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Glycerophosphorylcholine (GPC), sorbitol and inositol were quantitated in renal tubule suspensions from inner and outer medulla of untreated Sprague-Dawley rats to study the regulation of organic osmolyte concentrations under different metabolic conditions and varying extracellular osmolalities in vitro. Inner medullary tubules prepared in hypertonic saline (550 mosm/kg) contained osmolyte concentrations comparable to those found in the kidney in vivo. Incubation for up to 8 h at 5 mmol/l glucose increased sorbitol in the inner medullary tubules and medium in an osmolality-dependent fashion, whereas GPC and inositol remained constant. At a given glucose concentration the rate of sorbitol formation decreased linearly with increasing tubular sorbitol concentration, which was regulated by an osmolality-dependent export mechanism. Perturbation of tubular mechanisms by inhibition of glycolysis or oxidative phosphorylation did not change the tubular osmolyte content. In contrast to papilla outer medullary tubules contained only inositol. Lactate added as a metabolic substrate to the outer medullary tubules did not change the cellular inositol levels. In outer medullary tubules osmolality changes (320-710 mosm/kg) had no effect on tubular inositol. Addition of furosemide was without effect, when added in vitro. The results indicate that tubular sorbitol formation is regulated by glucose concentration, the level of tubular sorbitol, and an osmolality-dependent export mechanism. In contrast, cellular inositol and GPC levels seem to be independent of acute changes in tubular metabolism. 相似文献
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Layton AT Gilbert RL Pannabecker TL 《American journal of physiology. Renal physiology》2012,302(7):F830-F839
Recent anatomic findings indicate that in the upper inner medulla of the rodent kidney, tubules, and vessels are organized around clusters of collecting ducts (CDs). Within CD clusters, CDs and some of the ascending vasa recta (AVR) and ascending thin limbs (ATLs), when viewed in transverse sections, form interstitial nodal spaces, which are arrayed at structured intervals throughout the inner medulla. These spaces, or microdomains, are bordered on one side by a single CD, on the opposite side by one or more ATLs, and on the other two sides by AVR. To study the interactions among these CDs, ATLs, and AVR, we have developed a mathematical compartment model, which simulates steady-state solute exchange through the microdomain at a given inner medullary level. Fluid in all compartments contains Na(+), Cl(-), urea and, in the microdomain, negative fixed charges that represent macromolecules (e.g., hyaluronan) balanced by Na(+). Fluid entry into AVR is assumed to be driven by hydraulic and oncotic pressures. Model results suggest that the isolated microdomains facilitate solute and fluid mixing among the CDs, ATLs, and AVR, promote water withdrawal from CDs, and consequently may play an important role in generating the inner medullary osmotic gradient. 相似文献
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A model of countercurrent exchange has been developed to simulate transport of salt, urea and water among vasa recta and descending
limbs of the loop of Henle in the inner medulla. These vessels are abstracted as three concentric cylinders: the inne one
represents descending vasa recta, the middle one represents ascending vasa recta and the outer one represents descending limbs.
The capillary plexus, which connects the ascending and descending vasa recta, is modeled as a series of well-mixe compartments.
Multicomponent transport equations for the sytem are derived from steady state mass balances and simple passive flux relations.
The resulting set of nonlinear equations are solved numerically by an iterative Gauss-Seidel algorithm with under-relaxation.
Simulations yield the salt and urea concentrations as well as volume flow rates in all tubes and compartments. The simulations
indicate that solute concentrations can increase monotonically toward the papillae even if all transport processes within
the exchanger are passive and source fluxes decrease monotonically toward the papillae. 相似文献
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The present study was designed to investigate the effect of dexamethasone treatment for 2 weeks (2.5 mg/kg/week, subcutaneously) on the level of unesterified fatty acids, particularly arachidonic acid, in the renal medulla of rats, and to relate the observed effect to changes in the tissue concentration and the fatty acid composition of renal medulla phospholipids and triglycerides. Dexamethasone treatment caused an increase in the renal inner medulla level of unesterified fatty acids, including arachidonic acid, that was associated with a reduction of triglycerides and of arachidonic acid esterified into triglycerides, and with an increase in the rate of fatty acids esterification into triglycerides. In contrast, dexamethasone treatment did not affect the renal medulla concentration of phospholipids, the arachidonic acid content of renal medulla phospholipids, or the rate of esterification of fatty acids into renal medulla phospholipids. In the face of increased fatty acid esterification into triglycerides, the finding of reduced triglyceride levels in the renal medulla of dexamethasone-treated rats suggests excessive triglyceride breakdown. If so, fatty acids including arachidonic acid liberated from triglycerides may contribute to elevation of unesterified fatty acid levels in the renal medulla during dexamethasone treatment. The increased level of free arachidonic acid in the renal medulla of dexamethasone-treated rats may explain in part the reported effect of this steroid in increasing urinary prostaglandins. 相似文献
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Khegaĭ II 《Rossi?skii fiziologicheski? zhurnal imeni I.M. Sechenova / Rossi?skaia akademiia nauk》2004,90(12):1563-1566
A western-blot analysis using monoclonal antibodies revealed that a reduction of alpha-actinin occurred in the renal inner medulla under the long-lasting dehydration. The ratio between protein content measured in rats of WAG line being hydrated or after 3-days water deprivation consisted of 52.7+/-6.2 against 23.9+/-3.3 as evaluated in relative units. The alpha-actinin level changes similarly in mutant rats of Brattleboro line not capable of synthesizing vasopressin. It was 57.5+/-4.6 in hydrated animals, and statistically lower in rats being under 3-day water deprivation--26.4+/-5.7 in relative units of protein. 相似文献
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Incorporation of [32P]orthophosphate into phosphatidylcholine, lysophosphatidylcholine and molecular species of phosphatidylcholine in vivo was observed in liver, plasma and erythrocytes of bile duct-ligated or sham-operated rats. Both the amount and radioactivity of dienoic species of phosphatidylcholine in all tissues examined increased in bile duct-ligated rats as compared to sham-operated rats. The experiments in vivo and in vitro showed that the ratio of lysophosphatidylcholine to phosphatidylcholine transferred to erythrocytes from plasma in sham-operated rats was much higher than that in bile duct-ligated rats. It is suggested that one of the mechanisms by which abnormal erythrocytes appear might be explained by the facilitated and direct transfer of phosphatidylcholine, which is caused by the interaction of erythrocytes with bile acid in bile duct-ligated rat plasma. 相似文献
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Vilbig RL Sarkar A Zischkau J Knepper MA Pisitkun T 《American journal of physiology. Renal physiology》2012,303(3):F366-F372
Concentrating models of the renal inner medulla can be classified according to external free-energy balance into passive models (positive values) and models that require an external energy source (negative values). Here we introduce an online computational tool that implements the equations of Stephenson and colleagues (Stephenson JL, Tewarson RP, Mejia R. Proc Natl Acad Sci USA 71: 1618-1622, 1974) to calculate external free-energy balance at steady state for the inner medulla (http://helixweb.nih.gov/ESBL/FreeEnergy). Here "external free-energy balance" means the sum of free-energy flows in all streams entering and leaving the inner medulla. The program first assures steady-state mass balance for all components and then tallies net external free-energy balance for the selected flow conditions. Its use is illustrated by calculating external free-energy balance for an example of the passive concentrating model taken from the original paper by Kokko and Rector (Kokko JP, Rector FC Jr. Kidney Int 2: 214-223, 1972). 相似文献
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E J Neer 《The Journal of biological chemistry》1973,248(13):4775-4781
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F Ikemoto G B Song M Tominaga Y Kanayama K Yamamoto 《Biochemical and biophysical research communications》1987,144(2):915-921
Regional distribution of angiotensin converting enzyme(ACE) in the rat kidney was studied. The ACE activities in the inner cortex and outer medulla were about 10 and 5 times those in the outer cortex, respectively. The activity in the inner medulla or papilla was much the same as that in the outer cortex. Immunofluorescence was greatest in the proximal tubules in the inner cortex, while the outer medulla and the inner medulla or papilla showed a weak fluorescence. The brush border membranes isolated from the inner cortex also possessed about 10 times the ACE activity seen in the outer cortex. The results indicate that the major source of renal ACE is not the proximal convoluted tubules in the outer cortex, but rather the brush border membranes of proximal tubules in the inner cortex. The contribution of ACE in the inner cortex would therefore be predominant. 相似文献
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1. In rat kidney cortex, outer and inner medulla the development of activities of seven enzymes was investigated during postnatal ontogeny (10, 20, 30, 60 and 90 days of age). The enzymes were selected in such a manner, as to characterize most of the main metabolic pathways of energy supplying metabolism: hexokinase (glucose phosphorylation, HK), glycerol-3-phosphate dehydrogenase (glycerolphosphate metabolism or shunt, GPDH), triose phosphate dehydrogenase (glycolytic carbohydrate breakdown, TPDH), lactate dehydrogenase (lactate metabolism, LDH), citrate synthase (tricarboxylic acid cycle, aerobic metabolism, CS), malate NAD dehydrogenase (tricarboxylic acid cycle, intra-extra mitochondrial hydrogen transport, MDH) and 3-hydroxyacyl-CoA-dehydrogenase (fatty acid catabolism, HOADH). 2. The renal cortex already differs metabolically from the medullar structures on the 10th day of life. It displays a high activity of aerobic breakdown of both fatty acids and carbohydrates. Its metabolic capacity further increases up to the 30th day of life. 3. The outer medullar structure is not grossly different from the inner medulla on the 10th day of life. Further it differentiates into a highly aerobic tissue mainly able to utilize carbohydrates. It can, however, to some extent, also utilize fatty acids aerobically and produce lactate from carbohydrates anaerobically. 4. The inner medullar structure is best equipped to utilize carbohydrates by anaerobic glycolysis, forming lactate. This feature is already pronounced on the 10th day of life, its capacity increases to some extent during postnatal development, being highest between the 10th and the 60th day of life. 相似文献
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Frederick R. Derubertis Patricia A. Craven 《Biochimica et Biophysica Acta (BBA)/General Subjects》1979,585(4):499-511
Studies of the chromatographic distribution of soluble protein kinase in rat kidney demonstrated that the type I isoenzyme predominates in cortex, whereas activity in outer and inner medulla is almost exclusively the type II form. The type II isoenzyme also predominates (95% or greater) in human, canine, bovine, porcine and rabbit inner medulla. Compared to soluble type I activities from rat renal cortex or medulla, type II activity of inner medulla demonstrates a marked resistance to activation by NaCl and/or urea in subcellular preparations. However, with respect to solute activation, the resistance of the type II enzyme of inner medulla does not differ from that of type II activities from other tissues. In contrast to the effects on basal activity, NaCl and urea potentiated inner medullary type II activation by cyclic AMP and also delayed the rate of subunit reassociation after chromatographic removal of cyclic AMP. Incubation of inner medullary slices in high osmolality buffer (NaCl and urea) did not alone activate soluble protein kinase, an observation which implied that the enzyme was also resistant to solute activation in the intact cell system. Moreover, at 1650 mosM, vasopressin activation of soluble protein kinase was enhanced compared to responses at 750 mosM despite comparabel levels of cyclic AMP accumulation at the two osmolalities. However, a cyclic AMP-independent action of high osmolality to reduce the rate of inactivation of arginine vasopressin-stimulated protein kinase was not demonstrable in inner medullary slices.The present data suggest the possibility that the resistance of inner medullary protein kinase to solute activation could be related to the isomeric form of enzyme (type II) present in this tissue. The high concentrations of NaCl and urea routinely found in inner medulla during hydropenia also influenced protein kinase responses to arginine vasopressin, and may do so in part by directly potentiating the action of cyclic AMP on subunit dissociation. 相似文献
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M Dubois G Némoz M Lagarde A F Prigent 《Biochemical and biophysical research communications》1990,170(2):800-809
Cyclic nucleotide phosphodiesterase activity in rat heart microsomes is attributable to several isoenzymatic forms: a cyclic AMP-specific, a cyclic GMP-specific, and a cyclic GMP-stimulated enzyme. Incubation of microsomes with an exogenous phospholipase C (C. welchii) induced a marked stimulation (+126%) of cyclic AMP phosphodiesterase and a moderate stimulation (+49%) of cyclic GMP-phosphodiesterase in the membrane-bound fraction. Besides, a notable fraction of activity was solubilized by the treatment. A parallel decrease in the activating effect of cyclic GMP on the hydrolysis of cyclic AMP was observed in the membranes (down to 18% of the control effect). It resulted from a marked stimulation of the basal activity, while the activated level was unaffected. The treatment by an exogenous phospholipase D induced more moderate modifications. The addition to microsomes of oleyl,acetyl-glycerol, but not of long chain-diacylglycerols, partly reproduced the phospholipase C effect. Phosphatidate also induced variations in phosphodiesterase activity, and could thus participate in the phospholipase effects. These results suggest that endogenous phospholipases, the activity of which is modulated by hormonal stimuli, might influence phosphodiesterase activity in cardiac membranes by producing phospholipid metabolites, with potential consequences on heart contractility. 相似文献