Accelerated cell turnover 48 h after intestinal ischemia is NOTCH independent.

AIM OF THE STUDY: Notch signaling plays important roles in maintaining intestinal epithelial homeostasis. When Notch signaling is blocked, proliferation ceases and epithelial cells become secretory. The purpose of the present study was to evaluate the role of Notch signaling pathway following intestinal ischemia-reperfusion (IR) injury in a rat model. MATERIALS AND METHODS: Male Sprague-Dawley rats were randomly divided into four experimental groups: Sham-24 and Sham-48 rats underwent laparotomy and were killed 24 or 48 h later, respectively; IR-24 and IR-48 rats underwent occlusion of SMA and portal vein for 30 min followed by 24 or 48 h of reperfusion, respectively. Enterocyte proliferation and enterocyte apoptosis were determined at killing. Notch-related gene and protein expression were determined using Real Time PCR, Western blotting and immunohistochemistry 48 h followed IR. MAIN RESULTS: IR-48 rats demonstrated significantly increased rates of cell proliferation and increased cell apoptosis in both jejunum and ileum compared to Sham rats. IR-48 rats exhibited a significant decrease in Notch-1 protein expression (Western blot) that was coincided with a significant decrease in the number of Notch-1 positive cells (immunohistochemistry) in jejunum (35% decrease, p < 0.05) and ileum (twofold decrease, p < 0.05) as well as Hes-1 positive cells in jejunum (28% decrease, p < 0.05) and ileum (31% decrease, p < 0.05) compared to Sham-48 rats. CONCLUSIONS: Forty-eight hours following intestinal IR in rats, accelerated cell turnover was associated by inhibited Notch signaling pathway. Intestinal stem cells differentiation toward secretory progenitors rather than differentiation toward absorptive cells is important at this phase of intestinal recovery.

Cyclosporine A induces endothelin-converting enzyme-1: Studies in vivo and in vitro.

AIM: Cyclosporine A (CsA) induces renal vasoconstriction and hypoxia and enhances the expression of endothelin-1 (ET-1) pro-hormone (pre-pro-ET-1), plausibly leading to a feed-forward loop of renal vasoconstriction, hypoxia and enhanced synthesis of the potent vasoconstrictor ET-1. Endothelin-converting enzyme (ECE)-1 cleaves big endothelin to generate endothelin (ET)-1 and is upregulated by hypoxia via hypoxia-inducible factor (HIF). We hypothesized that in addition to the direct induction of ET-1 synthesis, CsA might also intensify renal ECE-1 expression, thus contributing to enhanced ET-1 synthesis following CsA. METHODS: CsA was administered to Sprague Dawley rats (120 mg/kg/SC) for 4 days, and renal HIF and ECE-1 expression were assessed with Western blots and immunostaining. Human umbilical vein endothelial cells (HUVEC) and proximal tubular cell line (HK-2) were subjected to CsA, and ECE-1 induction was evaluated using real-time mRNA PCR and Western blots. RESULTS: Cyclosporine A intensified renal parenchymal ECE-1 expression in the rat kidney, particularly in distal nephron segments, along with renal hypoxia (detected by pimonidazole adducts) and HIF expression, in line with our recent observations showing episodic hypoxia in mice subjected to CsA. Furthermore, in cultured normoxic HUVEC and HK-2 cells, CsA dose-dependently induced both pre-pro-ET-1 and ECE-1 mRNA and protein expression, with enhanced ET-1 generation. CONCLUSION: CsA induces ECE-1 via both hypoxic and non-hypoxic pathways. ECE-1 may contribute to increased renal ET-1 generation following CsA, participating in a feed-forward loop of renal parenchymal hypoxia and ET synthesis.

Ex vivo endothelin dependent contraction of the remodeled rat spiral artery.

INTRODUCTION: Similarities of the rat to the human placenta make rat pregnancy models relevant to the study of human gestational diseases. Understanding of species differences is necessary to extrapolate from animal models to humans. We observed alpha-smooth muscle actin (αSMA) expression in rat endovascular trophoblasts (EVasT) and investigated the spatial and temporal expression of smooth muscle (SM) proteins and their potential function in remodeled spiral artery. METHODS: Rat placentas were examined from gestational day 13 to term, and were immunostained for cytokeratin, αSMA, alpha heavy chain of SM myosin, non-muscle myosin, Rho proteins, regulators of SM gene expression, myocardin, an early marker of SM differentiation and endothelin receptors A and B (ETA, ETB). Transmission electron microscopy (TEM) was performed. Modified spiral artery rings were studied ex vivo for endothelin-1- induced contraction. RESULTS: EVasT expressed SM proteins co-localizing with cytokeratin confirming their trophoblastic origin from gestational day 13 to term. Thin fibers, consistent with actin fibers, were observed by TEM, in the cellular localization of αSMA in EVasT. Functional experiments revealed that addition of 10(-7) M endothelin-1 ex vivo reduced vascular lumen area by 11.1% ± 1.8% compared with control. This effect was reduced to only 1.0 ± 1.7% with ETA antagonist, and to 5.4 ± 1.7% contraction by ETB antagonist, p < 0.002, for all. DISCUSSION: The expression of SM proteins in EVasT along with the contractibility of the rat remodeled spiral artery ex vivo, suggest that some vascular tone is potentially maintained by endothelin-1, and may play a role in situations of dysregulation of the vasoactive systems.

Impulse conduction and gap junctional remodelling by endothelin-1 in cultured neonatal rat ventricular myocytes.

Endothelin-1 (ET-1) is an important contributor to ventricular hypertrophy and failure, which are associated with arrhythmogenesis and sudden death. To elucidate the mechanism(s) underlying the arrhythmogenic effects of ET-1 we tested the hypothesis that long-term (24 hrs) exposure to ET-1 impairs impulse conduction in cultures of neonatal rat ventricular myocytes (NRVM). NRVM were seeded on micro-electrode-arrays (MEAs, Multi Channel Systems, Reutlingen, Germany) and exposed to 50 nM ET-1 for 24 hrs. Hypertrophy was assessed by morphological and molecular methods. Consecutive recordings of paced activation times from the same cultures were conducted at baseline and after 3, 6 and 24 hrs, and activation maps for each time period constructed. Gap junctional Cx43 expression was assessed using Western blot and confocal microscopy of immunofluorescence staining using anti-Cx43 antibodies. ET-1 caused hypertrophy as indicated by a 70% increase in mRNA for atrial natriuretic peptide (P < 0.05), and increased cell areas (P < 0.05) compared to control. ET-1 also caused a time-dependent decrease in conduction velocity that was evident after 3 hrs of exposure to ET-1, and was augmented at 24 hrs, compared to controls (P < 0.01). ET-1 increased total Cx43 protein by approximately 40% (P < 0.05) without affecting non- phosphorylated Cx43 (NP-Cx43) protein expression. Quantitative confocal microscopy showed a approximately 30% decrease in the Cx43 immunofluorescence per field in the ET-1 group (P < 0.05) and a reduced field stain intensity (P < 0.05), compared to controls. ET-1-induced hypertrophy was accompanied by reduction in conduction velocity and gap junctional remodelling. The reduction in conduction velocity may play a role in ET-1 induced susceptibility to arrhythmogenesis.

Diabetes and radiocontrast media increase endothelin converting enzyme-1 in the kidney.

Plasma endothelin-1 levels rise in diabetes and after exposure to contrast media suggesting a role in progressive diabetic and acute radiocontrast nephropathies. Here we studied individual and combined effects of streptozotocin-induced diabetes and contrast media on renal endothelin converting enzyme-1 levels in the rat. In vivo, medullary (but not cortical) endothelin converting enzyme protein gradually increased 4 to 5-fold following the induction of diabetes or after the administration of contrast media but rose 15-fold when diabetic rats were given contrast media. Changes in mRNA expression paralleled those of the protein. Immunohistochemistry confirmed that increased tubular and endothelial cell endothelin converting enzyme-1 were most pronounced in the medulla. In vitro, endothelin-1 levels increased 3-fold following incubation of endothelial cells with media high in glucose or with contrast and 4-fold with their combination. Endothelin converting enzyme-1 protein and mRNA expression changed in a similar pattern while prepro endothelin-1 mRNA increased with each insult but not in an additive way. Our study shows that diabetes and contrast media up-regulate renal medullary endothelin converting enzyme-1 expression and synthesis.

Adaptation to hypoxia in the diabetic rat kidney.

Hypoxia of the kidney in diabetes could predispose it to develop acute and chronic renal failure. To examine the relationship between renal hypoxia and renal failure, we measured hypoxia (as a pimonidazole adducts), hypoxia-inducible factors (HIFs), and a hypoxia target gene heme oxygenase-1. The studies were performed in rats with streptozotocin (STZ)-induced diabetes, Cohen diabetes sensitive rats, and during short-term artificial hyperglycemia in rats induced by intravenous glucose and octreotide. STZ-treated rats received insulin, the superoxide dismutase mimetic tempol, or contrast medium. Radiocontrast media causes hypoxia and HIF induction. Hypoxia, HIFs, and heme oxygenase were undetectable in controls, but transiently activated in STZ-treated and the Cohen diabetes sensitive rats. Different patterns of HIFs and pimonidazole were observed between the three models. Insulin abolished pimonidazole and HIF induction, whereas tempol lead to increased HIFs and heme oxygenase induction at similar levels of pimonidazole. When compared with control rats, STZ-treated rats exhibited more intense and protracted renal pimonidazole, with augmented hypoxia inducible factor production and reduced GFR following contrast media. Our data suggest that both regional hypoxia and hypoxia adaptation transiently occur in early stages of experimental diabetes, largely dependent on hyperglycemia or after contrast media. Tempol may augment the HIF response in diabetes.

Effect of dietary sodium intake on the expression of endothelin-converting enzyme in the renal medulla.

BACKGROUND/AIM: Endothelin-converting enzyme (ECE) catalyzes the generation of endothelin-1 (ET-1) from its inactive precursor big-ET-1. Previous studies suggested that the ET-1 system is involved in the regulation of sodium excretion by the kidney. In particular, ET-1 via the ET(B) receptor-mediated signaling has been shown to increase renal medullary blood flow and decrease sodium transport in the collecting duct, both acting to promote renal sodium excretion. The present study was designed to evaluate the possibility that alterations in dietary salt intake may regulate the ECE-1. METHODS: Wistar rats were fed for 3 days either with a diet containing low salt (0.01% NaCl), normal salt (0.5% NaCl), or high salt intake, either by high salt diet (4% NaCl) or normal salt diet plus 0.9% saline drinking. The expression of and immunoreactive protein levels of ECE-1 in the renal medulla was studied by RT-PCR, Northern blotting and Western blotting techniques. RESULTS: The expression of ECE-1 mRNA (by RT-PCR and Northern blotting), as well as the immunoreactive levels of ECE-1, were significantly higher in the renal medulla of rats exposed to high salt intake than in rats on normal salt diet. CONCLUSION: The findings suggest that upregulation of ECE-1, leading to increased generation of ET-1 in the renal medulla, may be a compensatory mechanism promoting enhanced sodium excretion by the kidney in response to high salt intake.

Evaluation of atrial natriuretic peptide and brain natriuretic peptide in atrial granules of rats with experimental congestive heart failure.

The natriuretic peptides are believed to play an important role in the pathophysiology of congestive heart failure (CHF). We utilized a quantitative cytomorphometric method, using double immunocytochemical labeling, to assess the characteristics of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in atrial granules in an experimental model of rats with CHF induced by aortocaval fistula. Rats with CHF were further divided into decompensated (sodium-retaining) and compensated (sodium-excreting) subgroups and compared with a sham-operated control group. A total of 947 granules in myocytes in the right atrium were analyzed, using electron microscopy and a computerized analysis system. Decompensated CHF was associated with alterations in the modal nature of granule content packing, as depicted by moving bin analysis, and in the granule density of both peptides. In control rats, the mean density of gold particles attached to both peptides was 347.0 +/- 103.6 and 306.3 +/- 89.9 gold particles/microm2 for ANP and BNP, respectively. Similar mean density was revealed in the compensated rats (390.6 +/- 81.0 and 351.3 +/- 62.1 gold particles/microm2 for ANP and BNP, respectively). However, in rats with decompensated CHF, a significant decrease in the mean density of gold particles was observed (141.6 +/- 67.3 and 158.0 +/- 71.2 gold particles/microm2 for ANP and BNP, respectively; p<0.05 compared with compensated rats, for both ANP and BNP). The ANP:BNP ratio did not differ between groups. These findings indicate that the development of decompensated CHF in rats with aortocaval fistula is associated with a marked decrease in the density of both peptides in atrial granules, as well as in alterations in the quantal nature of granule formation. The data further suggest that both peptides, ANP and BNP, may be regulated in the atrium by a common secretory mechanism in CHF.

The intrarenal endothelin system and hypertension.

The kidney is both a source of endothelin (ET) generation and an important target organ of this peptide. The highest concentrations of ET-1 in the body exist in the renal medulla, where it mediates natriuretic and diuretic effects through the ET(B) receptor subtype. It is proposed that aberrations in the renal ET system may lead to sodium and water retention and subsequently to the development of hypertension.

Temporal changes in natriuretic and antinatriuretic systems after closure of a large arteriovenous fistula.

OBJECTIVE: Surgical closure of a large arteriovenous (A-V) fistula in patients and animals is associated with prompt diuresis and natriuresis. However, the mechanisms underlying these changes remained largely unknown. METHODS: The present study evaluated the hormonal balance between major antinatriuretic systems (plasma renin activity, PRA, and arginine vasopressin, AVP) and natriuretic systems (atrial natriuretic peptide, ANP, and renal nitric oxide, NO) in Wistar rats with an A-V fistula (1.2 mm O.D., side to side) between the abdominal aorta and inferior vena cava. RESULTS: The placement of an A-V fistula caused progressive sodium retention (UNaV decreased from 1500 to 100 microequiv./day), a significant drop in mean arterial blood pressure (MAP) from 127+/-3 to 75+/-2 mmHg (P<0.01), and a significant increase in ANP (from 94+/-12 to 389+/-135 pg/ml, P<0.05), PRA (from 22.1+/-2.0 to 47+/-14 ng angiotensin I [Ang I]/ml/h, P<0.05), AVP (from 14.2+/-3.6 to 37.7+/-9.6 pg/ml, P<0.05), norepinephrine (from 184.2+/-40.5 to 1112.6+/-293.2 pg/ml, P<0.05) and epinephrine (from 667.5+/-175.9 to 2049.8+/-496.9 pg/ml, P<0.05). Furthermore, these changes were associated with a 3-fold increase in the renal medullary immunoreactive levels of endothelial NO synthase (eNOS), an endogenous vasodilator that plays an important role in the regulation of medullary blood flow. After 6 days, rats with A-V fistula and maximal sodium retention underwent surgical closure of the A-V fistula. The A-V fistula closure was associated with dramatic natriuresis (UNaV=2563+/-78 and 1918+/-246 microEq/day on days 3 and 6 following the closure, respectively) and restoration of MAP to normal levels (111+/-6 mmHg); PRA decreased to 29+/-5 ng Ang I/ml/h, AVP to 20.3+/-7.1 pg/ml, and medullary eNOS declined to basal levels, whereas plasma ANP concentrations remained elevated (380+/-90 pg/ml) after 3 days and returned to normal (92+/-12 pg/ml) on day 6. CONCLUSIONS: These results demonstrate that the creation of A-V fistula is associated with activation of both natriuretic and antinatriuretic systems. Closure of A-V fistula is characterized by shifting the balance in favor of the natriuretic substances. Moreover, the observed alterations in medullary eNOS following the creation and closure of A-V fistula suggest that this system, an important determinant of medullary blood flow, may contribute significantly to the regulation of sodium excretion in this model.

Compensated heart failure predisposes to outer medullary tubular injury: studies in rats.

BACKGROUND: Heart failure (HF) is considered a putative factor predisposing to acute renal failure (ARF). Since outer medullary hypoxic injury may play an important role in the pathogenesis of acute tubular necrosis, we explored the impact of experimental HF on the propensity to develop ARF with hypoxic medullary injury following the inhibition of prostaglandin and nitric oxide synthesis. METHODS: Compensated, high-output HF was induced in Sprague-Dawley rats by aorto-caval fistula. At the eighth to ninth postoperative day, the rats were injected with indomethacin and N(omega) nitro-L-arginine methyl ester (L-NAME; ARF protocol) and were sacrificed 24 hours later for morphologic evaluation. RESULTS: Kidney function comparably declined in HF-ARF rats and in control sham operated animals (CTR-ARF). Nevertheless, outer medullary hypoxic damage with medullary thick ascending limb (mTAL) necrosis occurred almost exclusively in the HF-ARF group (11 +/- 4% vs. 0.2 +/- 0.2% of tubules in CTR-ARF, P < 0.03). In a third group of HF animals subjected to vehicles only (HF-Nil), kidney function was preserved and renal morphology remained intact. Papillary-tip necrosis was consistently found in all animals subjected to indomethacin and L-NAME, irrespective of preconditioning. Morphometric evaluation disclosed that HF was not associated with mTAL hypertrophy. CONCLUSIONS: Incipient HF predisposes to hypoxic outer medullary injury, probably reflecting the impact of regional vasoconstrictive stimuli rather than tubular hypertrophy when protective local vasodilating mechanisms are hampered. The presence and extent of outer medullary hypoxic damage cannot be predicted from the functional derangement, which in the experimental settings may also represent prerenal azotemia or papillary damage.

Intrarenal expression and distribution of cyclooxygenase isoforms in rats with experimental heart failure.

The generation of PGs from arachidonic acid is mediated by cyclooxygenase (COX), which consists of a constitutive (COX-1) and an inducible (COX-2) isoform. The present study evaluated the relative expression and immunoreactive levels of COX-1 and COX-2, by means of RT-PCR, Western blot analysis, and immunohistochemistry, in the renal cortex and medulla of rats with congestive heart failure (CHF), induced by the placement of an aortocaval fistula. In addition, we examined the effects of a COX-1 inhibitor (piroxicam), COX-2 inhibitor (nimesulide), and nonselective COX inhibitor (indomethacin) at a dose of 5 mg/kg, on intrarenal blood flow by laser Doppler flowmetry. COX-1 and COX-2 mRNAs were abundantly expressed in the renal medulla of control and CHF rats and only minimally in the cortex. Moreover, both RT-PCR (32-36 cycles) and Western blot techniques revealed upregulation of medullary COX-2, but not of COX-1, in rats with advanced heart failure. In line with these findings, all three tested COX inhibitors provoked significant and sustained decreases (Delta approximately -20%) in medullary blood flow (MBF), which were similar in magnitude and duration in control animals. However, in CHF rats, indomethacin produced a greater reduction in MBF than that obtained with either piroxicam or nimesulide. Taken together, these results indicate that 1) both COX-1 and COX-2 are predominantly expressed in the renal medulla and 2) experimental CHF is associated with selective overexpression of COX-2. The latter may represent a mechanism aimed at defending MBF in the face of a decrease in renal perfusion pressure during the development of CHF.

Bosentan and the endothelin system in congestive heart failure.

The endothelin system appears to play an important role in the pathophysiology of congestive heart failure (CHF). Endothelin receptor antagonists represent a novel class of agents that are being evaluated for their potential benefits in treating various cardiovascular disorders. Bosentan is an orally active endothelin receptor antagonist that has been studied for the treatment of CHF. Early clinical experience with bosentan has confirmed some benefits on hemodynamic parameters in patients with CHF. Its role in slowing the progression of the disease and improving survival remains to be elucidated.

Effects of A-192621.1, a specific endothelin-B antagonist, on intrarenal hemodynamic responses to endothelin-1.

The present study examined the effects of A-192621.1, a highly selective endothelin-B- (ETB) receptor antagonist, on the renal hemodynamic and systemic actions of endothelin-1 (ET-1). Intravenous injection of ET-1 (1.0 nmol/kg) into anesthetized rats produced a sustained decrease in renal blood flow (assessed by ultrasonic flowmeter) and a significant increase in renal vascular resistance, as well as an increase in mean arterial pressure. These changes were significantly augmented by pretreatment with A-192621.1 (3.0 mg/kg/h). Analysis of intrarenal blood flow by laser-Doppler flowmeter revealed that ET-1 caused a marked and sustained decrease in cortical blood flow, associated with a transient increase in medullary blood flow. The reduction in cortical blood flow in response to ET-1 was further enhanced by pretreatment with A-192621.1, whereas the ET-1-induced medullary vasodilatation was completely abolished and reversed into a vasoconstrictor response. These findings suggest that the ETB-receptors mediate the systemic and renal vasodilatory actions of ET-1 in the rat, and that their activation may serve as a physiological counterbalance that modulates ET-1-induced vasoconstriction.

Mechanisms of big endothelin-1-induced diuresis and natriuresis : role of ET(B) receptors.

Endothelin-1 (ET-1) at high concentrations has marked antidiuretic and antinatriuretic activities, whereas its precursor, big endothelin-1 (big ET-1), has surprisingly potent diuretic and natriuretic actions. The mechanisms underlying the excretory effects of big ET-1 have not been fully elucidated. To explore these mechanisms, we examined the effects of a highly selective ET(B) antagonist (A-192621.1), a calcium channel blocker (verapamil), a nitric oxide synthase inhibitor (N-nitro-L-arginine methyl ester [L-NAME]), and a cyclooxygenase inhibitor (indomethacin) on the systemic and renal actions of big ET-1 in anesthetized rats. An intravenous bolus injection of incremental doses of big ET-1 (0.3, 1. 0, and 3.0 nmol/kg) produced a significant hypertensive effect that was dose dependent and prolonged (from 113+/-7 mm Hg to a maximum of 148+/-6 mm Hg). The administration of big ET-1 induced marked diuretic and natriuretic responses (urinary flow rate increased from 8.5+/-1 to 110+/-14 microL/min, and fractional excretion of sodium increased from 0.38+/-0.13% to 7.51+/-1.24%). Glomerular filtration rate and renal plasma flow significantly decreased only at the highest dose of big ET-1. Pretreatment with A-192621.1 (3 mg/kg plus 3 mg. kg(-1). h(-1)) significantly abolished the diuretic (17+/-5 microL/min to a maximum of 19+/-3 microL/min) and natriuretic (0. 29+/-0.1% to a maximum of 1.93+/-0.37%) responses induced by big ET-1. Moreover, A-192621.1 potentiated the decline in glomerular filtration rate and renal plasma flow and the increase in mean arterial blood pressure produced by the low doses of big ET-1. Similar to A-192621.1, pretreatment with a nitric oxide synthase inhibitor (L-NAME, 10 mg/kg plus 5 mg. kg(-1). h(-1)) significantly and comparably reduced the diuretic and natriuretic actions of big ET-1 and augmented the hypoperfusion/hypofiltration and systemic vasoconstriction induced by high doses of the peptide. Pretreatment with verapamil (2 mg. kg(-1). h(-1)) slightly inhibited the diuretic/natriuretic effects of the high-dose big ET-1 and completely prevented the increase in mean arterial blood pressure provoked by the peptide. Unlike verapamil and L-NAME, only indomethacin administration was associated with significant natriuretic/diuretic responses and did not influence the pressor effect and renal actions of big ET-1. Taken together, these results suggest that big ET-1-induced diuretic and natriuretic responses are mediated mainly by stimulation of nitric oxide production coupled to ET(B) receptor subtype activation.

Acute renal failure complicating muscle crush injury.

Extensive skeletal muscle injury, whether caused by mechanical crush or by extreme physical exertion, is incompatible with life, unless treated early and vigorously. The immediate cause of morbidity is leakiness of the sarcolemmal membrane to cardiotoxic or nephrotoxic cations and metabolites (K, PO4, myoglobin and urate) of the sarcoplasma, and rapid massive uptake by the muscles of extracellular fluid, sodium and calcium, leading to profound hypovolemic and hyocalcemic shock. Casualties who survive the early steep of hyperkalemia and arterial hypotension are susceptible to myoglubinuric acute renal failure owing mainly to the combination of renal vasoconstriction, nephrotoxicity, and tubular obstruction by myoglobin plugs and urate. Management includes immediate (prehospital) intravenous volume replacement followed by mannitol-alkaline diuresis. The alkali regimen ameliorates the acidosis associated with shock and the hyperkalemia, and protects against the nephrotoxicity of myoglobin and urate by alkalinization of the urine. Mannitol, through its impermeant hyperoncotic properties, decompresses and mobilizes muscle edema and promotes renal tubular flow, thus flushing myoglobin plugs and enhancing urinary elimination of nephrotoxic metabolites. With this regimen and when necessary also with the use of dialysis, a substantial salvage of lives, limbs, and kidney function has been achieved recently compared with invariable mortality for casualties who were buried for 3 to 4 hours or more in the early 1940s (World War 2).

Effects of eprosartan on renal function and cardiac hypertrophy in rats with experimental heart failure.

Activation of the renin-angiotensin system may contribute to the derangement in renal and cardiac function in congestive heart failure. The present study evaluated the effects of eprosartan, a selective angiotensin II receptor antagonist, on renal hemodynamic and excretory parameters and on the development of cardiac hypertrophy in rats with aortocaval fistula, an experimental model of congestive heart failure. Infusion of eprosartan (1.0 mg/kg) in rats with aortocaval fistula produced a significant increase (+34%) in total renal blood flow and a sustained decrease (-33%) in the calculated renal vascular resistance. These effects on renal hemodynamics were more pronounced than those observed in sham-operated control rats and occurred despite a significant fall (-12%) in mean arterial blood pressure. Moreover, eprosartan caused a preferential increase in renal cortical blood perfusion and significantly increased glomerular filtration in rats with congestive heart failure. Chronic administration of eprosartan (5.0 mg/kg per day for 7 days through osmotic minipumps inserted intraperitoneally on the day of operation) resulted in a significant enhancement of urinary sodium excretion compared with nontreated rats with heart failure. Moreover, administration of eprosartan to salt-retaining rats with congestive heart failure resulted in a progressive increase and ultimate recovery in urinary sodium excretion. Finally, early treatment with eprosartan blocked the development of cardiac hypertrophy in rats with aortocaval fistula to a larger extent than the angiotensin-converting enzyme inhibitor enalapril. These findings emphasize the importance of angiotensin II in mediating the impairment in renal function and induction of cardiac hypertrophy in heart failure and further suggest that angiotensin II receptor blockade may be a useful treatment of these consequences in severe cardiac failure.

Renal endothelin-converting enzyme in rats with congestive heart failure.

The expression and immunoreactivity of endothelin-converting enzyme (ECE) were examined in the renal tissue of rats with experimental congestive heart failure (CHF). Reverse transcriptase polymerase chain reaction (RT-PCR) revealed that ECE mRNA was more abundant (about twofold) in the renal medulla than in the cortex. Induction of heart failure caused a significant enhancement in the expression of this key enzyme in the renal cortex of rats with compensated CHF (delta + 28%) and in animals with decompensated heart failure (delta + 58%). An identical trend was also observed in the renal medulla, although these increases were moderate compared to those in the cortex. Similar findings were observed with Western blot techniques applying two monoclonal antibodies to rat ECE (AEC32-236 and AEC27-121). Taken together, these data suggest that upregulation of ECE is an important component in the activated renal ET system in CHF.