Postnatal time frame for renal vulnerability to enalapril in rats

Translational insights into mechanisms and preventive strategies after renal injury in neonates

Adverse perinatal circumstances can cause acute kidney injury (AKI) and contribute to chronic kidney disease (CKD). Accumulating evidence indicate that a wide spectrum of perinatal conditions interferes with normal kidney development and ultimately leads to aberrant kidney structure and function later in life. The present review addresses the lack of mechanistic knowledge with regard to perinatal origins of CKD and provides a comprehensive overview of pre- and peri-natal insults, including genetic predisposition, suboptimal nutritional supply, obesity and maternal metabolic disorders as well as placental insufficiency leading to intrauterine growth restriction (IUGR), prematurity, infections, inflammatory processes, and the need for life-saving treatments (e.g. oxygen supplementation, mechanical ventilation, medications) in neonates. Finally, we discuss future preventive, therapeutic, and regenerative directions. In summary, this review highlights the perinatal vulnerability of the kidney and the early origins of increased susceptibility toward AKI and CKD during postnatal life. Promotion of kidney health and prevention of disease require the understanding of perinatal injury in order to optimize perinatal micro- and macro-environments and enable normal kidney development.

Role of the renin-angiotensin system in kidney development and programming of adult blood pressure

Adverse events during fetal life such as insufficient protein intake or elevated transfer of glucocorticoid to the fetus may impact cardiovascular and metabolic health later in adult life and are associated with increased incidence of type 2 diabetes, ischemic heart disease and hypertension. Several adverse factors converge and suppress the fetal renin-angiotensin-aldosterone system (RAAS). The aim of this review is to summarize data on the significance of RAAS for kidney development and adult hypertension. Genetic inactivation of RAAS in rodents at any step from angiotensinogen to angiotensin II (ANGII) type 1 receptor (AT1) receptors or pharmacologic inhibition leads to complex developmental injury to the kidneys that has also been observed in human case reports. Deletion of the 'protective' arm of RAAS, angiotensin converting enzyme (ACE) 2 (ACE-2) and G-protein coupled receptor for Angiotensin 1-7 (Mas) receptor does not reproduce the AT1 phenotype. The changes comprise fewer glomeruli, thinner cortex, dilated tubules, thicker arterioles and arteries, lack of vascular bundles, papillary atrophy, shorter capillary length and volume in cortex and medulla. Altered activity of systemic and local regulators of fetal-perinatal RAAS such as vitamin D and cyclooxygenase (COX)/prostaglandins are associated with similar injuries. ANGII-AT1 interaction drives podocyte and epithelial cell formation of vascular growth factors, notably vascular endothelial growth factor (VEGF) and angiopoietins (Angpts), which support late stages of glomerular and cortical capillary growth and medullary vascular bundle formation and patterning. RAAS-induced injury is associated with lower glomerular filtration rate (GFR), lower renal plasma flow, kidney fibrosis, up-regulation of sodium transporters, impaired sodium excretion and salt-sensitive hypertension. The renal component and salt sensitivity of programmed hypertension may impact dietary counseling and choice of pharmacological intervention to treat hypertension.

When Less or More Isn't Enough: Renal Maldevelopment Arising From Disequilibrium in the Renin-Angiotensin System

Environmental and nutritional factors during fetal and neonatal life can have long-lasting effects on renal functions and physiology and susceptibility to kidney disease in adulthood. All components of the renin-angiotensin system (RAS) are highly expressed in the kidneys during the period of renal development. The RAS plays a central role in the regulation of various cellular growth factors and stimulates adhesion molecules and cellular migration. The use of antagonists of this system during fetal development represents a major risk factor for hypertension, renal vascular dysfunction, and kidney medulla atrophy in adulthood. The inappropriate activation of the RAS by vitamin D (VitD) deficiency has been studied in recent years. Clinical and experimental studies have demonstrated an inverse relationship between circulating VitD levels and blood pressure, plasma and renin activity, and an increase in angiotensin II and the receptor AT₁. These data raise new questions about the importance of the integrity of the RAS during development since RAS pathway inhibitors and VitD deficiency have opposing functions. This is a literature review on the possible mechanisms by which antagonists of the RAS and VitD deficiency during fetal development provoke disturbances in kidney structure and function. Potential mechanisms are presented and discussed, and the possible pathways by which an imbalanced maternal RAS may negatively impact fetal development and have consequences in adulthood are also explored.

Angiotensin II-AT1-receptor signaling is necessary for cyclooxygenase-2-dependent postnatal nephron generation

Deletion of cyclooxygenase-2 (COX-2) causes impairment of postnatal kidney development. Here we tested whether the renin angiotensin system contributes to COX-2-dependent nephrogenesis in mice after birth and whether a rescue of impaired renal development and function in COX-2^-/- mice was achievable. Plasma renin concentration in mouse pups showed a birth peak and a second peak around day P8 during the first 10 days post birth. Administration of the angiotensin II receptor AT1 antagonist telmisartan from day P1 to P3 did not result in cortical damage. However, telmisartan treatment from day P3 to P8, the critical time frame of renal COX-2 expression, led to hypoplastic glomeruli, a thinned subcapsular cortex and maturational arrest of superficial glomeruli quite similar to that observed in COX-2^-/- mice. In contrast, AT2 receptor antagonist PD123319 was without any effect on renal development. Inhibition of the renin angiotensin system by aliskiren and enalapril caused similar glomerular defects as telmisartan. Administration of the AT1 receptor agonist L162313 to COX-2^-/- pups improved kidney growth, ameliorated renal defects, but had no beneficial effect on reduced cortical mass. L162313 rescued impaired renal function by reducing serum urea and creatinine and mitigated pathologic albumin excretion. Moreover, glomerulosclerosis in the kidneys of COX-2^-/- mice was reduced. Thus, angiotensin II-AT1-receptor signaling is necessary for COX-2-dependent normal postnatal nephrogenesis and maturation.

Genetic low nephron number hypertension is associated with altered expression of key components of the renin-angiotensin system during nephrogenesis

AIM

This study investigates key components of the renin-angiotensin system (RAS) which play a central role in nephrogenesis and possibly in fetal programming of arterial hypertension in adult life.

METHODS

We compared a genetic rat model with inborn nephron deficit, the Munich Wistar Fromter rat (MWF), to normotensive Wistar rats during nephrogenesis at day 19 of fetal development (E19) and at postnatal day 7 (D7).

RESULTS

At E19 renal mRNA of angiotensin II type 1a (AT1a) (-50%, P<0.05) and type 1b (AT1b) (-55%, P<0.05) receptors were significantly decreased and renal mRNA expression of angiotensin II type 2 (AT2) receptor was fivefold increased in MWF (n=8) as compared to Wistar rats (n=8). At D7 renal mRNA expression of AT1a (-42%, P<0.05) remained lower in MWF (n=8) as compared to Wistar (n=7). Renal mRNA expression of AT2 (-30%, P>0.05) decreased in MWF (n=8) to about the level of the Wistar control (n=6).

CONCLUSIONS

Altered fetal expression of key molecules of the renin-angiotensin system in MWF indicates a possible role in genetic low nephron number hypertension.

The Role of Endothelin System in Renal Structure and Function during the Postnatal Development of the Rat Kidney

Renal development in rodents, unlike in humans, continues during early postnatal period. We aimed to evaluate whether the pharmacological inhibition of Endothelin system during this period affects renal development, both at structural and functional level in male and female rats. Newborn rats were treated orally from postnatal day 1 to 20 with vehicle or bosentan (Actelion, 20 mg/kg/day), a dual endothelin receptor antagonist (ERA). The animals were divided in 4 groups: control males, control females, ERA males and ERA females. At day 21, we evaluated renal function, determined the glomerular number by a maceration method and by morphometric analysis and evaluated possible structural renal alterations by three methods: 〈alpha〉-Smooth muscle actin (α-SMA) immunohistochemistry, Masson's trichrome and Sirius red staining. The pharmacological inhibition of Endothelin system with a dual ERA during the early postnatal period of the rat did not leads to renal damage in the kidneys of male and female rats. However, ERA administration decreased the number of glomeruli, the juxtamedullary filtration surface area and the glomerular filtration rate and increased the proteinuria. These effects could predispose to hypertension or renal diseases in the adulthood. On the other hand, these effects were more pronounced in male rats, suggesting that there are sex differences that could be greater later in life. These results provide evidence that Endothelin has an important role in rat renal postnatal development. However these results do not imply that the same could happen in humans, since human renal development is complete at birth.

The interplay between drugs and the kidney in premature neonates

The kidney plays a central role in the clearance of drugs. However, renal drug handling entails more than glomerular filtration and includes tubular excretion and reabsorption, and intracellular metabolization by cellular enzyme systems, such as the Cytochrome P450 isoenzymes. All these processes show maturation from birth onwards, which is one of the reasons why drug dosing in children is not simply similar to dosing in small adults. As kidney development normally finishes around the 36th week of gestation, being born prematurely will result in even more immature renal drug handling. Environmental effects, such as extra-uterine growth restriction, sepsis, asphyxia, or drug treatments like caffeine, aminoglycosides, or non-steroidal anti-inflammatory drugs, may further hamper drug handling in the kidney. Dosing in preterm neonates is therefore dependent on many factors that need to be taken into account. Drug treatment may significantly hamper postnatal kidney development in preterm neonates, just like renal immaturity has an impact on drug handling. The restricted kidney development results in a lower number of nephrons that may have several long-term sequelae, such as hypertension, albuminuria, and renal failure. This review focuses on the interplay between drugs and the kidney in premature neonates.

Differential modification of enalapril in the kidneys of lean and 'programmed' obese male young rats

OBJECTIVE

We investigated whether enalapril treatment could have beneficial effects on nutritionally-programmed renal changes in postnatally overfed young rats.

METHODS

Three or 10 male pups per mother were assigned to either the Obese or Lean groups during the first 21 days of life. These pups were treated with enalapril (Obese enalapril, OE; Lean enalapril, LE) or vehicle (Obese control, OC; Lean control, LC) between 15 and 28 days. All pups had their kidneys examined at 29 days.

RESULTS

OC pups weighed more than those in the LC group between 7 and 28 days of age (P<0.05). Enalapril reduced body weights in rats from both the Obese and Lean groups between 22 and 28 days (P<0.05). Renal cell proliferation and apoptosis, glomerulosclerosis, and tubulointerstitial fibrosis were all increased by enalapril (P<0.05). Among the groups, renal cell apoptosis and serum creatinine were the highest in OE pups (P<0.05). Enalapril treatment resulted in contrasting molecular expression profiles involved in renal maturation and repair in the kidneys of the rats from the Lean and Obese groups.

CONCLUSION

Enalapril can differentially modulate renal molecular alterations in lean and postnatally overfed rats and may be not beneficial in obese young male rats.

Absence of irreversible effects of aliskiren in standard juvenile rat toxicity studies

BACKGROUND

Aliskiren is the first orally bioavailable direct renin inhibitor approved for the treatment of hypertension in adults. Juvenile toxicity studies in rats were initiated to support treatment in the pediatric population.

METHODS

In Study 1, aliskiren oral administration was initiated on postpartum day (PPD) 14, after nephrogenesis was completed, and continued through PPD 70 at doses of 0, 30, 100, and 300 mg/kg/day. In-life, clinical pathology, anatomic pathology, developmental, behavioral, reproductive, and toxicokinetics evaluations were performed. In Study 2, oral administration was initiated on PPD 8, before completion of nephrogenesis, and continued through PPD 35/36. In-life, clinical pathology, anatomic pathology, developmental, and toxicokinetics evaluations were performed.

RESULTS

With dosing initiated on PPD 8, mortality at 100 and 300 mg/kg/day and slightly increased kidney weight at 100 mg/kg/day occurred. Decreased absolute lymphocyte count at 300 mg/kg/day at the end of dosing occurred with dosing initiated on PPD 14. There were clinical signs and transient effects on body weight gains in both studies. There were no changes in other parameters. Systemic exposure was much higher on PPD 8 and 14 compared with adult rats on PPD 64.

CONCLUSIONS

All effects produced by aliskiren, including kidney effects, were reversible. Increased exposure in very young animals is considered to be the result of immature drug transporter systems.

Renin-angiotensin system in ureteric bud branching morphogenesis: implications for kidney disease

Failure of normal branching morphogenesis of the ureteric bud (UB), a key ontogenic process that controls organogenesis of the metanephric kidney, leads to congenital anomalies of the kidney and urinary tract (CAKUT), the leading cause of end-stage kidney disease in children. Recent studies have revealed a central role of the renin-angiotensin system (RAS), the cardinal regulator of blood pressure and fluid/electrolyte homeostasis, in the control of normal kidney development. Mice or humans with mutations in the RAS genes exhibit a spectrum of CAKUT which includes renal medullary hypoplasia, hydronephrosis, renal hypodysplasia, duplicated renal collecting system and renal tubular dysgenesis. Emerging evidence indicates that severe hypoplasia of the inner medulla and papilla observed in angiotensinogen (Agt)- or angiotensin (Ang) II AT 1 receptor (AT 1 R)-deficient mice is due to aberrant UB branching morphogenesis resulting from disrupted RAS signaling. Lack of the prorenin receptor (PRR) in the UB in mice causes reduced UB branching, resulting in decreased nephron endowment, marked kidney hypoplasia, urinary concentrating and acidification defects. This review provides a mechanistic rational supporting the hypothesis that aberrant signaling of the intrarenal RAS during distinct stages of metanephric kidney development contributes to the pathogenesis of the broad phenotypic spectrum of CAKUT. As aberrant RAS signaling impairs normal renal development, these findings advocate caution for the use of RAS inhibitors in early infancy and further underscore a need to avoid their use during pregnancy and to identify the types of molecular processes that can be targeted for clinical intervention.

Postnatal development of the renal medulla; role of the renin-angiotensin system

Adverse events during foetal development can predispose the individual for cardiovascular disease later in life, a correlation known as foetal programming of adult hypertension. The 'programming' events have been associated with the kidneys due to the significant role in extracellular volume control and long-term blood pressure regulation. Previously, nephron endowment and functional consequences of a low nephron number have been extensively investigated without achieving a full explanation of the underlying pathophysiological mechanisms. In this review, we will focus on mechanisms of postnatal development in the renal medulla with regard to the programming effects. The renin-angiotensin system is critically involved in mammalian kidney development and impaired signalling gives rise to developmental renal lesions that have been associated with hypertension later in life. A consistent finding in both experimental animal models and in human case reports is atrophy of the renal medulla with developmental lesions to both medullary nephron segments and vascular development with concomitant functional disturbances reaching into adulthood. A review of current knowledge of the role of the renin-angiotensin system for renal medullary development will be given.

Renin-angiotensin system in ureteric bud branching morphogenesis: insights into the mechanisms

Branching morphogenesis of the ureteric bud (UB) is a key developmental process that controls organogenesis of the entire metanephros. Notably, aberrant UB branching may result in a spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). Genetic, biochemical and physiological studies have demonstrated that the renin-angiotensin system (RAS), a key regulator of the blood pressure and fluid/electrolyte homeostasis, also plays a critical role in kidney development. All the components of the RAS are expressed in the metanephros. Moreover, mutations in the genes encoding components of the RAS in mice or humans cause diverse types of CAKUT which include renal papillary hypoplasia, hydronephrosis, duplicated collecting system, renal tubular dysgenesis, renal vascular abnormalities, abnormal glomerulogenesis and urinary concentrating defect. Despite widely accepted role of the RAS in metanephric kidney and renal collecting system (ureter, pelvis, calyces and collecting ducts) development, the mechanisms by which an intact RAS exerts its morphogenetic actions are incompletely defined. Emerging evidence indicates that defects in UB branching morphogenesis may be causally linked to the pathogenesis of renal collecting system anomalies observed under conditions of aberrant RAS signaling. This review describes the role of the RAS in UB branching morphogenesis and highlights emerging insights into the cellular and molecular mechanisms whereby RAS regulates this critical morphogenetic process.

Congenital ureteropelvic junction obstruction: human disease and animal models

Ureteropelvic junction (UPJ) obstruction is the most frequently observed cause of obstructive nephropathy in children. Neonatal and foetal animal models have been developed that mimic closely what is observed in human disease. The purpose of this review is to discuss how obstructive nephropathy alters kidney histology and function and describe the molecular mechanisms involved in the progression of the lesions, including inflammation, proliferation/apoptosis, renin-angiotensin system activation and fibrosis, based on both human and animal data. Also we propose that during obstructive nephropathy, hydrodynamic modifications are early inducers of the tubular lesions, which are potentially at the origin of the pathology. Finally, an important observation in animal models is that relief of obstruction during kidney development has important effects on renal function later in adult life. A major short-coming is the absence of data on the impact of UPJ obstruction on long-term adult renal function to elucidate whether these animal data are also valid in humans.

Urotensin-II receptor antagonism does not improve renal haemodynamics or function in rats with endotoxin-induced acute kidney injury

1. Urotensin-II (U-II) is a vasoactive peptide that influences renal haemodynamics and kidney function. The aim of the present study was to examine the effects of the selective U-II receptor antagonist, urantide, on renal haemodynamics, oxygenation and function in endotoxaemic rats. 2. Endotoxaemia was induced in Sprague-Dawley rats by an intraperitoneal dose of lipopolysaccharide (LPS; Escherichia coli O127:B8, 7.5 mg/kg). At 16 h after endotoxin was given, renal clearance experiments were carried out in thiobutabarbital anaesthetized rats. Group 1, sham-saline; group 2, sham-urantide; group 3 LPS-saline; and group 4, LPS-urantide received isotonic saline or urantide (0.2 mg/kg bolus intravenously, followed by an infusion of 1.2 mg/kg/h throughout) after baseline measurements. Kidney function, renal blood flow (RBF), and cortical and outer medullary perfusion (laser-Doppler flowmetry) and oxygen tension (Clark-type microelectrodes) were analysed during 2 h of drug administration. 3. At baseline, endotoxaemic rats showed approximately 50% reductions in glomerular filtration rate (GFR) and RBF (P < 0.05), a decline in cortical and outer medullary perfusion and pO(2) (P < 0.05), and a significant increase in mean arterial pressure (MAP; P < 0.05) compared with saline-injected controls. In sham animals, urantide in a dose that did not significantly influence MAP or RBF, increased GFR (P < 0.05 time × treatment interaction) and filtration fraction (P < 0.05 treatment effect). However, urantide had no statistically significant effects on any of the investigated variables in endotoxaemic rats. 4. These findings show that U-II, through the UT receptor, does not contribute to abnormalities in renal haemodynamics and function in endotoxaemic rats.

Effect of drugs on renal development

Many nephrotoxic effects of drugs have been described, whereas the effect on renal development has received less attention. Nephrogenesis ceases at approximately 36 weeks of gestation, indicating that drugs administered to pregnant women and to preterm-born neonates may influence kidney development. Such an effect on renal development may lead to a wide spectrum of renal malformations (congenital anomalies of the kidney and urinary tract [CAKUT]), ranging from renal agenesis to a reduced nephron number. Any of these anomalies may have long-term sequelae, and CAKUT is the primary cause for renal replacement therapy in childhood. This review focuses on research into the effect of drug treatment during active nephrogenesis during pregnancy and in preterm-born infants. Because the effects of many widely used drugs have not been unraveled thus far, more research is needed to study the effect on renal development and long-term renal sequelae after drug treatment during nephrogenesis.

High sugar intake via the renin-angiotensin system blunts the baroreceptor reflex in adult rats that were perinatally depleted of taurine

Perinatal taurine depletion leads to several physiological impairments in adult life, in part, due to taurine’s effects on the renin-angiotensin system, a crucial regulator of growth and differentiation during early life. The present study tests the hypothesis that perinatal taurine depletion predisposes adult female rats to impaired baroreceptor control of arterial pressure by altering the renin-angiotensin system. Female Sprague Dawley (SD) rats were fed normal rat chow and from conception to weaning drank 3% beta-alanine in water (taurine depletion, TD) or water alone (Control, C). Female offspring ate a normal rat chow and drank water with (G) or without (W) 5% glucose throughout the experiment. To test the possible role of the renin-angiotensin system, 50% of the rats received captopril (an angiotensin converting enzyme inhibitor, 400 mg/L) from 7 days before parameter measurements until the end of experiment. At 7-8 weeks of age, arterial pressure, heart rate, baroreflex control of heart rate and renal nerve activity were studied in either conscious, freely moving or anesthetized rats. Perinatal taurine depletion did not alter resting mean arterial pressure or heart rate in the adult female offspring that received either high or normal sugar intake. Captopril treatment slightly decreased mean arterial pressure but not heart rate in all groups. Compared to controls, only the TDG rats displayed blunted baroreflex responses. Captopril treatment normalized baroreflex sensitivity in TDG. The present data indicate that in perinatal taurine depleted female rats, the renin-angiotensin system underlines the ability of high sugar intake to blunt baroreceptor responses.

Angiotensin II promotes development of the renal microcirculation through AT1 receptors

Pharmacologic or genetic deletion of components of the renin-angiotensin system leads to postnatal kidney injury, but the roles of these components in kidney development are unknown. To test the hypothesis that angiotensin II supports angiogenesis during postnatal kidney development, we quantified CD31(+) postglomerular microvessels, performed quantitative PCR analysis of vascular growth factor expression, and measured renal blood flow by magnetic resonance. Treating rats with the angiotensin II type 1 receptor antagonist candesartan for 2 weeks after birth reduced the total length, volume, and surface area of capillaries in both the cortex and the medulla and inhibited the organization of vasa recta bundles. In addition, angiotensin II type 1 antagonism inhibited the transcription of angiogenic growth factors vascular endothelial growth factor, angiopoietin-1, angiopoietin-2, and the angiopoietin receptor Tie-2 in cortex and medulla. Similarly, Agtr1a(-/-);Agtr1b(-/-) mouse kidneys had decreased angiopoietin-1, angiopoietin-2, and Tie-2 mRNAs at postnatal day 14. To test whether increased urinary flow leads to microvascular injury, we induced postnatal polyuria with either lithium or adrenalectomy, but these did not alter vascular endothelial growth factor expression or vasa recta organization. Compared with vehicle-treated rats, renal blood flow was significantly (approximately 20%) lower in candesartan-treated rats even 14 days after candesartan withdrawal. Taken together, these data demonstrate that angiotensin II promotes postnatal expansion of postglomerular capillaries and organization of vasa recta bundles, which are necessary for development of normal renal blood flow.

Low-dose candesartan improves renal blood flow and kidney oxygen tension in rats with endotoxin-induced acute kidney dysfunction

Sepsis is associated with an activation of the renin-angiotensin system and causes acute kidney injury. The aim was to examine the effects of a low, nondepressor dose of the selective angiotensin II type 1 receptor antagonist candesartan on renal hemodynamics and function in endotoxemic rats. Endotoxemia was induced in Sprague-Dawley rats by a dose of LPS (Escherichia coli O127:B8; 7.5 mg kg(-1), i.p.). At 16 h after endotoxin administration, renal clearance experiments were performed in thiobutabarbital anesthetized rats. Study groups (1) sham-saline, (2) LPS-saline, and (3) LPS-candesartan received isotonic saline or candesartan (10 microg kg(-1), i.v.) after baseline measurements. Kidney function, renal blood flow (RBF), and cortical and outer medullary perfusion (laser-Doppler flowmetry) and oxygen tension (P(O2); Clark-type microelectrodes) were analyzed during 2 h after drug administration. At baseline, endotoxemic rats showed an approximately 50% reduction in glomerular filtration rate and RBF (P < 0.05), a decline in cortical and outer medullary perfusion, and Po2 (P < 0.05), but no significant alterations in MAP compared with saline-injected controls. Candesartan treatment significantly improved RBF (+40% +/- 6% vs. baseline), cortical perfusion (+18% +/- 3% vs. baseline), and cortical (+19% +/- 7% vs. baseline) and outer medullary (+22% +/- 10% vs. baseline) P(O2) in endotoxemic rats (P < 0.05 vs. LPS-saline). Candesartan did not significantly influence MAP or glomerular filtration rate, whereas filtration fraction was reduced by 27% +/- 5% vs. baseline (P < 0.05 vs. LPS-saline). In conclusion, candesartan, in a dose that did not significantly decrease MAP, caused renal vasodilation and markedly improved RBF and intrarenal P(O2) in endotoxemic rats. These findings suggest renoprotective effects of candesartan in sepsis.

Endothelin B receptors preserve renal blood flow in a normotensive model of endotoxin-induced acute kidney dysfunction

The aim was to investigate the role of endothelin 1 receptor subtypes in the early renal response to lipopolysaccharide (LPS) during normotensive endotoxemia with acute kidney dysfunction. Endotoxemia was induced in thiobutabarbital-anesthetized rats (n = 9 per group) by infusion of LPS (dosage, 1 mg/kg per hour i.v.). The study groups (1) sham-saline, (2) LPS-saline, (3) LPS-BQ123, (4) LPS-BQ788 and (5) LPS-BQ123 + BQ788 received isotonic saline, the ETA receptor antagonist BQ-123 (dosage, 30 nmol/kg per minute i.v.), and/or the ETB receptor antagonist BQ-788 (dosage, 30 nmol/kg per minute i.v.) before and during 2 h of LPS infusion. Renal clearance measurements, renal blood flow (RBF), and cortical and outer medullary perfusion (laser-Doppler flowmetry) and oxygen tension (Clark-type microelectrodes) were analyzed throughout. Before LPS administration, there were no significant differences between groups in glomerular filtration rate (GFR), RBF, or in cortical (CLDF) and outer medullary perfusion. However, mean arterial pressure (MAP) was elevated in LPS-BQ788 group compared with LPS-BQ123 + BQ788 group (P < 0.05). In saline-treated rats, endotoxin induced an approximate 35% reduction in GFR (P < 0.05), without significant effects on MAP, RBF, or on CLDF and cortical PO2. In addition, LPS increased outer medullary perfusion and PO2 (P < 0.05). The fractional urinary excretion rates of sodium, potassium, and water were not significantly different in LPS-saline group compared with sham-saline group. Neither selective nor combined ETA and ETB receptor blockade improved GFR. In BQ-788-infused rats, endotoxin produced marked reductions in RBF (-18% +/- 4% [P < 0.05]) and CLDF (-18% +/- 2% [P < 0.05]). Similarly, endotoxin decreased RBF (-14% +/- 3% [P < 0.05]) and CLDF (-10% +/- 2% [P < 0.05]) in LPS-BQ123 + BQ788 group. Endotoxin reduced MAP (-22% +/- 4% [P < 0.05]) in BQ-123-treated rats but did not significantly influence MAP in other groups. We conclude that in early normotensive endotoxemia, ETB receptors exert a renal vasodilator influence and contribute to maintain normal RBF.

Placental insufficiency results in temporal alterations in the renin angiotensin system in male hypertensive growth restricted offspring

Reduced uterine perfusion initiated in late gestation in the rat results in intrauterine growth restriction (IUGR) and development of hypertension by 4 wk of age. We hypothesize that the renin angiotensin system (RAS), a regulatory system important in the long-term control of blood pressure, may be programmed by placental insufficiency and may contribute to the etiology of IUGR hypertension. We previously reported that RAS blockade abolished hypertension in adult IUGR offspring; however, the mechanisms responsible for the early phase of hypertension are unresolved. Therefore, the purpose of this study was to examine RAS involvement in early programmed hypertension and to determine whether temporal changes in RAS expression are observed in IUGR offspring. Renal renin and angiotensinogen mRNA expression were significantly decreased at birth (80 and 60%, respectively); plasma and renal RAS did not differ in conjunction with hypertension (mean increase of 14 mmHg) in young IUGR offspring; however, hypertension (mean increase of 22 mmHg) in adult IUGR offspring was associated with marked increases in renal angiotensin-converting enzyme (ACE) activity (122%) and renal renin and angiotensinogen mRNA (7-fold and 7.4-fold, respectively), but no change in renal ANG II or angiotensin type 1 receptor. ACE inhibition (enalapril, 10 mg x kg(-1) x day(-1), administered from 2 to 4 wk of age) abolished hypertension in IUGR at 4 wk of age (decrease of 15 mmHg, respectively) with no significant depressor effect in control offspring. Therefore, temporal alterations in renal RAS are observed in IUGR offspring and may play a key role in the etiology of IUGR hypertension.

Postnatal food restriction in the rat as a model for a low nephron endowment

A low nephron endowment may be associated with hypertension. Nephrogenesis is the process that leads to the formation of nephrons until week 36 of gestation in humans and may be inhibited by many factors like intrauterine growth restriction and premature birth. To study the consequences of a low glomerular number, animal models have been developed. We describe a model of postnatal food restriction in the rat in which litter size is increased to 20 pups, which leads to growth restriction. In the rat, active nephrogenesis continues until postnatal day 8, which coincides with the growth restriction in our model. Design-based stereological methods were used to estimate glomerular number and volume. Our results show an ∼25% lower glomerular number in rats after postnatal food restriction (30,800 glomeruli/kidney) compared with control rats (39,600 glomeruli/kidney, P < 0.001). Mean glomerular volume was increased by 35% in the growth-restricted rats ( P = 0.006). There was a significant negative correlation between glomerular volume and glomerular number ( r = −0.76, P < 0.001). We conclude that postnatal food restriction in the rat leads to a low nephron endowment with compensatory enlargement. It is therefore a suitable model to study the effect of intrauterine growth restriction or prematurity on kidney development and the consequences of a reduced glomerular number in later life.

Effects of thrombin inhibition with melagatran on renal hemodynamics and function and liver integrity during early endotoxemia

Sepsis is associated with an activation of the coagulation system and multiorgan failure. The aim of the study was to examine the effects of selective thrombin inhibition with melagatran on renal hemodynamics and function, and liver integrity, during early endotoxemia. Endotoxemia was induced in thiobutabarbital-anesthetized rats by an intravenous bolus dose of lipopolysaccharide (LPS; 6 mg/kg). Sham-Saline, LPS-Saline, and LPS-Melagatran study groups received isotonic saline or melagatran immediately before (0.75 micromol/kg iv) and continuously during (0.75 micromol.kg(-1).h(-1) iv) 4.5 h of endotoxemia. Kidney function, renal blood flow (RBF), and intrarenal cortical and outer medullary perfusion (OMLDF) measured by laser-Doppler flowmetry were analyzed throughout. Markers of liver injury and tumor necrosis factor (TNF)-alpha were measured in plasma after 4.5 h of endotoxemia. In addition, liver histology and gene expression were examined. Melagatran treatment prevented the decline in OMLDF observed in the LPS-Saline group (P < 0.05, LPS-Melagatran vs. LPS-Saline). However, melagatran did not ameliorate reductions in mean arterial pressure, RBF, renal cortical perfusion, and glomerular filtration rate or attenuate tubular dysfunctions during endotoxemia. Melagatran reduced the elevated plasma concentrations of aspartate aminotransferase (-34 +/- 11%, P < 0.05), alanine aminotransferase (-21 +/- 7%, P < 0.05), bilirubin (-44 +/- 9%, P < 0.05), and TNF-alpha (-32 +/- 14%, P < 0.05) in endotoxemia. Melagatran did not diminish histological abnormalities in the liver or the elevated hepatic gene expression of TNF-alpha, intercellular adhesion molecule-1, and inducible nitric oxide synthase in endotoxemic rats. In summary, thrombin inhibition with melagatran preserved renal OMLDF, attenuated liver dysfunction, and reduced plasma TNF-alpha levels during early endotoxemia.

Genetic low nephron number hypertension is associated with dysregulation of the hepatic and renal insulin-like growth factor system during nephrogenesis

OBJECTIVE

Low nephron number may represent a major determinant of human primary hypertension in adult life. This hypothesis is supported by a genetic rat model, namely the Munich-Wistar-Frömter (MWF) rat, which demonstrates an inherited deficit in nephron number and the development of spontaneous hypertension. Insulin-like growth factor (IGF) I and II exert endocrine and paracrine effects that are required for normal growth and nephron development. We tested the hypothesis that low nephron number is already present during fetal development, and the expression pattern of important molecules of the IGF system is altered in MWF rat during the critical period of kidney development.

METHODS

We compared MWF and normal Wistar rats during nephrogenesis at day 19 of fetal development (E19) and adult rats at postnatal day 100 (D100). Histomorphometric analysis was performed by stereological methods. Quantitative messenger RNA and protein expression was determined by real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

At E19, glomerular density (-32%) and hepatic mRNA (-48%) and protein (-18%) expression of IGF-I were decreased (P < 0.05, respectively), whereas renal mRNA expression of IGF-II receptor (+52%) and IGF binding protein 3 (+113%) were increased in MWF compared with Wistar rats (P < 0.05, respectively). Systolic blood pressure, urinary albumin excretion, and mean glomerular area were significantly elevated in MWF compared with Wistar rats at D100 (P < 0.05, respectively).

CONCLUSIONS

The fetal expression of IGF system molecules in the MWF rat model points towards a link between the decreased availability of active IGF-I and IGF-II and the fetal development of low nephron number, with manifestation of genetic hypertension in adult life.

Consequences of Intrauterine Growth Restriction for the Kidney

Low birth weight due to intrauterine growth restriction is associated with various diseases in adulthood, such as hypertension, cardiovascular disease, insulin resistance and end-stage renal disease. The purpose of this review is to describe the effects of intrauterine growth restriction on the kidney. Nephrogenesis requires a fine balance of many factors that can be disturbed by intrauterine growth restriction, leading to a low nephron endowment. The compensatory hyperfiltration in the remaining nephrons results in glomerular and systemic hypertension. Hyperfiltration is attributed to several factors, including the renin-angiotensin system (RAS), insulin-like growth factor (IGF-I) and nitric oxide. Data from human and animal studies are presented, and suggest a faltering IGF-I and an inhibited RAS in intrauterine growth restriction. Hyperfiltration makes the kidney more vulnerable during additional kidney disease, and is associated with glomerular damage and kidney failure in the long run. Animal studies have provided a possible therapy with blockage of the RAS at an early stage in order to prevent the compensatory glomerular hyperfiltration, but this is far from being applicable to humans. Research is needed to further unravel the effect of intrauterine growth restriction on the kidney.

Acute effects of the superoxide dismutase mimetic tempol on split kidney function in two-kidney one-clip hypertensive rats

OBJECTIVE

To investigate the acute effects of the superoxide dismutase mimetic 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (tempol) on split kidney function, and renal haemodynamics, in two-kidney, one-clip (2K1C) hypertensive rats.

METHODS

Three weeks after clipping, or the sham procedure, the effects of intravenous tempol (200 micromol/kg per h) were evaluated on thiobutabarbital anaesthetized Sprague-Dawley rats.

RESULTS

Mean arterial pressure (MAP; 152 +/- 3 versus 122 +/- 3 mmHg, P < 0.001), plasma renin activity (28.7 +/- 3.0 versus 9.5 +/- 0.6 ng/ml per h, P < 0.001) and urinary 8-iso-prostaglandin F2alpha excretion (124 +/- 4 versus 92 +/- 10 pmol/24 h, P = 0.003) were significantly elevated in 2K1C rats compared with sham. Tempol reduced MAP by 15 +/- 1% compared with baseline (P < 0.001) in 2K1C rats. In clipped kidneys, tempol increased the glomerular filtration rate (GFR; +50 +/- 15% from baseline) and the effective renal plasma flow (ERPF; +37 +/- 13%, from baseline), and reduced renal vascular resistance (RVR; -32 +/- 6% from baseline) compared with saline-treated controls (P < 0.05). In non-clipped kidneys, tempol reduced RVR (-24 +/- 5% from baseline) compared with saline-treated controls (P = 0.001). In sham-operated rats, tempol produced a modest reduction in MAP (-8 +/- 2% from baseline, P = 0.003), but did not significantly affect renal haemodynamics or function.

CONCLUSION

Tempol reduced MAP and RVR in both clipped and non-clipped kidneys of 2K1C hypertensive rats. In addition, tempol increased ERPF and GFR in the clipped kidney. These findings suggest important roles for superoxide in the regulation of renal haemodynamics during the early maintenance phase of renovascular hypertension.

N-acetylcysteine attenuates kidney injury in rats subjected to renal ischaemia-reperfusion

BACKGROUND

The aim of the present study is to examine the effects of N-acetylcysteine (NAC), a thiol-containing anti-oxidant, on renal function and morphology, and biomarkers of oxidative stress, in rats subjected to renal ischaemia-reperfusion (IR).

METHODS

Sprague-Dawley rats underwent unilateral nephrectomy and either contralateral renal IR (40 min of renal arterial clamping), or sham manipulation. Treatment groups were: (1) IR-Saline, (2) IR-NAC, (3) Sham-Saline and (4) Sham-NAC. The N-acetylcysteine was administered in a dose of 200 mg/kg intraperitoneally at 24, 12 and 2 h before, and 24, 48 and 72 h after, renal IR. Plasma creatinine was measured on days 1, 3 and 7 after IR, and kidney histology was assessed on day 7. In separate groups of animals we measured renal levels of the anti-oxidant glutathione, markers of systemic oxidative stress (plasma ascorbyl radical, urinary 8-iso-prostaglandin F2alpha), and glomerular filtration rate (GFR) by 51Cr-EDTA clearance, on day 1 after renal IR.

RESULTS

Treatment with NAC ameliorated the decline in GFR and reduced hyperkalaemia on day 1 (P<0.05), lowered plasma creatinine levels on days 1 and 3 (P<0.05), and decreased renal interstitial inflammation on day 7 (P<0.05), after renal IR. Kidney glutathione levels decreased significantly in group IR-Saline in response to IR (P<0.05), but were completely repleted in group IR-NAC. Groups with renal IR injury and acute renal failure showed increased plasma ascorbyl radical levels, and elevated urinary 8-iso-prostaglandin F2alpha excretion, compared with sham (P<0.05). N-acetylcysteine treatment reduced plasma ascorbyl concentrations 24 h after renal IR (P<0.05), but had no effect on the rate of urinary 8-iso-prostaglandin F2alpha excretion.

CONCLUSIONS

N-acetylcysteine improves kidney function, and reduces renal interstitial inflammation, in rats subjected to renal IR. These effects were associated with increased renal glutathione levels, and decreased plasma ascorbyl concentrations, suggesting that NAC attenuates renal and systemic oxidative stress in this model.

EFFECTS OF N-ACETYL-l-CYSTEINE ON RENAL HAEMODYNAMICS AND FUNCTION IN EARLY ISCHAEMIA-REPERFUSION INJURY IN RATS

1. Renal ischaemia-reperfusion (IR) severely compromises kidney function and has been shown to cause persistent abnormalities in intrarenal blood flow. The aim of the present study was to examine whether N-acetyl-L-cysteine (NAC), a thiol-containing anti-oxidant, improves renal haemodynamics and function during early reperfusion in rats subjected to renal IR. 2. Male Sprague-Dawley rats were divided into groups receiving either isotonic saline (IR-Saline; n = 8) or NAC (IR-NAC; n = 8) prior to (200 mg/kg, i.p., 24 and 12 h before acute experimentation) and during acute renal clearance experiments (bolus 150 mg/kg followed by a continuous infusion of 43 mg/kg per h, i.v.). During acute experimentation, thiobutabarbital-anaesthetized rats were subjected to a right-sided nephrectomy, followed by left kidney IR (40 min renal artery occlusion). Left kidney function and blood flow and intrarenal cortical and outer medullary perfusion measured by laser-Doppler flowmetry was analysed at baseline, during ischaemia and for 80 min of reperfusion. 3. Renal IR produced an approximate 85% reduction in glomerular filtration rate (GFR) and a pronounced increase in fractional urinary sodium excretion, throughout reperfusion, with no statistically significant differences between groups. 4. During reperfusion, total renal blood flow and cortical and outer medullary perfusion rapidly returned to levels not significantly different from baseline in both groups. The relative increase in renal vascular resistance in response to IR was more pronounced in NAC-treated rats compared with saline-treated animals (P < 0.05). 5. In conclusion, treatment with NAC did not improve kidney function during the first 80 min after renal IR. In addition, the marked reduction in GFR following reperfusion was not associated with any detectable abnormalities in intrarenal perfusion.

Sex-specific effects of prenatal low-protein and carbenoxolone exposure on renal angiotensin receptor expression in rats

Experimental models have shown the developing cardiovascular and renal systems to be sensitive to mild shifts in maternal nutrition, leading to altered function and risk of disease in adult life. The offspring of Wistar rats fed a low-protein diet during pregnancy exhibit a reduced nephron number and hypertension in postnatal life, providing a useful tool to examine the mechanistic basis of programming. Evidence indicates that upregulation of the renin-angiotensin system plays an important role, in particular through receptor-mediated changes in angiotensin II activity. However, although programmed hypertension has proven dependent on maternal glucocorticoids, there appear to be conflicting effects of prenatal low-protein and glucocorticoid exposure on postnatal angiotensin receptor expression. This study aimed to resolve this issue by comparing the effects of low-protein and glucocorticoid exposures on postnatal nephron number and angiotensin receptor expression. In addition, this study examined the modulation of prenatal treatment effects by postnatal inhibition of type 1 angiotensin receptor. The data demonstrates that whereas prenatal low-protein and glucocorticoid exposure have a similar effect in reducing nephron number, there are age- and gender-related differences in their effects on postnatal angiotensin receptor expression. In addition, this study provides novel evidence of a substantial upregulation of type 2 angiotensin receptor expression in low-protein- and glucocorticoid-exposed female offspring at 20 weeks of age, with implications for subsequent renal remodeling and function. Despite being targeted to the postnephrogenic period, inhibition of type 1 angiotensin receptor had an inhibitory effect on renal and somatic growth, additionally indicating its unsuitability during early life.

Renal haemodynamics and function in weanling rats treated with enalapril from birth

1. Inhibition of the renin-angiotensin system (RAS) during kidney development produces chronic alterations in renal morphology and function that have been characterized in detail in adult animals. The aim of the present study was to determine the consequences of neonatal angiotensin-converting enzyme (ACE) inhibition on renal haemodynamics and function in rats at a much earlier age, namely 3-4 weeks. 2. Male Wistar pups received daily intraperitoneal injections of enalapril (10 mg/kg) or isotonic saline from birth until 24-28 days of age, when renal haemodynamics and function were assessed using clearance techniques under pentobarbital anaesthesia. 3. Enalapril-treated rats showed significant reductions in glomerular filtration rate (GFR; -44 +/- 6%; P < 0.05), effective renal plasma flow (ERPF; -33 +/- 6%; P < 0.05) and filtration fraction (-16 +/- 3%; P < 0.05) compared with saline-treated controls. Although mean arterial pressure tended to be lower in enalapril-treated rats, this group demonstrated a significant increase in renal vascular resistance compared with control rats (RVR; 46 +/- 6 vs 32 +/- 3 mmHg/mL per.min per g.kidney weight, respectively; P < 0.05). In enalapril-treated rats, urine osmolality was reduced (-59 +/- 5%; P < 0.05) and urine flow rate and fractional urinary excretion rates of sodium and potassium were markedly elevated compared with controls (P < 0.05). Enalapril-treated rats showed severe renal histological abnormalities, including wall thickening of cortical arterioles, papillary atrophy and tubulointerstitial alterations, mimicking those described previously in similarly treated rats examined in adulthood. 4. In conclusion, neonatal ACE inhibition in rats induces pronounced alterations in renal haemodynamics and function, characterized by reductions in ERPF and GFR, increased RVR and impaired tubular sodium and water reabsorption, which are evident at weaning.

Effects of ACE inhibition during fetal development on cardiac microvasculature in adult spontaneously hypertensive rats

BACKGROUND

Early angiotensin-converting enzyme (ACE) inhibition is able to re-program spontaneously hypertensive rats (SHR) to express an attenuated form of disease in adulthood.

METHODS

Three groups of animals (n=5 each) were studied: Wistar male rats, SHR males, and SHR males obtained from dams treated with enalapril maleate (15 mg/kg/day) during gestation. Animals were sacrificed 180 days after birth, and hearts were removed for stereological quantification. Volume [Vv] (myocytes, cardiac interstitium and intramyocardial vessels), length [Lv] (intramyocardial vessels), surface [Sv] densities (myocyte and intramyocardial vessels), and the mean cross-sectional area [a] (myocyte) were estimated.

RESULTS

Blood pressure (BP) was lower in Wistar group, higher in SHR group, and intermediate in SHR-enalapril group (respectively: 122+/-8.4, 194+/-11.4, and 158+/-7.6 mm Hg, p<0.0001). Increased Vv (p=0.016), Lv (p<0.01), and Sv (p<0.01) of intramyocardial vessels were observed in SHR-enalapril group when compared to untreated SHR. A small but significant reduction was observed in a of myocytes (p=0.045).

CONCLUSION

Prenatal ACE inhibition resulted in partial hypertension attenuation as well as left ventricular hypertrophy (LVH). The positive impact on the vascular compartment came along with little or no difference in myocytes and interstitium, suggesting the involvement of a direct mechanism.

Neonatal ACE inhibition in rats interferes with lung development

The renin-angiotensin system (RAS) is developmentally up-regulated and it is essential for kidney development in several species. Given the fact that the rat lung undergoes postnatal development, the mammalian lung possesses the highest angiotensin-converting enzyme (ACE) levels and ACE activity increases during the first weeks postpartum, we tested the hypothesis that ACE inhibition influences postnatal lung development. Rats were given the ACE inhibitor enalapril (10 mg kg(-1)) from 0 to 9 days of age and their lungs were examined at day 4 and 9. Lung structure was evaluated by means of light microscopy, and surface tension of bronchoalveolar lavage fluid was measured by means of a Wilhelmy balance. Neonatal ACE inhibition lowered the surface tension of bronchoalveolar lavage fluid and caused widening of respiratory airspaces and thinning of alveolar septa. Our results suggest that early postnatal ACE inhibition in rats interferes with lung development.

Perturbed medullary tubulogenesis in neonatal rat exposed to renin-angiotensin system inhibition

BACKGROUND

Pharmacological interruption of the angiotensin II type-1 receptor (AT(1)) signalling during nephrogenesis in rats induces irreversible abnormalities in kidney morphology, comprising papillary atrophy and tubulointerstitial damage, which are characterized by tubular dilatation/atrophy and interstitial inflammation/fibrosis. This study determined the time course for development of tubular structural and inflammatory changes and possible cytokine production in the renal medulla of newborn rats exposed to angiotensin-converting enzyme (ACE) inhibition. Additionally, medullary expression of E-cadherin, a marker for tubular formation, was investigated in ACE-inhibited rats.

METHODS

Newborn rats were exposed (postnatal days 0-12) to ACE inhibitor enalapril and killed at days 1, 2, 4, 9 and 13. One kidney was used for morphological evaluation and the other for immunohistochemistry, using antibodies directed against monocytes/macrophages, T cells and E-cadherin on frozen sections. In a separate experiment, rats were treated for 9 days and had their kidneys processed for western immunoblot and immunohistochemistry, where antibodies directed against monocyte chemoattractant protein-1 (MCP-1) and tumour necrosis factor-alpha (TNF-alpha) were used on paraffin sections.

RESULTS

In renal medulla from enalapril-treated rats, volume fractions of tubular lumens and interstitium were increased from postnatal days 2 and 4, respectively, while that of tubular cells was decreased from 4 days of age. Concomitant loss and/or reduction in E-cadherin expression (from day 2) was observed in dilated medullary tubules of enalapril-treated rats. Furthermore, in the medulla of enalapril-treated rats, the increased number of ED2+ (resident macrophages) cells, followed by the increase in ED1+ (monocytes/macrophages) and CD4+ T cells, was observed at days 9 and 13, respectively. This was accompanied by increased medullary expression of TNF-alpha at day 9.

CONCLUSIONS

Neonatal ACE inhibition perturbs medullary tubulogenesis, as indicated by tubular dilatation and a lack of E-cadherin expression in these tubules. Macrophage/monocyte-mediated immune response is a secondary event, coincidentally associated with the up-regulation of TNF-alpha.

Expression and role of angiotensin II type 2 receptor in the kidney and mesangial cells of spontaneously hypertensive rats

Angiotensin II type 2 (AT2) receptor is developmentally regulated and exerts antiproliferative and proapoptotic actions. Genetic ablation of this receptor in mice affects regulation of blood pressure, but the involvement of the AT2 receptor in the pathogenesis of hypertension remains unknown. In the present study, we examined developmental changes of angiotensin receptor subtypes in the kidney of stroke-prone spontaneously hypertensive rats (SHRSP), and compared them with those in normotensive Wistar-Kyoto rats (WKY). We also investigated the regulation and functional role of the AT2 receptor in cultured mesangial cells. Receptor binding and Northern blot analyses revealed that AT2 receptor expression is significantly lower in the SHRSP kidney than in the WKY kidney during the perinatal period, while AT1 receptor expression is not different between them. In WKY mesangial cells, AT2 receptor stimulation exerted a potent antiproliferative effect; this effect was not observed in SHRSP cells lacking the AT2 receptor expression. The expression of interferon regulatory factor (IRF)-1 paralleled the growth-dependent induction of AT2 receptor in WKY mesangial cells, and transfection of IRF-1 antisense oligonucleotide significantly suppressed AT2 receptor expression, indicating IRF-1-dependent regulation of AT2 receptor expression in mesangial cells. However, this induction was inefficient in SHRSP cells. Thus, we found impaired AT2 receptor expression in the SHRSP kidney in vivo and in mesangial cells in vitro. The unbalanced expression of renal angiotensin receptor subtypes with exaggerated AT1 receptor signaling during early life in SHRSP may play a role in the programming for hypertension and related renal injury.

An intact renin-angiotensin system is a prerequisite for normal renal development

All components of the renin-angiotensin system (RAS) are highly expressed in the developing kidney in a pattern that suggests a role for angiotensin II in renal development In support of this notion, pharmacological interruption of angiotensin II type-1 (AT1) receptor-mediated effects in animals with an ongoing nephrogenesis produces specific renal abnormalities characterized by papillary atrophy, abnormal wall thickening of intrarenal arterioles, tubular atrophy associated with expansion of the interstitium, and a marked impairment in urinary concentrating ability. Similar changes in renal morphology and function also develop in mice with targeted inactivation of the genes that encode angiotensinogen, angiotensin converting enzyme, or both AT1 receptor isoforms simultaneously. Taken together, these results clearly indicate that an intact signalling through AT1 receptors is a prerequisite for normal renal development In a recent study, an increased incidence of congenital anomalies of the kidney and urinary tract was detected in mice deficient in the angiotensin II type-2 receptor, suggesting that this receptor subtype is also involved in the development of the genitourinary tract The present report mainly reviews the renal abnormalities that have been induced by blocking the RAS pharmacologically or by gene targeting in experimental animal models. In addition, pathogenetic mechanisms and clinical implications are discussed.