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C Lechene

Publications and source records attributed to C Lechene.

72 records · Page 4Linked to original sources
PubMed1981

Sodium orthovanadate diuresis in rats.

The renal actions of differing doses of sodium orthovanadate were studied in conscious and anesthetized female Wistar rats. In conscious rats, sodium orthovanadate was given by i.v. or i.p. injections or by mouth. The most pronounced renal effects were seen after a 5 mg/kg i.p. injection of sodium orthovanadate. Urine flow and sodium excretion increased approximately 400% and urine osmolality fell from 1108 to 549 mOsmol/kg . H2O. Higher doses of sodium orthovanadate (20, 30 and 50 mg/kg) injected i.p. did not cause diuresis and were toxic. In anesthetized rats undergoing a 0.9% NaCl diuresis, i.v. infusion of sodium orthovanadate at a dose of 5 mg/kg/hr significantly increased urine flow and the excretion of sodium, calcium, phosphorus, sulfur, magnesium and chlorine, whereas glomerular filtration rate was unaltered. In anesthetized rats undergoing a water diuresis, i.v. infusion of sodium orthovanadate (5 mg/kg/hr) markedly reduced free-water clearance, indicating that this compound inhibits tubular reabsorption of sodium and chloride in diluting nephron segments. Blood and renal tissue levels of vanadium, measured using emission spectrographic analysis, in rats infused with sodium orthovanadate were 4 times higher than the concentration of sodium orthovanadate (1--10 microM) needed to inhibit 50% of the Na-K-adenosine triphosphate activity of rat renal homogenates in vitro. These data suggest that sodium orthovanadate produces diuresis at least in part by inhibiting Na-K-adenosine triphosphatase and solute transport in the distal nephron, likely the ascending limb of the loop of Henle.

Administration, Oral↗
PubMed1980

Isosmotic volume reabsorption in rat proximal tubule.

A theoretical model incorporation both active and passive forces has been developed for fluid reabsorption from split oil droplets in rat intermediate and late proximal tubule. Of necessity, simplifying assumptions have been introduced; we have assumed that the epithelium can be treated as a single membrane and that the membrane "effective" HCO3 permeability is near zero. Based on this model with its underlying assumptions, the following conclusions are drawn. Regardless of the presence or absence of active NaCl transport, fluid reabsorption from the split oil droplet is isosmotic. The reabsorbate osmolarity can be affected by changes in tubular permeability parameters and applied forces but is not readily altered from an osmolarity essentially equal to that of plasma. In a split droplet, isosmotic flow need not be a special consequence of active Na transport, is not the result of a particular set of permeability properties, and is not merely a trivial consequence of a very high hydraulic conductivity; isosmotic flow can be obtained with hydraulic conductivity nearly an order of magnitude lower than that previously measured in the rat proximal convoluted tubule. Isosmotic reabsorption is, in part, the result of the interdependence of salt and water flows, their changing in parallel, and thus their ratio, the reabsorbate concentration being relatively invariant. Active NaCl transport can cause osmotic water flow by reducing the luminal fluid osmolarity. In the presence of passive forces the luminal fluid can be hypertonic to plasma, and active NaCl transport can still exert its osmotic effect on volume flow. There are two passive forces for volume flow: the Cl gradient and the difference in effective osmotic pressure; they have an approximately equivalent effect on volume flow. Experimentally, we have measured volume changes in a droplet made hyperosmotic by the addition of 50 mM NaCl; the experimental results are predicted reasonably well by our theoretical model.

Animals↗
PubMed1980

Sodium and chloride transport along the inner medullary collecting duct: effect of saline expansion.

The effect of volume expansion on inner medullary collecting duct (IMCD) sodium transport remains controversial. Studies employing micropuncture of the IMCD base and tip were interpreted to demonstrate enhanced sodium and chloride reabsorption. Data obtained by microcatheterization evaluating only sodium transport revealed either no reabsorption or net addition. We have examined both sodium and chloride transport by microcatheterization. Volume expansion was comparable to the micropuncture studies: 0.9% saline equal to 10% body wt and then matched to urine flow. The fraction of filtered fluid, sodium, and chloride was analyzed as a function of IMCD length. In eight hydropenic rats 60% of the fluid, 71% of the sodium, and 48% of the chloride delivered to the IMCD was reabsorbed. In six volume-expanded rats no significant net reabsorption of fluid, sodium, or chloride was found. Accordingly, in contrast to the micropuncture results, we have demonstrated that net sodium chloride and fluid reabsorption are absent during volume expansion. We conclude that during volume expansion, fluid, sodium, and chloride excretion increase, in part, because of a reduction in net reabsorption along the IMCD. The degree of volume expansion does not account for the discrepancy between the two techniques.

Adsorption↗
PubMed1980

Renal medullary concentrating process: an integrative hypothesis.

The inability to demonstrate adequate active transport in the ascending thin limb of the mammalian kidney has led to the development of models of concentration with only passive transport in the inner medullary loop of Henle. These models depend on very limited solute entry into the descending thin limb, an assumption counter to much of the experimental in vivo data. In addition, these models have not incorporated the vascular-tubular relationships in the renal medulla. We hypothesize that fluid enters the inner medulla in the descending thin limb slightly hyperosmotic to the fluid leaving the inner medulla in the interstitial-vasa recta compartment. We illustrate the hypothesis with a steady-state model of the medullary concentration process with no active transport in the inner medullary loop of Henle and with tubular permeability properties and solute concentrations consistent with experimental data. A difference of 33 mosmol/kg between descending thin limb and fluid leaving the inner medulla in the interstitial-vasa recta compartment results in an increase in formative urine osmolality from 530 mosmol/kg in the collecting duct at the outer-inner medullary boundary to 2,200 mosmol/kg in the ureteral urine. The hypothesis incorporates anatomical and physiological properties of the vascular and tubular structures in the outer medulla.

Animals↗
PubMed1980

Effect of urea concentration of pelvic fluid on renal concentrating ability.

The role of the pelvic urine in the renal concentration process was examined in anesthetized antidiuretic rats. The left ureter was cannulated with perfusion and collection catheters so that the composition of the fluid bathing the papilla could be altered by superperfusing solution of known composition without opening the renal pelvis, exposing the papilla, or altering intrapelvic pressure. The effect on urinary osmotic pressure (Uosmol) of papillary superperfusion with solutions of varying urea concentrations and total osmolality was examined. Papillary superperfusion with solutions containing no urea or less urea than preperfusion pelvic urine caused marked reductions in Uosmol regardless of the osmotic pressure of the solution. Superperfusion solutions with urea concentrations similar to that of preperfusion pelvic urine but lower in osmotic pressure than preperfusion urine produced no change in Uosmol. Superperfusion solutions with urea concentrations higher than that of preperfusion urine and with osmotic pressure equal to that of the preperfusion urine increased Uosmol. Finally, superperfusion of the papilla with urea solutions of greater than 2,370 mosmol/kg H2O and hypertonic to preperfusion urine decreased Uosmol. We conclude that the urea concentration of the pelvic urine plays an essential role in the urinary concentration mechanism.

Animals↗
PubMed1980

Electron probe microanalysis of biological soft tissues: principle and technique.

Electron probe microanalysis is a method based upon X-ray spectrometry used for analyzing the chemical element content of very small amounts of material. The concentration of electrolytes in the microenvironment of cells, in cells, and in intracellular organelles can be measured. The main difficulties in using this method in biological soft tissue lie in sample preparation and in proper interpretation of the data. Best tissue preparation seems to be to quench the sample and to analyze it either freeze dried in thin or ultrathin sections, or frozen hydrated in thin sections or bulk samples. In all cases analysis should be performed using a cold stage and an ultra clean vacuum in order to minimize mass loss due to beam damage and mass gain due to contamination trapping. Interpretation of the data relies upon the knowledge of both the localization of the volume excited by the electron beam and the origin of the continuum and characteristic X-ray signals received by the X-ray spectrometer. This knowledge can be complicated by two facts: 1) when the electron beam is used in an analytical mode, viewing of the analyzed microarea can be lost, and 2) the X-ray signals received by the spectrometer can originate not only from the volume directly excited by the electron beam but from areas that can be far apart, excited by the electron beam tail, scattered electrons or secondary fluorescence, particularly when using energy dispersive spectrometers. Theoretical quantitation of the results is well developed. Practical quantitation could be complicated by the possibility of mass gain, mass loss, standard inhomogeneity, non-uniformity of sample thickness, possibility of shrinkage during freeze drying and, when using energy dispersive spectrometry, by the low signal over background for low atomic number elements (Na), the possibility of overlap of characteristic X-ray lines, and the use of complex and empirical methods for background stripping and peak deconvolution. All these difficulties can be overcome, making electron probe microanalysis one of the most powerful tools available to the biologist.

Animals↗
PubMed1977

Vanadate is a potent (Na,K)-ATPase inhibitor found in ATP derived from muscle.

A potent (Na,K)-ATPase inhibitor purified from "Sigma Grade* ATP has been identified as vanadium using electron probe microanalysis and confirmed by microwave-induced emission spectroscopy and electron paramagnetic resonance spectroscopy. Sodium orthovanadate (Na3 VO4) is identical with the purified inhibitor with respect to ultraviolet absorbance, migration on thin layer chromatography, and inhibition of (Na,K)-ATPase. The (Na,K)-ATPase is in-inhibited 50% by 40 nM Na3 VO4 under optimal conditions (28 mM Mg2+) and the inhibition is 100% reversible by millimolar concentrations of norepinephrine. The physiological significance of this inhibition is discussed in relation to vanadium concentrations in vivo.

Adenosine Triphosphatases↗
PubMed1977

Renal tubule ion transport and collecting duct function in the elasmobranch little skate, Raja erinacea.

Renal micropuncture and microdissection techniques with ultramicro fluid analysis have been applied to evaluate single nephron function in the skate, Raja erinacea. We have divided the skate nephron into three proximal tubular segments (PTS I-III), three distal coilings (DC I-III), and a countercurrent loop system located between the proximal segments and the distal coilings. The collecting duct is the principal site of urinary dilution. Following exposure of the fish to 75% seawater for about 24 hours, the sodium concentration difference between the end collecting duct lumen and plasma is decreased sufficiently to account for the urinary dilution. The principal site for magnesium, phosphate and sulphate secretion appears to be PTS II. This segment is located on the ventral surface of the kidney. PTS II is also the main nephron site for reabsorption of sodium and chloride in excess of water.

Animals↗
PubMed1976

Elemental analysis of biological specimens in air with a proton microprobe.

The unique capabilities of the proton microprobe in an atmospheric environment as a biological tool are illustrated in studies of arsenic and mercury distributions in siingle strands of hair from poisoning victims and of the distributions of several abundant elements in frozen hydrated eye and kidney specimens from rats.

Animals↗
PubMed1975

Distal site of action of parathyroid hormone on phosphate reabsorption.

The sites of inhibited phosphate transport following administration of bovine parathyroid hormone (bPTH) to thyroparathyroidectomized (TPTX) dogs were investigated. Phosphate reabsorption by the proximal and distal nephron was studied using recollection micropuncture, stop-flow methodology, and electron-probe microanalysis. Following bPTH, delivery of phosphate from the proximal tubule increased from 26 to 37% of the filtered load, P less than .01. Fractional phosphate excretion increased from 2.3 +/- 1.5 to 21.4 +/- 2.3%, P less than .001. The increased delivery of phosphate at the point of micropuncture in the proximal tubule accounted for approximately half of the phosphaturia. In six TPTX dogs, which were saline loaded, similiar increases in phosphate delivery from the proximal tubule from 27 +/- 1 to 36 +/- 2% of the filtered load resulted in a strikingly smaller phosphaturia, 5.1 +/- 1 to 9.8 +/- 2.4%, NS. In stop-flow experiments, phosphate concentratin ratios were slightly increased in the proximal nephron and markedly increased in the distal nephron following bPTH. It is concluded that parathyroid hormone markedly decreases phosphate transport in the distal nephron.

Aminohippuric Acids↗