among the proteins with an increased relative content in hypertensive animals, the largest group consisted of proteins involved in the processes of energy generation and carbohydrate metabolism, as well as antioxidant and protective proteins. In the context of the development of hypertension, the identified relative changes can apparently be considered compensatory. Among the proteins with the most pronounced decrease in the relative content in hypertensive rats, the dramatic reduction in acyl-CoA medium-chain synthetase-3 (ACSM3) appears to make an important contribution to the development of renal pathology in these animals.

Hypertension alters the function and expression profile of the peptide cotransporters PEPT1 and PEPT2 in the rodent renal proximal tubule

Hypertension is a major risk factor for kidney and cardiovascular disease. The treatment of hypertensive individuals by selected ACE inhibitors and certain di-and tripeptides halts the progression of renal deterioration and extends life-span. Renal reabsorption of these low molecular weight substrates are mediated by the PEPT1 and PEPT2 cotransporters. This study aims to investigate whether hypertension and ageing affects renal PEPT cotransporters at gene, protein expression and distribution as well as function in the superficial cortex and the outer medulla of the kidney. Membrane vesicles from the brush border (BBMV) and outer medulla (OMMV) were isolated from the kidneys of young Wistar Kyoto (Y-WKY), young spontaneously hypertensive (Y-SHR), and middle aged SHR (M-SHR) rats. Transport activity was measured using the substrate, β-Ala-Lys (AMCA). Gene expression levels of PEPT genes were assessed with qRT-PCR while renal localisation of PEPT cotransporters was examined by immunohistochemistry with Western Blot validation. The K_m and V_max of renal PEPT1 were decreased significantly in SHR compared to WKY BBMV, whilst the Vmax of PEPT2 showed differences between SHR and WKY. By contrast to the reported cortical distribution of PEPT1, PEPT1-staining was detected in the outer medulla, whilst PEPT2 was expressed primarily in the cortex of all SHR; PEPT1 was significantly upregulated in the cortex of Y-SHR. These outcomes are indicative of a redistribution of PEPT1 and PEPT2 in the kidney proximal tubule under hypertensive conditions that has potential repercussions for nutrient handling and the therapeutic use of ACE inhibitors in hypertensive individuals.

Innovative lipid-based carriers containing cationic derivatives of polyisoprenoid alcohols augment the antihypertensive effectiveness of candesartan in spontaneously hypertensive rats

Novel lipid-based carriers, composed of cationic derivatives of polyisoprenoid alcohols (amino-prenols, APrens) and 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE), were designed. The carriers, which were previously shown to be nontoxic to living organisms, were now tested if suitable for administration of candesartan, an antihypertensive drug. Spontaneously hypertensive rats (SHR) received injections of candesartan (0.1 mg/kg body weight per day; s.c.) in freshly prepared carriers for two weeks. The rats' arterial pressure was measured by telemetry. Urine and blood collection were performed in metabolic cages. In a separate group of SHR, the pharmacokinetics of the new formulation was evaluated after a single subcutaneous injection. The antihypertensive activity of candesartan administered in DOPE dispersions containing APrens was distinctly greater than that of candesartan dispersions composed of DOPE only or administered in the classic solvent (sodium carbonate). The pharmacokinetic parameters clearly demonstrated that candesartan in APren carriers reached the bloodstream more rapidly and in much greater concentration (almost throughout the whole observation) than the same drug administered in dispersions of DOPE only or in solvent. Serum creatinine (P_Cr) decreased significantly only in the group receiving candesartan in carriers with APrens (from 0.80 ± 0.04 to 0.66 ± 0.09 mg/dl; p < 0.05), whereas in the other groups P_Cr remained at the same level after treatment. Moreover, the new derivatives increased the loading capacity of the carriers, which is a valuable feature for any drug delivery system. Taken together, our findings led us to conclude that APrens are potentially valuable components of lipid-based drug carriers.

Inhibition of PARP activation by enalapril is crucial for its renoprotective effect in cisplatin-induced nephrotoxicity in rats

Oxidative stress-induced PARP activation has been recognized to be a main factor in the pathogenesis of cisplatin-induced nephrotoxicity. Accumulating literature has revealed that ACE inhibitors may exert beneficial effect in several disease models via preventing PARP activation. Based on this hypothesis, we have evaluated the renoprotective effect of enalapril, an ACE inhibitor, and its underlying mechanism(s) in cisplatin-induced renal injury in rats. Male Albino Wistar rats were orally administered normal saline or enalapril (10, 20 and 40 mg/kg) for 10 days. Nephrotoxicity was induced by a single dose of cisplatin (8 mg/kg; i.p.) on the 7th day. The animals were thereafter sacrificed on the 11th day and both the kidneys were excised and processed for biochemical, histopathological, molecular, and immunohistochemical studies. Enalapril (40 mg/kg) significantly prevented cisplatin-induced renal dysfunction. In comparison to cisplatin-treated group, the elevation of BUN and creatinine levels was significantly less in this group. This improvement in kidney injury markers was well substantiated with reduced PARP expression along with phosphorylation of MAPKs including JNK/ERK/p38. Enalapril, in a dose-dependent fashion, attenuated cisplatin-induced oxidative stress as evidenced by augmented GSH, SOD and catalase activities, reduced TBARS and oxidative DNA damage (8-OHDG), and Nox-4 protein expression. Moreover, enalapril dose dependently inhibited cisplatin-induced inflammation (NF-κB/IKK-β/IL-6/Cox-2/TNF-α expressions), apoptosis (increased Bcl-2 and reduced p53, cytochrome c, Bax and caspase-3 expressions, and TUNEL/DAPI positivity) and preserved the structural integrity of the kidney. Thus, enalapril attenuated cisplatin-induced renal injury via inhibiting PARP activation and subsequent MAPKs/TNF-α/NF-κB mediated inflammatory and apoptotic response.

The effect of multivitamin-multimineral supplementation on the health status of inbred Wistar and spontaneously hypertensive rat strains

The nutraceutical industry has proliferated in recent years, with the most popular form of supplementation being the multivitamin-multimineral (MVMM) supplement. In the animal health sector, supplement use has also expanded. The objective of this study was to determine the effects of MVMM supplementation, beneficial or otherwise, on the general health status of the spontaneously hypertensive rat (SHR) strain, an animal model used in hypertension research. A commercially prepared MVMM supplement was given tri-weekly via oral dosing for 8 weeks to two groups of seven adult female SHR and Wistar rats. Their corresponding control groups were dosed with deionised water only. Systolic and diastolic blood pressure, fasting blood glucose, growth rate and food and water intake were measured weekly. At the end of 8 weeks, the animals were euthanased and a full blood profile, urine sodium to potassium ratio, blood urea nitrogen levels and total plasma cholesterol was measured for all groups. The results indicated that growth rate was higher for the SHR supplemented group. Supplementation also decreased diastolic blood pressure in both Wistar and SHR groups and increased red blood cell count and decreased total cholesterol in the SHR group. No adverse effects on the general health status of the animals were observed. MVMM supplementation may therefore be useful in aiding growth and delaying the onset of hypertension and its effects. It may also assist in the longevity of the breeding stock of SHR rats.

The giraffe kidney tolerates high arterial blood pressure by high renal interstitial pressure and low glomerular filtration rate

BACKGROUND

The tallest animal on earth, the giraffe (Giraffa camelopardalis) is endowed with a mean arterial blood pressure (MAP) twice that of other mammals. The kidneys reside at heart level and show no sign of hypertension-related damage. We hypothesized that a species-specific evolutionary adaption in the giraffe kidney allows normal for size renal haemodynamics and glomerular filtration rate (GFR) despite a MAP double that of other mammals.

METHODS

Fourteen anaesthetized giraffes were instrumented with vascular and bladder catheters to measure glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). Renal interstitial hydrostatic pressure (RIHP) was assessed by inserting a needle into the medullary parenchyma. Doppler ultrasound measurements provided renal artery resistive index (RI). Hormone concentrations as well as biomechanical, structural and histological characteristics of vascular and renal tissues were determined.

RESULTS

GFR averaged 342 ± 99 mL min(-1) and ERPF 1252 ± 305 mL min(-1) . RIHP varied between 45 and 140 mmHg. Renal pelvic pressure was 39 ± 2 mmHg and renal venous pressure 32 ± 4 mmHg. A valve-like structure at the junction of the renal and vena cava generated a pressure drop of 12 ± 2 mmHg. RI was 0.27. The renal capsule was durable with a calculated burst pressure of 600 mmHg. Plasma renin and AngII were 2.6 ± 0.5 mIU L(-1) and 9.1 ± 1.5 pg mL(-1) respectively.

CONCLUSION

In giraffes, GFR, ERPF and RI appear much lower than expected based on body mass. A strong renal capsule supports a RIHP, which is >10-fold that of other mammals effectively reducing the net filtration pressure and protecting against the high MAP.

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.

Indapamide lowers blood pressure by increasing production of epoxyeicosatrienoic acids in the kidney

Diuretics are widely used in the treatment of hypertension, although the precise mechanisms remain unknown. Epoxyeicosatrienoic acids (EETs), cytochrome P450 (P450) epoxygenase metabolites of arachidonic acid, play critical roles in regulation of blood pressure. The present study was carried out to investigate whether EETs participate in the antihypertensive effect of thiazide diuretics [hydrochlorothiazide (HCTZ)] and thiazide-like diuretics (indapamide). Male spontaneously hypertensive rats (SHRs) were treated with indapamide or HCTZ for 8 weeks. Systolic blood pressure, measured via tail-cuff plethysmography and confirmed via intra-arterial measurements, was significantly decreased in indapamide- and HCTZ-treated SHRs compared with saline-treated SHRs. Indapamide increased kidney CYP2C23 expression, decreased soluble epoxide hydrolase expression, increased urinary and renovascular 11,12- and 14,15-EETs, and decreased production of 11,12- and 14,15-dihydroxyeicosatrienoic acids in SHRs. No effect on expression of CYP4A1 or CYP2J3, or on 20-hydroxyeicosatetraenoic acid production, was observed, suggesting indapamide specifically targets CYP2C23-derived EETs. Treatment of SHRs with HCTZ did not affect the levels of P450s or their metabolites. Increased cAMP activity and protein kinase A expression were observed in the renal microvessels of indapamide-treated SHRs. Indapamide ameliorated oxidative stress and inflammation in renal cortices by down-regulating the expression of p47phox, nuclear factor-κB, transforming growth factor-β1, and phosphorylated mitogen-activated protein kinase. Furthermore, the p47phox-lowering effect of indapamide in angiotensin II-treated rat mesangial cells was partially blocked by the presence of N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide (MS-PPOH) or CYP2C23 small interfering RNA. Together, these results indicate that the hypotensive effects of indapamide are mediated, at least in part, by the P450 epoxygenase system in SHRs, and provide novel insights into the blood pressure-lowering mechanisms of diuretics.

Cerebral aqueduct block attenuates cardio-renal injuries in post-DOCA-NaCl-hypertensive Dahl R rats

The systemic and/or local effects of the hydrocephalic brain were investigated in DOCA-NaCl-hypertensive Dahl R rats induced by 250 mg kg(-1) DOCA in silicone and 1% saline water. After a 1-week recovery with 0.3% NaCl chow and tap water, one group had the aqueduct of Sylvius blocked with silicone and epoxy materials with a control sham group matching mean blood pressure (BP) and body weight. The 4-week-postsurgery BP on the 0.3% NaCl diet averaged 161±3.2 in the sham group and 146±2.3 mm Hg in the blocked group (P<0.0001). Both groups were then given an 8% NaCl diet and after 4 weeks, the sham group's BP was increased further with markedly increased mortality: 186 mm Hg vs. 154 mm Hg (P<0.0001); 12 sham rats died after 11 weeks, while all the blocked rats survived (P<0.0001). A transient change in plasma Na levels was observed in the blocked group after 48 h on the 8% NaCl diet. At 14 weeks, 0 sham rats survived, compared with 10 out of 16 blocked rats (P<0.0001). After 11 weeks on 8% NaCl, the average tail venous pressure in the sham group was significantly higher than that of the blocked rats (P<0.0001) indicating the end stage of renal and heart failure. The hearts and kidneys weighed significantly more in the sham vs. the blocked rats (P<0.0001 for both groups). These results indicate that the aqueduct block prevents post-DOCA hypertension and cardio-renal injuries, suggesting that centralized third ventricular brain signaling has a role in salt-genetic hypertension.

Programmed hypertension in rats treated with a NF-κB inhibitor during nephrogenesis: renal mechanisms

Suppression of the renin-angiotensin system (RAS) during murine lactation causes progressive renal injury, indicating a physiological action of angiotensin II on nephrogenesis. The nuclear factor NF-κB system is one of the main intracellular mediators of angiotensin II. We investigated whether inhibition of this system with pyrrolidine dithiocarbamate (PDTC) during rat nephrogenesis would lead to similar hypertension and renal injury as observed with RAS suppressors. Immediately after delivery, 32 Munich-Wistar dams, each nursing 6 male pups, were divided into 2 groups: C, untreated, and PDTC, receiving PDTC, 280 mg kg(-1) day(-1) orally, during 21 days. After weaning, the offspring were followed until 10 months of age without treatment. Adult rats that received neonatal PDTC exhibited stable hypertension and myocardial injury, without albuminuria. To gain additional insight into this process, the renal expression of RAS components and sodium transporters were determined by quantitative real-time PCR (qRT-PCR) at 3 and 10 months of life. Renal renin and angiotensinogen were upregulated at 3 and downregulated at 10 months of age, suggesting a role for early local RAS activation. Likewise, there was early upregulation of the proximal sodium/glucose and sodium/bicarbonate transporters, which abated later in life, suggesting that additional factors sustained hypertension in the long run. The conclusions drawn from the findings were as follows: (1) an intact NF-κB system during nephrogenesis may be essential to normal renal and cardiovascular function in adult life; (2) neonatal PDTC represents a new model of hypertension, lacking overt structural injury or functional impairment of the kidneys; and (3) hypertension in this model seems associated with early temporary activation of renal RAS and sodium transporters.

Gene expression profiling of cultured cells from brainstem of newborn spontaneously hypertensive and Wistar Kyoto rats

The spontaneously hypertensive rat (SHR) is a good model to study several diseases such as the attention-deficit hyperactivity disorder, cardiopulmonary impairment, nephropathy, as well as hypertension, which is a multifactor disease that possibly involves alterations in gene expression in hypertensive relative to normotensive subjects. In this study, we used high-density oligoarrays to compare gene expression profiles in cultured neurons and glia from brainstem of newborn normotensive Wistar Kyoto (WKY) and SHR rats. We found 376 genes differentially expressed between SHR and WKY brainstem cells that preferentially map to 17 metabolic/signaling pathways. Some of the pathways and regulated genes identified herein are obviously related to cardiovascular regulation; in addition there are several genes differentially expressed in SHR not yet associated to hypertension, which may be attributed to other differences between SHR and WKY strains. This constitute a rich resource for the identification and characterization of novel genes associated to phenotypic differences observed in SHR relative to WKY, including hypertension. In conclusion, this study describes for the first time the gene profiling pattern of brainstem cells from SHR and WKY rats, which opens up new possibilities and strategies of investigation and possible therapeutics to hypertension, as well as for the understanding of the brain contribution to phenotypic differences between SHR and WKY rats.

Effect of angiotensin II on glomerular structure in streptozotocin-induced diabetic rats

BACKGROUND/AIMS

The streptozotocin (STZ)-induced diabetic rat is a widely used animal model of human diabetic nephropathy. In this model, diabetic nephropathy progresses without significant elevation in blood pressure. Therefore, studies have examined the effect of hypertension in STZ spontaneously hypertensive rats (SHR). This study investigated angiotensin II (Ang II)-induced hypertension in diabetic nephropathy in the STZ-diabetic rat independent of deleterious genetic effects in SHR.

METHODS

Animals were divided as follows: nondiabetic controls (ND; n = 18); diabetic (STZ: 65 mg/kg; n = 16); Ang II-induced hypertensive ND (Ang II: 120 ng/kg/min; n = 9), and hypertensive diabetic rats (n = 18). Systolic blood pressure was measured by the tail-cuff method prior to STZ injection and then weekly. After 3 months, plasma creatinine, and 24-hour urine albumin and creatinine were measured and kidneys harvested for morphometry.

RESULTS

Ang II infusion increased systolic blood pressure in diabetic and ND rats. When combined with diabetes, Ang II increased albumin excretion rate (14-fold, p < 0.05), plasma creatinine (1.5-fold, p < 0.005) worsened creatinine clearance (37%, p < 0.002) and increased glomerular basement membrane width (1.2-fold, p < 0.0001).

CONCLUSION

Ang II caused moderate hypertension and accelerated diabetic nephropathy and glomerular structural changes. The Ang II-infused STZ-diabetic rat is an excellent model to study the deleterious glomerular effects of hypertension on diabetes independent of genetic traits.

Effects of aging and AT-1 receptor blockade on NO synthase expression and renal function in SHR

In an earlier study, we found increased NO production and NO synthase (NOS) expression in renal and vascular tissues of prehypertensive and adult spontaneously hypertensive rats (SHR). This study was designed to determine the effects of aging and AT-1 receptor blockade (losartan 30 mg/kg/day beginning at 8 weeks of age) on NO system in this model. Compared to the Wistar Kyoto (WKY) control rats, untreated SHR showed severe hypertension, elevated urinary NO metabolite (NO(chi)) excretion, marked upregulations of renal and vascular eNOS and iNOS proteins, normal renal function and heart weight at 9 weeks of age. Hypertension control with either AT-1 receptor or calcium channel blockade (felodipine 5 mg/kg/day) mitigated upregulation of NOS isoforms in the young SHR. With advanced age (63 weeks), the untreated SHR showed increased proteinuria, renal insufficiency, cardiomegaly, reduced urinary NO(chi) excretion and depressed renal and vascular NOS protein expressions as compared to the corresponding WKY group. AT-1 receptor blockade prevented proteinuria, renal insufficiency, cardiomegaly, and renal and vascular NOS deficiency. Thus, in young SHR, hypertension results in compensatory upregulation of renal and vascular NOS, which can be attenuated by vigorous antihypertensive therapy. With advanced age, untreated SHR exhibit cardiomegaly, renal dysfunction and marked reductions of eNOS and iNOS compared with the aged WKY rats. Hypertension control with AT-1 receptor blockade initiated early in the course of the disease prevents target organ damage and preserves renal and vascular NOS.

Association of renal injury with nitric oxide deficiency in aged SHR: prevention by hypertension control with AT1 blockade

BACKGROUND

Aged spontaneously hypertensive rats (SHR) develop end-stage renal disease resembling that of uncontrolled essential hypertension in humans. Nitric oxide (NO) and angiotensin II (Ang II) play an important role in the regulation of blood pressure and the growth of vascular smooth muscle and renal mesangial cells. The relationship between renal NO system, Ang II activity and renal injury in aged SHR is not fully understood.

METHODS

The 8-week-old SHR were randomized into losartan-treated (30 mg/kg/day for 55 weeks) and vehicle treated groups. The age-matched Wistar-Kyoto rats (WKY) served as controls. Renal histology and tissue expressions of endothelial and inducible NO synthases (eNOS and iNOS) and nitrotyrosine were examined at 63-weeks of age.

RESULTS

Compared to the WKY group, untreated SHR showed severe hypertension, proteinuria, renal insufficiency, a twofold decrease in renal tissue eNOS and iNOS expressions and massive nitrotyrosine accumulation. This was associated with severe glomerulosclerosis, tubular atrophy and interstitial fibrosis. Losartan therapy normalized blood pressure, prevented proteinuria and renal insufficiency, abrogated the fall in renal eNOS and iNOS protein contents, mitigated renal nitrotyrosine accumulation, and prevented the histological abnormalities found in the untreated SHR.

CONCLUSIONS

Aged SHR exhibit severe renal lesions with acquired NO deficiency that are prevented by hypertension control with AT1 blockade. These findings point to the possible role of NO deficiency in the pathogenesis of renal lesions in aged SHR.

Renal effects of efonidipine hydrochloride, a new calcium antagonist, in spontaneously hypertensive rats with glomerular injury

1. To obtain some insight into the renoprotective mechanism of the new calcium antagonist efonidipine hydrochloride, we evaluated the acute effects of efonidipine on proteinuria, glomerular haemodynamics and the tubuloglomerular feedback (TGF) mechanism in anaesthetized 24-25-week-old spontaneously hypertensive rats (SHR) with glomerular injury. 2. Efonidipine infusion at 10 micrograms/kg per h following a bolus dose of 10 micrograms/kg, i.v., reduced systemic blood pressure (BP) and renal vascular resistance, whereas renal plasma flow (RPF), glomerular filtration rate (GFR), filtration fraction, urine volume and urinary sodium excretion were unaltered. Urinary protein excretion was clearly diminished from 163 +/- 25 to 105 +/- 24 ng/min per g kidney weight. 3. Micropuncture experiments revealed that the maximal reduction of proximal stop-flow pressure (SFP), an index of glomerular capillary pressure (Pgc), induced by loop of Henle perfusion was significantly less with efonidipine treatment (6.7 +/- 1.0% of SFP with no loop flow) than in control (23.8 +/- 3.1%). In the presence of efonidipine, SFP at half-maximal reduction (SFP1/2max), which approximates Pgc at the in vivo steady state tubular flow rate, remained unchanged compared with control (36.9 +/- 0.8 vs 35.3 +/- 0.7 mmHg, respectively) and the slope of dependency on mean BP was not different between control and efonidipine. 4. These results indicate that efonidipine attenuates the TGF response in SHR by dilating the afferent arteriole, thus maintaining the level of RPF and GFR despite reduced renal perfusion pressure. Constant GFR and SFP1/2max under efonidipine suggest that single nephron GFR and Pgc remain unaltered and that a marked reduction in proteinuria is achieved without changes in single nephron GFR or Pgc of superficial nephrons.

Nephroprotection by long-term ACE inhibition with ramipril in spontaneously hypertensive stroke prone rats

BACKGROUND

The effect of life-long treatment with the ACE inhibitor ramipril on hypertension-induced histological changes in the kidney was tested in stroke-prone spontaneously hypertensive rats (SHR-SP).

METHODS

One-month-old pre-hypertensive SHR-SP were randomized into three groups of 45 animals each, and exposed via drinking water for their lifetime to a dose of: 1 mg.kg-1.d-1 ramipril (antihypertensive dose, HRA); 10 micrograms.kg-1.d-1 slight dose of ramipril (non-antihypertensive dose, LRA); or placebo. Histological and biochemical assessments were conducted after 15 months in ten rats each, when about 80% of the placebo group had died.

RESULTS

Kidneys from placebo treated SHR-SP showed pronounced arterial wall hypertrophy and sclerosis, arterial fibrinoid necrosis, glomerulopathy and tubular interstitial injury that were, in concert with normalized blood pressure, completely prevented by HRA treatment. LRA treatment did not affect any blood pressure increase, and also attenuated the development of arterial wall hypertrophy, sclerosis and arterial fibrinoid necrosis, though to a minor extent only, but did not change glomerular and tubulointerstitial degeneration. These effects of ramipril were associated with a dose-dependent inhibition of plasma and renal tissue ACE activities as well as lower serum concentrations of creatinine, but there were no changes in serum potassium.

CONCLUSIONS

Life-long HRA-induced ACE inhibition protects against hypertension-induced renal damages in SHR-SP. This is associated with a doubling of the lifespan in these animals.

Downregulation of the Klotho gene in the kidney under sustained circulatory stress in rats

We recently reported the isolation of the klotho gene, which in predominantly expressed in the kidney and involved in human aging phenotypes. In our previous studies, we demonstrated that the Klotho protein or its metabolites may possibly function as humoral factor(s) and protect against endothelial dysfunction because acetylcholine-mediated NO production in arteries was impaired in heterozygous klotho deficient mice (kl/+). However, the pathophysiological significance of the Klotho protein has not been clarified yet. In the present study, we examined expression of the klotho gene in the kidney of the following rat models for human diseases: (1) spontaneously hypertensive rat, (2) deoxycorticosterone acetate-salt hypertensive rat, (3) 5/6 nephrectomized rat, (4) non-insulin-dependent diabetes mellitus rat (the Otsuka Long-Evans Tokushima Fatty rat), and (5) rat with acute myocardial infarction. The expression levels of klotho mRNA in the kidney in these models were significantly lower than controls except for MI rats. This is the first report showing the expression of the klotho gene in the kidney is regulated under sustained circulatory stress such as long-term hypertension, diabetes mellitus, and chronic renal failure.

The SHR as a small animal model for radiocontrast renal failure. Relation of nephrotoxicity to animal's age, gender, strain, and dose of radiocontrast

The male spontaneously hypertensive rat (SHR), as it ages, suffers many of the renal and cardiovascular complications that are recognized in humans as risk factors for radiocontrast (RC) agent induced renal failure (RF). Knowledge of this led us to test this strain of rats as a small animal model for RC-induced renal failure (RC-RF). Functional studies demonstrated a significant fall in GFR in the recovery period after RC administration. In addition, histopathologic evaluation of the kidneys was done in this study. Our results are based on assigning separate scale values to the histopathological evaluation of the (a) glomeruli, (b) tubules, (c) interstitium, and (d) arteries and arterioles of the kidneys. Saline (S) was administered to one group and the RC agent Hypaque-76 (diatrizoate meglumine sodium) to paired groups of 5-, 8-, 10-, 12-, and 14-month-old male SHR. The results indicated that younger animals (5 and 8 months old) were resistant to the nephrotoxic effects of the RC, but developed susceptibility at 10 months of age, when spontaneous renal pathology became manifest. Both spontaneous renal pathology and RC-induced renal damage (RC-RD) increased as the animals aged. In addition, when the administered dose of RC was repeated after a short interval of only 6 h, the degree of RC-RD increased greatly. In parallel control studies of the influence of gender and strain on the response to RC in 12-month-old rats, neither hypertensive female SHR nor male normotensive Wistar-Kyoto (WKY) rats demonstrated significant spontaneous renal pathology or the marked susceptibility to RC nephrotoxicity shown by their male SHR counterparts. This small animal model for RC-RD, the mature male SHR, has the distinct advantage that risk factors for RC-RD, similar to those characterized in humans for RC-RF, develop spontaneously without requiring any special treatment or surgical intervention.

Enalapril and renal function in hypertensive rats transgenic for mouse renin gene

We examined the effect of long-term enalapril treatment on renal function and histology in the monogenetically hypertensive TGR(mRen2)27 rat strain. Untreated transgenic rats had significantly (P<.01) higher blood pressures than treated transgenic and control animals throughout the study. Urinary nitric oxide metabolite excretion was significantly lower in young transgenic rats and rose with enalapril, suggesting abnormal TGR nitric oxide production and its correction by enalapril. Converting enzyme inhibition produced preferential preglomerular vasodilatation and increased renal blood flow (6.5 +/- 0.5 versus 9.0 +/- 0.7 mL/min per gram kidney weight, P<.05) without altering whole-kidney and single-nephron glomerular filtration rates in TGR(mRen2)27. Glomerular capillary pressure fell modestly in treated transgenic animals (54 +/- 1 versus 50 +/- 1 mm Hg, P<.05). These hemodynamic changes were associated with reductions in albuminuria (59 +/- 6 versus 9 +/- 2 mg/d, P<.01) and glomerulosclerosis in TGR. However, urinary albumin excretion (15 +/- 3 versus 3 +/- 1 mg/d, P<.05) and glomerulosclerosis also declined in treated control animals in the absence of significant alterations in glomerular hemodynamics. The mechanism of the beneficial effect of enalapril on the TGR(mRen2)27 kidney is unclear but could involve either control of hypertension or suppression of the intrarenal renin-angiotensin system.

Endothelin-1 upregulation in the kidney of uninephrectomized spontaneously hypertensive rats and its modification by the angiotensin-converting enzyme inhibitor quinapril

Endothelin (ET-1) is a potent vasoconstrictor that plays an important role in the control of renal circulation and tubular function. The contribution of this peptide to the pathogenesis of systemic hypertension and renal failure remains largely undefined. In spontaneously hypertensive rats (SHR) uninephrectomized at 20 weeks of age (UNX-SHR) and followed until 45 weeks of age, we determined ET-1 gene expression in renal tissue by reverse transcription-polymerase chain reaction and its localization by in situ hybridization in paraffin-embedded kidney sections. Age-matched SHR and normotensive Wistar-Kyoto (WKY) rats were chosen as controls. At the end of the follow-up, UNX-SHR had high systolic blood pressure, intense proteinuria, mesangial expansion, focal and segmental glomerular sclerosis, and tubulointerstitial lesions. In relation to WKY and SHR, UNX-SHR exhibited an increase in ET-1 gene expression in renal cortex and medulla. By in situ hybridization and immunoperoxidase staining, an overexpression of ET-1 gene and protein were seen in mesangial and glomerular epithelial cells and in some proximal tubules and vessels. Angiotensin-converting enzyme (ACE) activity was significantly increased in the renal brush border. Since in mesangial cells, angiotensin II induces ET-1 synthesis, a group of UNX-SHR received the ACE inhibitor quinapril from the time of UNX. These animals had a decrease in blood pressure, proteinuria, and serum and brush border ACE activity and in the expression and synthesis of ET-1 in all renal areas. On the whole, these data show that UNX-SHR have an upregulation of ET-1 gene and protein in several structures of the kidney compared with SHR and WKY rats. Quinapril diminished ACE activity and ET-1 expression and synthesis coincidentally with an improvement in proteinuria and morphological lesions. The beneficial effects of ACE inhibitors may be due to the diminution of both angiotensin II and ET-1 generation.

Arthus C. Corcoran Memorial Lecture. Influence of nitric oxide and angiotensin II on renal involvement in hypertension

Remarkable advances have been made with prolonged antihypertensive therapy in reversing cardiovascular morbidity and mortality. Deaths from stroke have been reduced by 70% and from coronary heart disease by 35%. In contrast, endstage renal disease resulting from hypertension continues to increase. The explanations for this seeming paradox remain unresolved even though experimental models have demonstrated that certain antihypertensive agents may have beneficial renal and intrarenal hemodynamic effects; but reversal of the intrarenal pathological lesions have not been shown to improve. This discussion summarizes recent studies from our laboratory in aged (73- and 85-week-old) spontaneously hypertensive rats (SHR) with naturally occurring end-stage renal disease and in a model of aged SHR employing nitric oxide inhibition in younger, adult (20-week-old) SHR. Our findings demonstrated that the systemic and whole renal hemodynamics, intrarenal glomerular dynamics, proteinuria, and renal pathological lesions can be prevented or reversed with angiotensin-converting enzyme inhibition therapy but not with hydrochlorothiazide (at similar levels of arterial pressure reduction). The implications and possible mechanisms involved in the development of both naturally occurring and nitric oxide-exacerbated SHR are multifactorial, involving the endothelial nitric oxide system and its interaction with angiotensin II (and possibly bradykinin) among other factors. Moreover, these pathophysiological cellular mechanisms may be shared by the aging process as well as in naturally occurring spontaneous hypertension in the rat and, perhaps, in humans with essential hypertension. Thus, antihypertensive therapy seems to be specific in its ability to prevent and even reverse the pathophysiological derangements of renal involvement in hypertension. Thus, prevention and reversal of end-stage renal disease do not seem to require greater reduction of arterial pressure than with other target-organ involvement. However, they do require specific inhibition of the arteriolar and glomerular lesions produced by the disease.

Dietary fish oil prevents the development of renal damage in salt-loaded stroke-prone spontaneously hypertensive rats

1. Stroke-prone spontaneously hypertensive rats (SHRSP) fed a high salt diet rapidly develop proteinuria, a marker of renal damage. We have recently shown that supplementing the diet of these rats with pure omega-3 fatty acids can inhibit the development of proteinuria. The aim of the present study was to examine the underlying renal pathology and to see whether a similar benefit could be obtained with fish oil or canola oil. 2. Diets containing sodium (2% by weight) and 5% fish oil, canola oil, olive oil or safflower oil (the latter two serving as controls) were fed to groups of eight young SHRSP and the development of hypertension and proteinuria was monitored. After 9 weeks, rats were killed and their kidneys were taken for histological examination and fatty acid analysis. Urinary protein was characterized electrophoretically. 3. Patterns of protein excretion were consistent with the appearance of pathological changes in both glomeruli and tubules. Fish oil inhibited the elevation of blood pressure, prevented the development of proteinuria and minimized histological lesions. However, in rats fed canola oil, hypertension and renal damage were equally severe as in rats fed olive or safflower oil. 4. The prevention of hypertensive renal damage by dietary fish oil may be attributable to the increased incorporation of long-chain omega-3 fatty acids in the kidney.

Mononuclear cells in salivary glands of normal and isoproterenol-treated rats

The purpose of this study was to analyse the phenotypical distribution of resident cells of the mononuclear phagocyte system in rat salivary glands, and to determine whether isoproterenol induces alterations in macrophage and lymphocyte surface-marker expression. Frozen sections of gland tissues were prepared from five normal rats, and from six rats treated with 20 mg/kg isoproterenol/day for 10 days. A panel of six monoclonal antibodies was used to identify membrane markers associated primarily with monocytes (ED1), mature tissue macrophages (ED2), lymphoid macrophages (ED3), MHC class II (Ia) antigens (OX6), CD5-positive T lymphocytes (OX19), and rat B lymphocytes (OX33). Double-labelling techniques were used to detect the coexpression of ED1/ED2 and OX6/ED2 mononuclear cell markers in the major salivary glands. ED2-positive macrophages were predominant in all three major glands, ranging from 96 cells/0.87 mm2 field in the parotid gland to 165 cells/0.87 mm2 in the submandibular. OX19-positive T lymphocytes were rarely observed in submandibular and parotid glands but represented a distinguishing feature of the sublingual. Moderate numbers of ED3-positive macrophages also were detected in sublingual tissues. In the submandibular and parotid glands, isoproterenol resulted in a decrease in ED2-positive cells, but ED2-positive macrophages increased in sublingual glands with isoproterenol. Isoproterenol resulted in a decrease in MHC class II antigen expression on submandibular and sublingual mononuclear cells but an induction of Ia antigen in the parotid gland. Double labelling revealed that isoproterenol induced coexpression of ED1/ED2 markers on mononuclear cells in the submandibular glands, but ED1/ED2-positive cells were absent from other glands. However, coexpression of MHC class II markers on ED2-positive cells in the sublingual and parotid glands of normal rats was frequently observed, with isoproterenol decreasing coexpression in the sublingual gland and increasing it in the parotid. B lymphocytes were not detected in any of the glands examined. These findings indicate that important differences exist in normal resident mononuclear cell subsets among the major salivary glands of the rat. The differential effects of isoproterenol on inflammatory cells may reflect important differences in local salivary gland immunoregulation. Although salivary gland inflammation induced by isoproterenol does not appear to result from immune mechanisms, the rich population of T lymphocytes and ED3-positive macrophages, and presence of MHC class II antigens, suggest that the sublingual gland may function as an immune organ and have a role in mucosal immunity.

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)

Renal protective effect of efonidipine hydrochloride (NZ-105), a new calcium antagonist, in spontaneously hypertensive rats

1. We investigated the renal protective effect of efonidipine hydrochloride (NZ-105) in spontaneously hypertensive rats (SHR). SHR were given a diet containing 0.075% NZ-105 from 8 weeks old for 20 weeks. 2. 24-hr urinary protein excretion in the control SHR (drug-free diet) increased with age (from 77.3 mg/kg/day at 8 weeks old to 385.4 mg/kg/day at 28 weeks old), while that in NZ-105-treated SHR was maintained at almost the same level as that in Wistar-Kyoto rats (WKY), matched control animals throughout the experimental period. 3. The histological changes of the kidney were examined by light microscopy at the end of the treatment period. In control SHR, swelling and hyalinization of glomeruli, dilatation of renal tubules containing hyaline casts and arteriolosclerosis were revealed. The long-term administration of NZ-105 markedly suppressed these changes. 4. The kidney weights and plasma creatinine concentration in control SHR were higher than those in WKY, while they were significantly reduced in NZ-105-treated SHR. The long-term administration of NZ-105 also suppressed the elevation of systolic blood pressure and the increases of plasma renin activity and aldosterone concentration. 5. These findings suggest that NZ-105 inhibits the development of proteinuria and progressive kidney damage in SHR and may become a useful antihypertensive drug with the renal protective effect.

Renal effects of rapamycin in the spontaneously hypertensive rat

The effects of rapamycin (RAPA), administered at therapeutic doses, were investigated in the spontaneously hypertensive rat (SHR). Additionally, the reversibility of RAPA's renal effects was investigated at a supratherapeutic dose. At doses that were active in preventing heart and kidney allograft rejection in the rat (0.01-0.08 mg/kg i.v.), RAPA had no effect on kidney function or rat body weight gain. At higher doses (0.8 mg/kg), RAPA produced significant changes in kidney function parameters and caused a loss in body weight. Histopathologic changes, including necrotizing vasculopathy and tubular atrophy, were noted at therapeutic doses. The effects of RAPA on kidney function were completely reversible after a 2-week washout period, though the histopathologic changes were still evident. These studies demonstrate that RAPA does not impair kidney function at therapeutic doses when administered for 2 weeks but does appear to accelerate the naturally occurring renal lesions of the SHR.

Combination treatment of enalapril with nitrendipine in rats with renovascular hypertension

We have recently shown that treatment with the calcium channel blocker nitrendipine may aggravate albuminuria and glomerular injury in rats with two-kidney, one clip renovascular hypertension if arterial blood pressure is not reduced. To test whether nitrendipine also exerts its adverse renal effects when normotension is achieved, we examined the effect of combined therapy with nitrendipine and the converting enzyme inhibitor enalapril on blood pressure, albuminuria, glomerular filtration rate, and morphology of the nonclipped kidney. Rats treated with enalapril alone or in combination with the diuretic hydrochlorothiazide or rats treated with nitrendipine alone served as controls. Therapy was started 6 weeks after clipping of one renal artery. Nitrendipine alone did not reduce blood pressure but significantly increased albuminuria, diuresis, glomerular filtration rate, and glomerular volume and injury compared with untreated hypertensive controls. Increase of glomerular filtration rate, diuresis, and albuminuria was reversible after withdrawal of nitrendipine. Treatment with enalapril alone decreased blood pressure significantly but not to normotensive levels and was without significant effect on albuminuria and glomerular morphology. The combination of nitrendipine and enalapril reduced blood pressure to normotensive levels and not only prevented the increase of glomerular volume, glomerular filtration rate, diuresis, and albuminuria caused by nitrendipine alone but furthermore improved glomerular injury and albuminuria to levels not significantly different from normotensive controls. Enalapril in combination with the diuretic had similar beneficial effects on blood pressure, albuminuria, and glomerular injury. These data demonstrate that the adverse effects of nitrendipine monotherapy on glomerular structure and function can be prevented by the combination of nitrendipine and enalapril when blood pressure is normalized.

The diagnostic dilemma of hypertensive nephrosclerosis: the nephrologist's view

The appearance of progressive renal disease in elderly patients with essential hypertension, sometimes irrespective of blood pressure control, is frequently related to the association of hypertension and atheromatous renal disease. This disease may lead to renal failure through a renal artery stenosis and/or chronic microembolization into the kidney. Nonsevere uncomplicated essential hypertension is constantly associated with renal vascular changes that are qualitatively indistinguishable from those related to aging. Notwithstanding the fairly constant presence of so-called benign hypertensive nephrosclerosis in patients with established hypertension, only a subset of these patients show progressive renal damage. Three mechanisms of progression may be at play: (1) a combination of ischemic and hypertensive glomerular mechanisms in some susceptible humans; (2) nonhemodynamic factors such as local immune mechanisms; or (3) the involvement of metabolic abnormalities which favor glomerulosclerosis.

Endogenous creatinine clearance in the rat: strain variation

The clearance of endogenous creatinine was examined in five strains of rats (Wistar, Wistar Kyoto, Spontaneously Hypertensive Rats, Biobreeding/Worcester diabetic prone and diabetic resistant rats). Creatinine clearance was compared with inulin clearance as the standard. Conditions for clearance measurements were also varied (anesthesia with constant infusion, overnight collection of urine, fed vs. unfed state, single-injection technique). The clearance of creatinine adequately reflects the glomerular filtration rate in three strains (Wistar, Wistar-Kyoto and the Spontaneously Hypertensive Rat). In the two strains of the Biobreeding/Worcester rat creatinine clearance is consistently lower than the inulin clearance. When creatinine clearance is measured from an overnight collection of urine with food withheld it is always lower than when food is present. This clearance should always be validated by comparison with inulin clearance measured simultaneously or under comparable conditions. The ease with which endogenous creatinine clearance can be measured makes it a reasonable method when large numbers of repeated determinations of glomerular filtration rate are required.

Phenotypic characterization of resident macrophages in submandibular salivary glands of normal and isoproterenol-treated rats

Macrophages exert a major effect in the stimulation of lymphocytes and the modulation of immunological responses. To determine the presence and phenotypic distribution of the resident cells of the mononuclear phagocyte system in submandibular glands, frozen sections were prepared from five normal rats, and from six rats treated with 20 mg/kg isoproterenol/day for 10 days. A panel of six monoclonal antibodies was used to identify membrane markers associated primarily with circulatory monocytes (ED1), mature tissue macrophages (ED2), lymphoid macrophages (ED3), Ia antigen (OX6), CD5-positive T lymphocytes (OX19) and rat B lymphocytes (OX33). Cells identified by each monoclonal antibody were quantified by averaging the number of positive cells in 10 consecutive random high-power fields. ED2 cells (165 cells/field) were predominant in normal rat submandibular gland, followed by lower numbers of OX6-positive cells (18 cells/field). Cells positive for the remaining markers were also present in smaller amounts. In submandibular glands, treatment of rats with isoproterenol resulted in an increase in ED1-positive cells (from 2 to 39 cells/field), but also in substantial decreases in the number of cells positive for the remaining cell markers. B cells were not detected in any of the submandibular glands examined. These data suggest that isoproterenol induces a mild inflammatory response within rat submandibular glands that is not observed in normal glands. This results in an increase in the relative number of infiltrating monocytes compared to the number of more mature tissue macrophages.

Pathogenesis of the essential hypertensions

The pathogenesis of essential hypertension (EH) is reviewed with a special focus on the development phase or the pre-hypertensive period. Three animal models are presented: the spontaneously hypertensive rat, the Dahl's salt-sensitive rat, and the Milan hypertensive rat. Some of the findings in animal models have inspired new fields and technical approaches for studying EH in man. From the original idea of Page, a new mosaic of various etiological parameters serves as a basis for reviewing the multiple facets of EH in man. One must conclude that EH is heterogeneous disease and most likely every single hypertensive patient belongs to a subgroup of the whole population of hypertensives.