Changes within vascular bundles of rodent kidneys caused by different diets

Morphological effects caused by two different diets (low protein-high water intake, and high protein-restricted water) on the vascular bundles in the outer medullary zone of the kidney were studied in the laboratory white mouse and in the golden spiny mouse (Acomys russatus, Muridae). In both rodents, when on a low protein-high water intake diet, considerable interstitial substance was found between the vasa recta of the bundles. No interstitial substance was found in animals on high protein-low water intake diet; as a result the vasa recta of the vascular bundle adhered closely. The low protein-high water intake diet caused a marked diuresis, low urine osmolality and low urinary urea concentration. It is assumed that the increase in interstitial substance between the vasa recta of the vascular bundle lowers the efficiency of the counter current barrier system for urea in the kidney and, as a consequence, the medullary urea gradient and urine concentrating capacity decreases. In animals on a high protein diet, the closely juxtaposed vasa recta assure an efficient countercurrent exchange, leading to accumulation and maintenance of a large urea gradient in the medulla and maximal urine concentration. It is suggested that the amount of interstitial material between the vasa recta of the vascular bundle might serve as a modulating factor for the urea concentration in the kidney.     

Nephron target sites in chronic exposure to lead

With established urinary markers of kidney integrity the early renal effects of lead have previously been considered to be mainly tubular or tubulointerstitial. In a cross-sectional study on 81 male lead-exposed workers and 45 age-matched controls (median blood lead concentrations 2.03 and 0.34 mumol/l respectively) not only well-established but also new urinary markers of renal integrity preferentially or exclusively located along the different nephron segments were analysed. Markers related to the glomerulus were 6-keto-prostaglandin 1 alpha, thromboxane B2, mainly produced in the glomerulus, and the extracellular matrix protein fibronectin. Markers of the proximal tubule were the brush-border antigens BBA, BB50, and HF5 and the intestinal alkaline phosphatase. Prostaglandin E2 and F2 alpha, preferentially synthesized in the collecting duct and medullary interstitial cells, served as markers of these more distal nephron segments. In contrast to previous studies on the early phase of lead nephrotoxicity, not only tubular but also glomerular involvement could be shown in the study presented here by increases in the median values of 6-keto-prostaglandin 1 alpha and decreases in fibronectin. The proximal tubular markers intestinal alkaline phosphatase and BBA confirmed that this particular segment of the nephron is affected by lead. Effects on the collecting tubule or medullary interstitial cells could also be observed. It is concluded that lead affects both the glomerulus and the tubular apparatus and that combinations of new and established markers could be valuable for a better definition and early detection of lead nephropathy.     

Localization of ROMK channels in the rat kidney

Renal potassium secretion occurs in the distal segments of the nephron through apically located secretory potassium (SK) channels. SK may correspond to the ROMK channels cloned from rat kidney. In this study, the localization of ROMK at the cellular level in the rat kidney was examined using an affinity-purified polyclonal antibody raised against a C-terminal peptide of ROMK. The specificity of the antibody was demonstrated by immunoblots of membranes of Xenopus oocytes expressing ROMK2. Immunoblots of homogenates from rat renal outer medulla and cortex revealed predominant bands of 70 to 75 kD, which were ablated by preadsorption with an excess of peptide. These bands were specific for the rat kidney. Immunolocalization studies revealed that ROMK is expressed in specific nephron segments in both the cortex and medulla. In the cortex, ROMK was found in the apical domain of the thick ascending limb of Henle's loop, the connecting tubule, and in some, but not all, cells of cortical collecting tubules. In the medulla, expression in the apical membrane of the thick ascending limbs of Henle's loop was strong, whereas outer medullary collecting ducts were weakly stained. Expression in the thick ascending limb was also heterogeneous; some cells that expressed the Na-K-Cl cotransporter were weakly stained with the anti-ROMK antibody. No staining of glomeruli, proximal tubules, or inner medullary collecting ducts was found. The localization of ROMK agrees well with the findings of SK in patch-clamp studies and supports the view that ROMK is the SK channel of the distal segments of the nephron.     

Acid and alkaline phosphatases in the kidney of a few fishes

The localization of acid and alkaline phosphatases in the kidney of Cirrhinus reba, Ompak bimaculatus and Labeo gonius has been studied. In all these fishes, the enzymes are found in the proximal tubule. The activity of alkaline phosphatase is more stronger than acid phosphatase. The renal capsule, distal tubule, collecting tubule and interstitial hematopoietec tissue are all phosphatase negative. The activity is more stronger in the first proximal tubule than in the second tubule. It is probable that acid phosphatase is associated with the intracellular digestion of the macromolecules absorbed and alkaline phosphatase with the absorption of glucose from the tubular lumen.     

Evidence for distal tubular inhibition of calcium efflux by nisoldipine in the SHR rat

Nisoldipine, a calcium channel blocking agent, is known to have antihypertensive, renal tubular and hemodynamic effects. The present studies were designed to examine the effects of this drug on the renal tubular transport of calcium in 12 saline-loaded SHR rats. Calcium-45 was infused into three different nephron segments: early proximal, late proximal and early distal sites with or without nisoldipine. Calcium efflux averaged 93.6 +/- 4.9 and 90.5 +/- 8.7% after early and late proximal administration, respectively, indicating that the proximal tubule and the loop of Henle are highly efficient in transporting calcium out of the tubule. In distal nephron segments, calcium transport was limited to 41.1 +/- 4.8% of the amount delivered to these tubules. Nisoldipine inhibited the efflux of simultaneously infused calcium. This apparent inhibitory effect occurred predominantly in distal nephron segments where the drug reduced calcium efflux from 41.1 +/- 4.8 to 22.5 +/- 2.7%, indicating a 45.3% reduction in net calcium reabsorption. The results are consistent with the interpretation that nisoldipine-induced reduction in the tubular efflux of calcium was secondary to a direct inhibition of voltage-sensitive, L-type calcium channels or to a blunting of the rate of phosphorylation of channel proteins by protein kinase C in the distal tubular epithelial cells.     

Anatomy and ultrastructure of the excretory system of the lizard, Sceloporus cyanogenys

The anatomy and ultrastructure of the lizard kidney (Sceloporus cyanogenys) have been studied by light and electron microscopy. The number of glomeruli was counted in serial sections and estimated to be 2,000 (in the two kidneys). Beginning with the glomerulus and Bowman's capsule the nephron segments are sequentially: (a) proximal tubule; (b) intermediate ciliated segment consisting of a proximal and distal part; (c) distal tubule, which can be divided into two segments, followed by (d) connecting tubule and (e) initial collecting duct. The initial collecting ducts from several nephrons open into the collecting duct. Tubular epithelium in this lizard has similarities to that of other reptiles. The lateral borders do not overlap like in mammals, but interdigitate by fingerlike projections. The length of the nephron segments was measured in disected tubules and the diameter was measured on light and electron micrographs. From these measurements estimates of inner tubular surface area were made. Together with data from physiological studies (Stolte et al., '76; Schmidt-Nielsen, '76) the estimated surface area was used to calculate transport rates per unit area across the epithelium. Comparisons of structure and transport rates per unit area across the epithelium. Comparisons of structure and transport rates were made between S. cyanogenys and other reptiles and mammals.     

Dystrophin and Dp140 in the adult rodent kidney

Full-length dystrophin and a truncated carboxy-terminal isoform, Dp140, also encoded by the dystrophin gene, are expressed in rodent kidney. Dystrophin is localized to the vascular smooth muscle and mesangial cells. Dp140 was initially identified in the brain as well as kidney. In kidney, Dp140 is localized to the basal surface of tubule epithelial cells. Morphology and double-labeling suggest that it is restricted to the ascending loop of Henle, distal convoluted tubule, and proximal end of the collecting ducts. Because both dystrophin and Dp140 contain the same carboxy-terminal domain--which in skeletal muscle forms a link to integral membrane proteins and in turn to the extracellular matrix--Dp140 in the tubule epithelium might contribute to anchoring the basal aspect of the cells to the basement membrane. The identification of dystrophin gene products in kidney parenchyma also raises the possibility of subtle renal abnormalities, not previously suspected, as part of the Duchenne muscular dystrophy phenotype.     

Induction of rabbit renal mixed-function oxidases by phenobarbital: cell specific ultrastructural changes in the proximal tubule

Administration of phenobarbital (60 mg/kg) daily for 4 days to male rabbits resulted in induction of renal cytochrome P-450 (3.5-fold) and a corresponding increase in ethoxycoumarin-O-deethylase and benzphetamine-N-demethylase activity (17- and 4-fold, respectively). Kidney weight to body weight ratio and renal ethoxyresorufin-O-deethylase were not affected by phenobarbital pretreatment. Numerous focal areas of proliferation of smooth endoplasmic reticulum (SER) were evident in proximal tubule cells from phenobarbital treated rabbits while proximal tubular cells from control rabbits had only small and sparcely located aggregates of SER. Phenobarbital-induced SER proliferation was specifically localized to the S3 segment of the proximal tubule. Proliferation was not observed in S2 cells of the proximal tubule, cells of Henle's loop, distal tubules, or collecting tubules in rabbits pretreated with phenobarbital. These data demonstrate the biochemical heterogeneity of cell types within the proximal tubules of rabbits. Furthermore, induction of mixed-function oxidases specifically in S3 cells of the proximal tubule may be of toxicological significance in the metabolic activation of certain nephrotoxicants.     

Spiral structures in the wall of the hepatic venous system in the dog

Unique spiral structures, located in the wall of the hepatic venous system in the dog, were examined in the central veins and the hepatic venous branches, utilizing microvascular corrosion casting and freeze-fracture technique in scanning electron microscopy and transmission electron microscopy of tissue sections. The whole hepatic venous system was divided into 4 portions: the central, sublobular, collecting and branches of the hepatic veins. The central vein was spindle-shaped with several compressions. Removing the endothelial cells of the central vein, pathways of venous sinusoids were like a labyrinth. In the sublobular veins, spiral structures distinctly appeared as the diameter increased. Beneath the endothelial cells in the constricted portions, smooth muscle bundles were found. The spiral structures gradually became irregular in the collecting veins and discontinuous to form shallow constrictions in cast thicker branches of the intrahepatic veins. A single, fine spindle of the central vein was formed by the arrangement of liver cells. The spiral structures of the sublobular vein were formed by smooth muscle bundles. Irregularity of the spiral structures in the collecting veins was caused by smooth muscle bundles anastomosing with adjacent ones. Disappearance of the spiral structure in cast thicker branches of the intrahepatic veins was due to absence of muscle bundles.     

Magnesium homeostasis and renal magnesium handling

Magnesium is essentially an intracellular cation, which makes it difficult to evaluate magnesium status. About 1% of total body magnesium is present in serum and interstitial body fluid and only about 1% of the intracellular magnesium is in the free form, Mg2+. Recent studies show that this small fraction of free Mg2+ rapidly changes with the extracellular magnesium. These free Mg2+ levels are carefully controlled within the cell and total cellular magnesium content are maintained at the expense of extracellular fluid and bone magnesium levels. Regulation of magnesium balance is met between intestinal absorption and renal excretion. The excretory side of magnesium balance involves appropriate changes in renal magnesium handling. Present evidence indicates that renal handling of magnesium normally is a filtration-reabsorption process; magnesium is filtered at the glomerulus and reabsorbed along the various segments making up the renal nephron. About 80% of total serum magnesium (0.7-1 mmol/l) is filtered at the glomerular membrane. Of the ultrafilterable magnesium (0.6-0.8 mmol/l) 20-25% is reabsorbed by the proximal tubule, including the convoluted and straight portions. Some 50-60% of the filtered magnesium is reabsorbed in the loop of Henle, specifically by thick ascending limb cells. The terminal nephron segments, including the distal convoluted tubule and collecting ducts, reabsorb only a small portion of the filtered magnesium (about 5-10%). The loop of Henle plays the major role in determining magnesium reabsorption and urinary magnesium excretion. The loop of Henle also is the segment in which the major regulatory factors act to maintain magnesium balance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of two arginase isoenzyme activities along the nephron of Meriones shawi

Conflicting theories on the existence of several renal arginase isoenzymes remain in debate. Because the activity of arginase is high in two embryologically different nephron segments of the Meriones shawi kidney, namely the cortical (CPST) and medullary (OSPST) proximal straight tubule and the outer medullary collecting duct (OMCD), we postulate that these nephron segments may contain different isoforms. Isolated nephron segments were dissected from collagenase-treated kidneys. Tubules were permeabilized with Triton X-100 (0.25%) and incubated with increasing Arg concentrations to characterize the arginase activity. The results were as follows: (1) in OMCD, one arginase isoform (E1), characterized by a high Arg affinity (1.160 mM), was present; (2) in CPST, two arginase isoforms were discovered - one, E1, had a similar Km (1.407 mM) to that found in OMCD whereas the other (E2) had a low affinity for Arg (Km =18.8 mM); and (3) in OSPST, two isoenzymes were present - E1 which had a Km of 1.478 mM and the second isoform that we named E2 which had a Km of 9.07 mM. In addition, arginase located in CPST and OMCD was strongly inhibited by Orn and Lys. The Ki value for Lys varied between 1.635 and 2.288 mM. Therefore, this work demonstrates that two arginase isoforms are present in the kidney of Meriones shawi. Isoform E1 is present in the proximal tubule and the collecting duct whereas isoform E2 is restricted to the proximal tubule.     

Central venous catheter failure is induced by injury and can be prevented by stabilizing the catheter tip

PURPOSE: Thrombosis associated with central venous catheters is a significant cause of device failure, morbidity, and loss of access sites. We hypothesized that central vein thrombosis is caused by catheter injury to the vein wall and that it can be reduced by stabilizing the catheter tip. To test these hypotheses, we studied central vein catheters in a porcine model. Test catheters had a silicone-encased stainless steel loop at the indwelling end that contacted the vein wall and stabilized the catheter tip in the center of the vessel. METHODS: Sealed silicon elastic (Silastic) catheters (3.2 mm outer diameter) with and without a stabilizing loop were inserted via the external jugular vein into the superior vena cava just above the right atrium. Animals were killed at 1, 2, 4, and 8 weeks, and the vena cava was inspected for the presence of thrombus and entrapment of the catheter tip. RESULTS: In control animals mural thrombus developed at the site of the catheter tip. This thrombus organized by invasion of macrophages and smooth muscle cells, eventually forming a lesion similar to intimal hyperplasia. Lesion cross-sectional area was significantly smaller in animals with loop catheters than in control animals at 2 weeks (1.2 +/- 1.3 vs 34.5 +/- 23.9 mm2; p = 0.05) and 4 weeks (2.8 +/- 0.3 vs 13.9 +/- 5.8 mm2; p < 0.05). By 8 weeks the vena cava was nearly occluded in most animals and the catheter tip was entrapped in this lesion in all cases. Test catheters eliminated the injury process for up to 8 weeks (p < 0.01, chi2 control vs loop catheter entrapment). Very little injury response was found where the loop contacted the vein wall, and the catheter tip was free of thrombus in all cases. CONCLUSIONS: Mural thrombosis at the tip of indwelling central catheters is caused by chronic mechanical venous wall injury. Vessel injury and the resulting thrombosis can be prevented by a catheter modification that stabilizes the tip. Such a catheter may significantly reduce catheter malfunction and morbidity associated with these devices.     

Immunolocalization of phospholipase C isoforms in rat kidney

BACKGROUND: Phospholipase C (PLC) is an important factor in signal transduction because this enzyme is activated by several hormones and growth factors. Eight PLC isoforms have been described raising the possibility that different cells express a single isoform or activate specific isoforms in different cells. Therefore, the goal of this study was to determine which PLC isoforms are expressed in specific regions of rat kidney. METHODS: Western blot analysis was performed in microdissected nephron segments of rat kidney, while immunohistochemical analysis was performed on whole rat kidney slices using PLC isoform-specific antibodies. RESULTS: All three families of PLC isoforms (beta, gamma, and delta) were present throughout the cortical and medullary regions of the kidney. Only the PLC-beta1 isoform was observed in the brush border of the proximal tubule, but all isoforms were present in glomeruli and in the cytoplasm of tubular epithelial cells. In addition, only the PLC-gamma1 isoform was expressed in the internal elastic lamina of the renal artery, while vasa recta expressed PLC-beta1 most intensely. Medullary thick ascending limbs showed an intense level of expression of all three isoforms. CONCLUSION: Multiple PLC isoforms are present in glomeruli, renal tubules, and renal vasculature in vivo, but with some segment-specific differences. These findings suggest that the response of a specific cell is not determined by expression of only one PLC isoform, with the exception of the brush border of the proximal tubule and the renal arteries. Instead, the presence of multiple PLC isoforms in specific regions of the kidney suggests that hormonal regulation in vivo involves mechanisms beyond cell-specific isoforms of PLC.     

Intra-renal and subcellular distribution of the human chloride channel, CLC-5, reveals a pathophysiological basis for Dent's disease

Dent's disease, which is a renal tubular disorder characterized by low molecular weight proteinuria, hypercalciuria and nephrolithiasis, is associated with inactivating mutations of the X-linked chloride channel, CLC-5. However, the manner in which a functional loss of CLC-5 leads to such diverse renal abnormalities remains to be defined. In order to elucidate this, we performed studies to determine the segmental expression of CLC-5 in the human kidney and to define its intracellular distribution. We raised and characterized antisera against human CLC-5, and identified by immunoblotting an 83 kDa band corresponding to CLC-5 in human kidney cortex and medulla. Immunohistochemistry revealed CLC-5 expression in the epithelial cells lining the proximal tubules and the thick ascending limbs of Henle's loop, and in intercalated cells of the collecting ducts. Studies of subcellular human kidney fractions established that CLC-5 distribution was associated best with that of Rab4, which is a marker of recycling early endosomes. In addition, confocal microscopy studies using the proximal tubular cell model of opossum kidney cells, which endogenously expressed CLC-5, revealed that CLC-5 co-localized with the albumin-containing endocytic vesicles that form part of the receptor-mediated endocytic pathway. Thus, CLC-5 is expressed at multiple sites in the human nephron and is likely to have a role in the receptor-mediated endocytic pathway. Furthermore, the functional loss of CLC-5 in the proximal tubules and the thick ascending limbs provides an explanation for the occurrences of low molecular weight proteinuria and hypercalciuria, respectively. These results help to elucidate further the patho-physiological basis of the renal tubular defects of Dent's disease.     

Familial renal tubular dysgenesis: a disorder not isolated to proximal convoluted tubules

The autopsy findings of a newborn with renal tubular dysgenesis, born to first cousins of Moslim Arab descent, are described. Hypocalvaria and hyperflexible joints were noted in addition to the renal lesion. A microdissection study demonstrated marked shortening of all the nephron segments from the glomeruli to the collecting tubules, rather than an isolated abnormality of the proximal convoluted tubules.     

Murine autosomal recessive polycystic kidney disease with multiorgan involvement induced by the cpk gene

BACKGROUND: Autosomal recessive (AR) polycystic kidney disease (PKD) is characterized in humans and mice as a rapidly progressive, collecting duct cystic disease usually leading to uremia in the neonatal or infantile period. In humans, ARPKD renal pathology can be variable in severity and is associated with the development of prominent bile duct and liver pathology. The C57BL/6J-cpk/cpk mouse model of ARPKD is the most extensively studied murine model of inherited infantile PKD; however, these mice lack extrarenal pathology. METHODS: In the present study, the cpk gene was backbreed onto CD1 mice to examine the development of cpk-induced ARPKD in this outbred mouse background. Resulting cystic offspring were examined morphologically and their serum urea nitrogen levels were assessed. RESULTS: The rapid development of PKD in CD1 mice homozygous for the cpk gene appears to be slightly more rapid but otherwise comparable to that seen in inbred C57BL/6J mice. In CD1-cpk/cpk mice, the principal renal pathological finding is collecting duct cysts, which are lined by a relatively uniform epithelium. This epithelium appears to be relatively undifferentiated based on almost total absence of intercalated cells. Proximal tubule cysts are prominent in the first postnatal week while collecting duct cysts predominate in the later stages of the disease. Extrarenal manifestations of the cpk gene are evident in the CD1 strain and include cysts of pancreatic, common bile, and major hepatic ducts. Intrahepatic bile ducts also have focal dilations. Primary (thymus) and secondary (spleen) lymphoid tissues become hypoplastic as azotemia progresses. The strain-related variability in renal and liver changes in cpk-induced ARPKD may reflect the influence of other genes (possibly modifier genes) expressed in this mouse strain. In older CD1-cpk/+ mice, renal (proximal tubular) cysts and prominent liver cysts (lined by a biliary epithelium) develop, indicating that the heterozygous state (cpk/+ genotype) causes renal and hepatic pathology. CONCLUSIONS: The cpk gene, when placed on an appropriate mouse strain background, causes multiorgan disease that more closely mimics human ARPKD than when the cpk gene is expressed on the C57BL/6J strain. A gene dose effect is present as cystic pathology is present in kidney and liver of both suckling homozygous (cpk/cpk) and old heterozygous (cpk/+) mice.     

Effect of renal sympathetic nerve stimulation on proximal water and sodium reabsorption

The renal responses to sympathetic nerve stimulation were studied in saline-expanded rats. The left kidney was partially denervated by crushing the left greater splanchnic nerve. Then the distal portion of the nerve was stimulated with square wave pulses of 0.5 ms duration, voltage twice threshold, and 1 or 2 Hz frequency while monitoring the compound action potential. Fibers with conduction speeds of 13-17 m-s-1 and of 0.7-1 m-s-1 were identified. Only stimulation of the latter appeared to produce changes in renal Na and water excretion. Whole kidney and individual nephron studies were performed alternating control and nerve stimulation periods. Nerve stimulation produced approximately a 25% reduction of the left kidney urine volume and sodium excretion. Glomerular filtration rate and renal plasma flow remained unchanged. Right kidney Na and water excretion, glomerular filtration rate, and renal plasma flow remained constant. In the left kidney, during nerve stimulation, the tubular fluid to plasma inulin concentration ratio increased significantly in the late proximal tubule. We conclude that the antidiuresis and antinatriuresis seen during sympathetic nerve stimulation were caused by increased sodium and water reabsorption in the proximal tubule, probably mediated by the stimulation of slowly conducting unmyelinated fibers. These responses appeared to be unrelated to systemic or intrarenal hemodynamic changes.