DNA copy number variants: A potentially useful predictor of early onset renal failure in boys with posterior urethral valves.

INTRODUCTION: Posterior urethral valves (PUV) are among the most common urological causes of chronic kidney disease (CKD) in childhood. Recently, genomic imbalances have been cited as potential risk factors for altered kidney function and have been associated with CKD. The phenotypic effects of a copy number variant (CNV) in boys with PUV are unknown. Here, it was hypothesised that the progression to early renal failure in PUV patients may be influenced by genetic aberrations. OBJECTIVE: To assess the relationship between CNVs and renal outcomes. PATIENTS AND METHODS: Between September 2012 and July 2015, 45 children with PUV were recruited to evaluate the presence of CNVs in their DNA. The patients' medical records were retrospectively reviewed. The criteria for outcomes of renal function included: assessments of the nadir serum creatinine in the first year of life, the estimated glomerular filtration rate at 1 and 5 years, and the requirement for renal replacement. RESULTS: Thirteen CNVs were identified in 12 boys (29% of the cohort). Microarray analysis revealed two pathogenic CNVs (well-established CNVs known to be associated with genetic disease) and 11 of unknown significance (CNVs with insufficient current available evidence for unequivocal determination of clinical significance), including genes that have been previously implicated in kidney diseases and urogenital disorders. The median follow-up was 10.2 years (range 3-17.5) in the group of patients with CNV compared with 5.8 years (range 1-16.6) in those CNV-. The nadir creatinine values were significantly higher in boys with CNVs than in those without CNVs (57.5 µmol/L (range 23-215) and 28 µmol/L (range 18-155), respectively (P = 0.05) (Figure). Boys CNV+ had a worse prognosis, with a higher incidence of Stage-V CKD compared with the control group (33% with CNVs vs. 9% in CNV-, P = 0.06) at a median age of 22 months (range 8 months-16 years). Four (33%) patients CNV+ underwent renal transplantation. DISCUSSION: The role of CNVs in the deterioration of renal function remains unknown. It can be hypothesised that CNVs could be a contributing factor or may serve as an accelerant for the progression to renal failure. CONCLUSION: The CNVs >100 Kb were significantly associated with early onset renal failure in children with PUV. Prenatal detection of CNV could help to identify foetuses at high risk of severe renal impairment in cases of suspected PUV, especially in cases without oligohydramnios or severe pulmonary hypoplasia. These preliminary results should be confirmed in a larger cohort of patients.

Indomethacin administered early in the postnatal period results in reduced glomerular number in the adult rat.

Indomethacin and ibuprofen are administered to close a patent ductus arteriosus (PDA) during active glomerulogenesis. Light and electron microscopic glomerular changes with no change in glomerular number were seen following indomethacin and ibuprofen treatment during glomerulogenesis at 14 days after birth in a neonatal rat model. This present study aimed to determine whether longstanding renal structural changes are present at 30 days and 6 mo (equivalent to human adulthood). Rat pups were administered indomethacin or ibuprofen antenatally on days 18-20 (0.5 mg·kg(-1)·dose(-1) indomethacin; 10 mg·kg(-1)·dose(-1) ibuprofen) or postnatally intraperitoneally from day 1 to 3 or day 1 to 5 (0.2 mg·kg(-1)·dose(-1) indomethacin; 10 mg·kg(-1)·dose(-1) ibuprofen). Control groups received no treatment or normal saline intraperitoneally. Pups were killed at 30 days of age and 6 mo of age. Tissue blocks from right kidneys were prepared for light and electron microscopic examination, while total glomerular number was determined in left kidneys using unbiased stereology. Eight pups were included in each group from 14 maternal rats. At 30 days and 6 mo, there were persistent electron microscopy abnormalities of the glomerular basement membrane in those receiving postnatal indomethacin and ibuprofen. There were no significant light microscopy findings at 30 days or 6 mo. At 6 mo, there were significantly fewer glomeruli in those receiving postnatal indomethacin but not ibuprofen (P = 0.003). In conclusion, indomethacin administered during glomerulogenesis appears to reduce the number of glomeruli in adulthood. Alternative options for closing a PDA should be considered including ibuprofen as well as emerging therapies such as paracetamol.

Alcohol exposure during late gestation: multiple developmental outcomes in sheep.

Alcohol consumption during pregnancy remains common in many countries. Exposure to even low amounts of alcohol (i.e. ethanol) in pregnancy can lead to the heterogeneous fetal alcohol spectrum disorders (FASD), while heavy alcohol consumption can result in the fetal alcohol syndrome (FAS). FAS is characterized by cerebral dysfunction, growth restriction and craniofacial malformations. However, the effects of lower doses of alcohol during pregnancy, such as those that lead to FASD, are less well understood. In this article, we discuss the findings of recent studies performed in our laboratories on the effects of fetal alcohol exposure using sheep, in which we investigated the effects of late gestational alcohol exposure on the developing brain, arteries, kidneys, heart and lungs. Our studies indicate that alcohol exposure in late gestation can (1) affect cerebral white matter development and increase the risk of hemorrhage in the fetal brain, (2) cause left ventricular hypertrophy with evidence of altered cardiomyocyte maturation, (3) lead to a decrease in nephron number in the kidney, (4) cause altered arterial wall stiffness and endothelial and smooth muscle function and (5) result in altered surfactant protein mRNA expression, surfactant phospholipid composition and pro-inflammatory cytokine mRNA expression in the lung. These findings suggest that fetal alcohol exposure in late gestation can affect multiple organs, potentially increasing the risk of disease and organ dysfunction in later life.

Distribution of volumes of individual glomeruli in kidneys at autopsy: association with age, nephron number, birth weight and body mass index.

BACKGROUND: Glomerular hypertrophy occurs in a number of normal and pathological states. Glomerular volume in kidneys at autopsy is usually indirectly derived from estimates of total glomerular mass and nephron number, and provides only a single value per kidney, with no indication of the range of volumes of glomeruli within the kidney of any given subject. We review findings of the distribution of volumes of different glomeruli within subjects without kidney disease, and their correlations with age, nephron number, birth weight and body mass index (BMI). METHODS: The study describes findings from autopsy kidneys of selected adult white males from the Southeast USA who had unexpected deaths, and who did not have renal scarring or renal disease. Total glomerular (nephron) number and total glomerular volume were estimated using the disector/fractionator combination, and mean glomerular volume (Vglom) was derived. The volumes of 30 individual glomeruli (IGV) in each subject were determined using the disector/Cavalieri method. IGV values were compared by categories of age, nephron number, birth weight and BMI. RESULTS: There was substantial variation in IGV within subjects. Older age, lower nephron number, lower birth weight and gross obesity were associated with higher mean IGV and with greater IGV heterogeneity. High Vglom and high IGVs were associated with more glomerulosclerosis. However, amongst the generally modest numbers of sclerosed glomeruli, the pattern was uniformly of ischemic collapse of the glomerular tuft. There was no detectable focal segmental glomerular tuft injury. DISCUSSION: In this series of people without overt renal disease, greater age, nephron deficit, lower birth weight and obesity were marked by glomerular enlargement and greater glomerular volume heterogeneity within individuals.

Transient hypertension and sustained tachycardia in mice housed individually in metabolism cages.

The novel environment of a metabolic cage can be stressful for rodents, but few studies have attempted to quantify this stress-response. Therefore, we determined the effects on mean arterial pressure (MAP) and heart rate (HR), of placing mice of both sexes in metabolism cages for 2 days. After surgical implantation of a carotid artery catheter mice recovered individually in standard cages for 5 days. Mice then spent 2 days in metabolism cages. MAP and HR were monitored in the standard cage on Day 5 and in metabolism cages on Days 6-7. MAP increased by 18+/-3 and 22+/-4 %, while HR increased by 27+/-4 and 27+/-6 %, in males and females, respectively, during the first hours after cage switch. MAP decreased to baseline in the fourth and eighth h following metabolism cage switch in males and females, respectively. However, HR remained significantly elevated in both sexes during the entire two-day period in metabolism cages. Females had lower MAP than males both pre- and post-metabolism cage switch, but there were no sex differences in HR. These results demonstrate sustained changes in cardiovascular function when mice are housed in metabolism cages, which could potentially affect renal function.

Factors influencing mammalian kidney development: implications for health in adult life.

There are many reasons why it is timely to review the development of the mammalian kidney. Perhaps the most important of these is the increasing amount of evidence to demonstrate that factors which impinge on/alter the normal developmental processes of this organ can have lifelong consequences for the health of the adult. The'Developmental Origins of Health and Adult Disease' (DOHaD) hypothesis, proposes that changes in the environment during the development of an organ or system, can have permanent deleterious effects leading to increased risk of cardiovascular and/or metabolic disease. The permanent metanephric kidney has been shown to be very vulnerable to such influences with many factors shown to alter both the permanent structure and the level of expression of important functional genes. Thus it is important to understand the precise timing of kidney development in terms of both structure and the genes involved at each stage. Such knowledge has been gained by significant advances in technology, which allow quantification of the number of nephrons by unbiased stereology, detections of both levels and site of gene expression,'knock-out' and knock-in' of genes in animal (mainly mouse) models and by the ability to examine nephron development, in real time, in culture systems.

Sex differences in postnatal growth and renal development in offspring of rabbit mothers with chronic secondary hypertension.

Previously, we demonstrated that adult blood pressure was increased in offspring of rabbit mothers with chronic secondary renal hypertension. Our study identified sex-specific differences in the programming of hypertension, with female, not male, offspring, having increased blood pressure at 30 wk of age. The aim of this study was to characterize the maternal hypertension during pregnancy to determine potential programming stimuli. Further, we examined the impact of chronic maternal hypertension on offspring birth weight, nephron number, and renal noradrenaline content (as an index of renal innervation density). Three groups of mothers and their offspring were studied: two-kidney, one-wrap (2K-1W, n = 9 mothers) hypertensive, two-kidney, two-wrap (2K-2W, n = 8) hypertensive, and a sham-operated group (n = 9). Mean arterial blood pressure was increased by approximately 20 mmHg throughout pregnancy in both hypertensive groups compared with sham mothers (P(G) < 0.001). Plasma renin activity (PRA; P(G) < 0.05) and aldosterone (P(G) < 0.05) levels were increased during gestation in the 2K-1W, but not the 2K-2W mothers. Birth weight was increased by approximately 20% in offspring of both groups of hypertensive mothers (P(T) < 0.001), though this was associated with a reduction in litter size. Renal noradrenaline content was increased ( approximately 40%, P < 0.05) at 5 wk of age in female 2K-1W offspring compared with sham offspring. Glomerular number was not reduced in female offspring of either group of hypertensive mothers; however, glomerular tuft volume was reduced in female 2K-2W offspring (P < 0.05), indicative of a reduction in glomerular filtration surface area. In conclusion, the two models of renal hypertension produced differential effects on the offspring. The impact of a stimulated maternal renin-angiotensin system in the 2K-1W model of hypertension may influence development of the renal sympathetic nerves and contribute to programming of adult hypertension.

Reduced nephron number and glomerulomegaly in Australian Aborigines: a group at high risk for renal disease and hypertension.

Aborigines in remote areas of Australia have much higher rates of renal disease, as well as hypertension and cardiovascular disease, than non-Aboriginal Australians. We compared kidney findings in Aboriginal and non-Aboriginal people in one remote region. Glomerular number and mean glomerular volume were estimated with the disector/fractionator combination in the right kidney of 19 Aborigines and 24 non-Aboriginal people undergoing forensic autopsy for sudden or unexpected death in the Top End of the Northern Territory. Aborigines had 30% fewer glomeruli than non-Aborigines--202,000 fewer glomeruli per kidney, or an estimated 404,000 fewer per person (P=0.036). Their mean glomerular volume was 27% larger (P=0.016). Glomerular number was significantly correlated with adult height, inferring a relationship with birthweight, which, on average, is much lower in Aboriginal than non-Aboriginal people. Aboriginal people with a history of hypertension had 30% fewer glomeruli than those without--250,000 fewer per kidney (P=0.03), or 500,000 fewer per person, and their mean glomerular volume was about 25% larger. The lower nephron number in Aboriginal people is compatible with their susceptibility to renal failure. The additional nephron deficit associated with hypertension is compatible with other reports. Lower nephron numbers are probably due in part to reduced nephron endowment, which is related to a suboptimal intrauterine environment. Compensatory glomerular hypertrophy in people with fewer nephrons, while minimizing loss of total filtering surface area, might be exacerbating nephron loss. Optimization of fetal growth should ultimately reduce the florid epidemic of renal disease, hypertension, and cardiovascular disease.

Hypertension, glomerular number, and birth weight in African Americans and white subjects in the southeastern United States.

Low nephron number has been related to low birth weight and hypertension. In the southeastern United States, the estimated prevalence of chronic kidney disease due to hypertension is five times greater for African Americans than white subjects. This study investigates the relationships between total glomerular number (Nglom), blood pressure, and birth weight in southeastern African Americans and white subjects. Stereological estimates of Nglom were obtained using the physical disector/fractionator technique on autopsy kidneys from 62 African American and 60 white subjects 30-65 years of age. By medical history and recorded blood pressures, 41 African Americans, and 24 white subjects were identified as hypertensive and 21 African Americans and 36 white subjects as normotensive. Mean arterial blood pressure (MAP) was obtained on 81 and birth weights on 63 subjects. For African Americans, relationships between MAP, Nglom, and birth weight were not significant. For white subjects, they were as follows: MAP and Nglom (r=-0.4551, P=0.0047); Nglom and birth weight (r=0.5730, P=0.0022); MAP and birth weight (r=-0.4228, P=0.0377). For African Americans, average Nglom of 961 840+/-292 750 for normotensive and 867 358+/-341 958 for hypertensive patients were not significantly different (P=0.285). For white subjects, average Nglom of 923 377+/-256 391 for normotensive and 754 319+/-329 506 for hypertensive patients were significantly different (P=0.03). The data indicate that low nephron number and possibly low birth weight may play a role in the development of hypertension in white subjects but not African Americans.

Quartz crystal microbalance-based measurements of shear-induced senescence in human embryonic kidney cells.

Fluid shear and other mechanical forces play an important role in the normal biophysical, biochemical, and gene regulatory responses of vertebrate tissue that are reflected in the expression of normal cell differentiation, growth, and function. Despite some promising work reported on the application of the quartz crystal microbalance (QCM) to both prokaryote and eukaryote cells over the last decade, QCM has yet to be successfully applied to cells in culture under conditions of flow-induced shear. In this study, high sensitivity QCM in conjunction with fluid modelling was used to monitor the onset of senescence in immortalised human embryonic kidney cells under laminar shear stresses of between 0.04 and 335 dyne/cm(2). The feasibility of this approach as a means of quantification and characterisation of cell physiological response and adhesion are explored and discussed.

Chemotherapy delays progression of motor neuron disease in the SOD1 G93A transgenic mouse.

BACKGROUND: A significant proliferation of glial cells occurs in the spinal cord and brainstem of SOD1 G93A transgenic mice with familial amyotrophic lateral sclerosis (ALS). Since activated glia may contribute to motor neuron degeneration, we tested whether inhibition of gliosis using low-dose chemotherapy is beneficial in this mouse model. METHODS: Mice were administered fortnightly intraperitoneal injections of 0.1 mg/kg vincristine (VIN) or saline commencing at postnatal day 68 before disease onset. Mice were sacrificed at end-stage disease, and spinal cords were examined for histology. RESULTS: Survival of VIN-treated mice was significantly increased at 132.0 +/- 4.1 days compared to control animals at 117.8 +/- 2.1 days (p < 0.05). Furthermore, analysis of microglia and astrocyte populations suggests a reduction in the former following VIN therapy. CONCLUSION: This study suggests that chemotherapy may offer an alternative therapy or co-therapy for ALS.

Angiotensin-converting enzyme inhibition in adult hypertensive rats: a stereological study of renal filtration surface area.

1. Angiotensin-converting enzyme (ACE) inhibitor treatment leads to beneficial effects on kidney function. The aim of the present study was to determine whether ACE inhibition at high or low doses affects glomerular capillary surface area and length, glomerular number or total renal filtration surface area in rats with established hypertension and, if so, to determine whether these effects are mediated through bradykinin potentiation. 2. Spontaneously hypertensive rats (SHR) were treated with the ACE inhibitor perindopril at either 3 or 0.1 mg/kg per day (high and low doses, respectively) from 16 to 24 weeks of age. Some rats were concomitantly treated with the bradykinin B2 receptor antagonist S16118 (10 nmol/kg per day). Blood pressure was measured twice weekly during the treatment period. At 24 weeks of age, rats were perfusion fixed at 140 mmHg, the kidneys removed, embedded in resin and examined stereologically to estimate glomerular number and volume, length and surface area of glomerular capillaries and total renal filtration surface area. 3. High- and low-perindopril treatment significantly reduced systolic blood pressure compared with control SHR. However, the rats treated with low-dose perindopril were still considered hypertensive. Neither low-dose nor high-dose perindopril treatment had any observable effect on glomerular number (23 876 +/- 1201 vs 26 240 +/- 1465 glomeruli/kidney, respectively) or volume (2.25 +/- 0.21 and 1.96 +/- 0.06 x 10-3 mm3, respectively) compared with controls (glomerular number 25866 +/- 1210 glomeruli/kidney; glomerular volume 2.24 +/- 0.21 x 10-3 mm3). As a result, there was no significant difference in total renal filtration surface area between any of the experimental groups (8161.6 +/- 550.9, 8699.7 +/- 427.6, 9081.9 +/- 453.6, 8830.2 +/- 521.2 and 8559.4 +/- 341.4 mm2 for SHR, SHR low-dose perindopril, SHR low-dose perindopril + B2 antagonist, SHR high-dose perindopril and SHR high-dose perindopril + B2 antagonist, respectively). Coadministration of the bradykinin antagonist had no observable effect on any of the parameters studied. 4. In conclusion, because neither high-dose nor low-dose perindopril had any effect on total renal filtration surface area, the observed beneficial effects of ACE inhibition on kidney function are not the result of enhancement in glomerular capillary surface area.

Antigen-induced airway inflammation in the Brown Norway rat results in airway smooth muscle hyperplasia.

Asthma is characterized by chronic airways inflammation, airway wall remodeling, and airway hyperresponsiveness (AHR). An increase in airway smooth muscle has been proposed to explain a major part of AHR in asthma. We have used unbiased stereological methods to determine whether airway smooth muscle hyperplasia and AHR occurred in sensitized, antigen-challenged Brown Norway (BN) rats. Ovalbumin (OA)-sensitized BN rats chronically exposed to OA aerosol displayed airway inflammation and a modest level of AHR to intravenously administered ACh 24 h after the last antigen challenge. However, these animals did not show an increase in smooth muscle cell (SMC) number in the left main bronchus, suggesting that short-lived inflammatory mechanisms caused the acute AHR. In contrast, 7 days after the last aerosol challenge, there was a modest increase in SMC number, but no AHR to ACh. Addition of FCS to the chronic OA challenge protocol had no effect on the degree of inflammation but resulted in a marked increase in both SMC number and a persistent (7-day) AHR. These results raise the possibility that increases in airway SMC number rather than, or in addition to, chronic inflammation contribute to the persistent AHR detected in this model.

Expression of bone morphogenetic protein receptors in the developing mouse metanephros.

While bone morphogenetic proteins (BMPs) 2, 4 and 7 have recently been implicated in aspects of metanephric development, and expression patterns of these ligands have been described in the developing metanephros, the distribution of BMP receptors in developing metanephroi remains unknown. In the present study, in situ hybridisation histochemistry was used to localise mRNAs for BMP type-I receptors (BMPR-IA and BMPR-IB) and the BMP type-II receptor (BMPR-II) in developing mouse metanephroi. At embryonic day 12.5 (E12.5) and E14.5 transcripts for BMP type-I receptors were localised to the tips and body of the branching ureter as well as mesenchymal condensates, developing vesicles and comma-shaped bodies. Localisation of BMPR-II transcripts was similar although expression was not observed in the body of the ureter. At E17.5, transcripts for all three receptors were localised in the nephrogenic zone including ureteric tips, vesicles, comma- and S-shaped bodies as well the body of the ureter and in tubules. BMP type-I and type-II receptor transcripts co-localised with each other, in agreement with the well-documented evidence that BMPs signal via heterotetrameric complexes of type-I and type-II receptors and with the previously reported metanephric expression pattern of BMPs. These patterns of receptor expression suggest that these molecules are important regulators of epithelial-mesenchymal interactions, nephron development and ureteric branching morphogenesis.

Effect of angiotensin-converting enzyme inhibition on renal filtration surface area in hypertensive rats.

BACKGROUND: Angiotensin-converting enzyme (ACE) inhibitor treatment leads to protective effects on the cellular structure of the glomerulus and the kidney. The aim of this study was to determine whether ACE inhibition increases renal filtration surface area in the spontaneously hypertensive rat (SHR). METHODS: SHR were treated with the ACE inhibitor perindopril at a high dose (3 mg/kg/day) or a low dose (0.1 mg/kg/day) during the period of hypertension development, from 7 to 14 weeks of age. Some animals were treated concomitantly with the bradykinin B2 receptor antagonist, S16118. Tail-cuff systolic blood pressure and body weights were measured twice weekly. At termination of treatment, glomerular number and volume, length, and surface area of glomerular capillaries and renal filtration surface area were estimated using unbiased stereological techniques. RESULTS: There were significant dose-related reductions in blood pressure with high- and low-dose perindopril treatment. Neither low- nor high-dose perindopril treatment had any effect on glomerular number or size or glomerular capillary length and surface area. Hence, there was no significant difference in total renal filtration surface area between any of the experimental groups (8721 +/- 610 mm2 in untreated SHR and 7879 +/- 338 mm2 and 8767 +/- 437 mm2 in the low and high dose perindopril-treated groups, respectively). Coadministration of the bradykinin antagonist did not affect any of the glomerular parameters. CONCLUSIONS: ACE inhibition during the period of hypertension development does not lead to an enhanced glomerular capillary growth or increases in total renal filtration surface area in this model.

Podocyte foot process broadening in experimental diabetic nephropathy: amelioration with renin-angiotensin blockade.

AIMS/HYPOTHESIS: Changes in podocyte number and morphology have been implicated in the pathogenesis of proteinuria and the progression of human and experimental kidney disease. This study sought to examine podocyte foot process and slit pore architecture in experimental diabetic nephropathy and to determine whether such changes were modified with renoprotective intervention by blockade of the renin-angiotensin system. METHODS: The number of filtration slits per 100 microm of glomerular basement membrane was assessed by transmission electron microscopy and quantitated histomorphometrically in control animals and in rats with 24 weeks of streptozotocin-induced diabetes. Diabetic rats were either untreated or received the angiotensin converting enzyme inhibitor ramipril, or the angiotensin II type 1 receptor antagonist, valsartan. RESULTS: When compared with control animals, diabetes was associated with a decrease in the number of slit pores per unit length of glomerular basement membrane, indicative of podocyte foot process broadening. Both ramipril and valsartan attenuated these ultrastructural changes to a similar degree. These differences remained after correcting for glomerular volume as a possible confounding variable. CONCLUSION/INTERPRETATION: Preservation of podocyte architecture could contribute to the renoprotective effects of renin-angiotensin system blockade in diabetic nephropathy.

Renal vascular resistance properties and glomerular protection in early established SHR hypertension.

OBJECTIVE: To characterize the in vivo vascular properties of the spontaneously hypertensive rat (SHR) renal vascular bed by examining vascular conductance/resistance responsiveness to vasoactive agents in vivo and determining whether the filtration surface area of glomerular capillaries is reduced. DESIGN AND METHODS: in vivo renal blood flow responses to intrarenally administered angiotensin II, phenylephrine and acetylcholine were compared in 10-week-old SHR and Wistar-Kyoto (WKY) rats using a wide range of doses from near threshold to near maximal effect. Unbiased stereological techniques and high-resolution light microscopy were used to estimate the surface area and length of glomerular capillaries, and evidence of capillary damage. RESULTS: The SHR renal bed demonstrated significantly enhanced dose-vascular resistance responses to vasoconstrictors. For vascular conductance and calculated radius of resistance vessels, the SHR curves were significantly lower across the full dilator-constrictor range examined, but the dose-related changes were similar to those of WKY rats. There were only modest enhancements of the renal blood flow responses in the SHR, evident only when renal blood flow was reduced by more than 50% SHR and WKY rats did not differ in mean glomerular capillary surface area (0.13+/-0.02 mm2 and 0.14+/-0.02 mm2, respectively) or length (5.76+/-0.85 mm and 5.48+/-0.90 mm, respectively) nor was there evidence of glomerular capillary damage in either strain. CONCLUSIONS: The renal vascular bed of the SHR in vivo exhibits reduced vascular conductance across a wide vasomotor range, compatible with findings in other vascular beds. We have further shown no evidence of reduced glomerular capillary surface area or damage. These findings are compatible with the hypothesis that the reduced conductance of the SHR pre-glomerular vasculature increases the aorta-capillary pressure gradient thus protecting the glomerular capillaries from systemic hypertension at this age.

Renomedullary interstitial cell lipid droplet content is increased in spontaneously hypertensive rats and by low salt diet.

OBJECTIVE: To compare the volumes of renomedullary interstitial cell (RMIC) lipid droplets (putative source of vasodepressor substance) in spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats on high and low salt diets as an indication of whether the renomedullary vasodepressor system of the SHR is defective. METHODS: Ten-week-old male SHR and WKY rats received a low (0.05% w/w) or high salt (5.0%) diet for 21 days. Conscious mean arterial pressure (MAP) was measured and the renal papilla perfusion fixed with a high osmolarity fixative. Using electron microscopic stereological techniques, the volume density of lipid in RMIC (VVLipid,RMIC) and the total volumes of lipid (VLipid) and RMIC (VRMIC) in papilla were measured. RESULTS: MAP of SHR (high 155 +/- 3 mmHg; low 151 +/- 3 mmHg) was significantly greater than WKY rats (high 126 +/- 2 mmHg; low 129 +/- 2 mmHg; P< 0.001), however salt diet had no significant effect on MAP. The VLipid of rats on the low salt diet was approximately 2.5 times greater than in rats on the high salt diet (P < 0.01). SHR had significantly greater VLipid than WKY rats irrespective of salt diet (P< 0.05; SHR-low 0.245 +/- 0.031 mm3, SHR-high 0.093 +/- 0.007 mm3; WKY-low 0.126 +/- 0.032 mm3, WKY-high 0.051 +/- 0.020 mm3). Similar differences were seen for VVLipid,RMIC, however VRMIC was not different between rat strains or salt diet groups. CONCLUSIONS: SHR and WKY rats responded similarly to the altered salt diets, and SHR demonstrated greater volumes of stored RMIC lipid droplets irrespective of the level of salt intake. These results indicate that SHR hypertension is not due to a deficiency in the amount of lipid droplets, the putative source of the renomedullary vasodepressor substance and that the renomedullary vasodepressor system of the SHR is capable of responding normally to the physiological stimulus of altered salt intake.

Nephron endowment in glial cell line-derived neurotrophic factor (GDNF) heterozygous mice.

BACKGROUND: The exact molecular mechanisms that regulate ureteric branching morphogenesis in the developing metanephros have not been fully elucidated. However, in vivo and in vitro evidence indicates that glial cell line-derived neurotrophic factor (GDNF) is a key regulator of the initiation of ureteric branching. GDNF knockout mice show renal agenesis or severe dysgenesis and die 24 hours after birth from renal failure. Inhibition of GDNF activity in metanephric organ culture inhibits ureteric branching. Since nephron initiation only occurs at the tips of ureteric branches, the aim of the present study was to determine whether nephron number in GDNF heterozygous mice is reduced. METHODS: Male GDNF heterozygous mice of hybrid 129/Sv and C57/BL genetic background were mated with C57BL/6 females. Offspring were genotyped at postnatal day 30 (PN30) by polymerase chain reaction. Left kidneys were used for estimating kidney volume and total nephron number. We also estimated absolute and relative volumes of ureteric duct epithelium. Unbiased stereological methods were used throughout (Cavalieri method, physical disector/fractionator combination). RESULTS: GDNF wild-type and heterozygous mice had similar body weights at PN30. However, heterozygous kidneys were 25% smaller than wild-type kidneys (wild-type, 114.75 +/- 16.46 mm3; heterozygous, 87.11 +/- 21.84 mm3, P < 0.001) and contained approximately 30% fewer nephrons (wild-type, 11886 +/- 1277; heterozygous, 8573 +/- 2240, P < 0.01). In addition, the absolute ureteric duct volume was significantly reduced in heterozygous mice (P < 0.001). CONCLUSIONS: : These results indicate that the loss of one GDNF allele results in reduced nephron endowment in the adult kidney, presumably as the result of reduced branching morphogenesis of the ureteric bud.