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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tubular transport of oxalate is thought to be an energy-mediated process which may contribute to the renal deposition of calcium oxalate in a variety of pathologic states. In order to examine this possibility, the renal handling of oxalate was investigated in rat renal cortical slices in vitro. Slices incubated in vitro with 1 microM [14C]oxalate in Krebs-Ringer bicarbonate buffer at 25 degrees C for 180 min achieved a mean slice to medium ratio of 2.8 +/- 0.08 (SEM) and a mean tissue concentration of 7.7 +/- 0.2 mumol/kg dry wt (N = 64). Section freeze-dry autoradiographs demonstrated maximum uptake within proximal tubule cells but no crystals were evident. Substituting N2 for O2, adding KCN, or removing Ca2+ increased uptake of 14C-oxalate. Dinitrophenol (DNP) and iodoacetamide (IoAc), however, significantly decreased, and O degrees C eliminated slice uptake. Slices incubated with 100 microM [14C]oxalate showed a further increase in tissue accumulation and the appearance of [14C]oxalate crystals. Crystals formed in vitro were deposited throughout the tissue. Oxalic acid did not appear to share the organic acid by renal cortical slices in vitro is largely independent of energy-mediated mechanisms.
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PMID:Oxalate accumulation in rat renal cortical slices. 647 47

The ultrastructure of the proximal tubule of mature mesonephric nephrons was studied in perfusion-fixed pig embryos of the 41st gestational day. Despite its 8-12 mm long course, the proximal tubule possesses no cytologically different subsegments except its very last cells at the abrupt transition into the distal tubule. The first brush-bordered proximal tubule cells stand considerably within Bowman's capsule, abuting its attenuated cells. In SEM specimens, the average luminal cell diameters are 8 X 13 micron. The cells are 6-11 micron in height with overlying microvilli 2-4 micron long. Lateral faces of perfectly disjoined cells exhibit plate-like interdigitating processes projecting more than 5 micron deep into the neighboring cells. The basal cell face is completely covered with microvilli. The TEM pictures reveal an endocytic apparatus largely matching its metanephric counterpart. Mitochondria account for 23% of the cytoplasm and together with the many basolateral cell membranes indicate a high capacity for energy-dependent transport processes. Small basal lipid droplets represent a species peculiarity. Freeze-fracture specimens show an electrocoupling of the cells by gap junctions. The tight junction, with only 1-2 strands, characterizes a "leaky" epithelium. In most features, this tissue is as mature as its metanephric counterpart.
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PMID:The pig mesonephros. II. The proximal tubule: SEM, TEM and freeze-fracture images. 666 May 64

The renal effects of sodium vanadate (Na3VO4), an inhibitor of sodium-potassium-ATPase recently shown to be a potent diuretic, were studied by using clearance and micropuncture techniques in nondiuretic anesthetized rats. Administration of 1.0 mumole of sodium vanadate (high dose) increased urine flow rate (V) from 9.8 +/- 1.4 to 17.5 +/- 4.0 microliter/min (mean +/- SEM, P < 0.025), UNaF from 1.73 +/- 0.36 to 3.05 +/- 0.65 microEq/min (P < 0.025), and FENa from 0.67 +/- 0.15 to 1.24 +/- 0.28% (P < 0.025)., No significant changes in GFR or RPF were observed. Late proximal tubular-fluid-to-plasma (F/P) inulin decreased from 2.28 +/- 0.19 to a minimum value of 1.38 +/- 0.06 (P < 0.025). Absolute water reabsorption decreased from 15.8 +/- 3.5 to 6.5 +/- 1.7 nl/min (P < 0.025) and fractional water reabsorption from 52.0 +/- 4.4 to 26.5 +/- 4.1% (P < 0.025). The injection of 0.5 mumole of sodium vanadate (low dose) resulted in no significant changes in V. Late proximal F/P inulin decreased, however, from 2.37 +/- 0.14 to a minimum value of 1.59 +/- 0.12 (P < 0.025). SNGFR remained unchanged, as did GFR and RPF. UNaV increased from 1.41 +/- 0.35 to 2.25 +/- 0.35 microEq/min (P < 0.025), and FENa rose from 0.64 +/- 0.16 to 0.91 +/- 0.15% (P < 0.025). The decrease in F/P inulin was observed in all but one animal, even in the absence of a diuretic response. The amount of fluid remaining in the lumen of the late proximal tubule was virtually the same in both low- and high-dose animals (18.9 +/- 3.0 and 19.5 +/- 3.4 nl/min, respectively). We conclude that sodium vanadate causes a decrease in superficial proximal tubule fluid and salt reabsorption. Inasmuch as the low dose does not result necessarily in a diuretic response, an increase in fluid reabsorption distal to the late proximal tubule must take place.
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PMID:Effects of sodium orthovanadate on whole kidney and single nephron function. 690 86

The fractional reabsorption (FR) of inorganic phosphate (Pi) along the proximal tubule depends upon both the filtered load of Pi (FLPi) and the tubular reabsorptive capacity of the Pi transporting system. To assess the actual effect of parathyroid hormone on the reabsorptive capacity only, the influence of Pi load has to be eliminated. In this study FRPi was determined by free-flow micropuncture along superficial nephrons of chronically (48 h) thyroparathyroidectomized (TPTX) and pair-fed sham-operated (SHAM) rats at identical FLPi [TPTX 3.07 +/- 0.14 (n = 26) and SHAM 3.07 +/- 0.11 (n = 26) mumol/min +/- SEM]. The micropuncture results indicate that in the ranges of tubular fluid over plasma inulin concentration [TF/P)In] 1.00-1.49 and 1.50-1.99, no difference in FRPi between TPTX and SHAM could be detected. It is only between a TF/PIn of 2.0 and 2.49 that chronic TPTX resulted in a significant increase in FRPi. Accordingly the present study indicates that chronic TPTX increases FRPi in late but not in early portions of proximal tubule. Thus in the early proximal tubule the tubular reabsorptive capacity of the Pi transporting system appears to be unaffected by chronic removal of the parathyroid glands. From this result it can be inferred that the increased plasma concentration of Pi which follows the removal of the parathyroid glands, particularly in the chronic stage, will lead to an apparently paradoxical decrease in FRPi in early proximal tubule as a mere consequence of the increased filtered load of Pi.
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PMID:Chronic thyroparathyroidectomy and tubular handling of phosphate: increased reabsorption in late but not in early proximal tubule. 719 57

Renal tubular reabsorption of L-histidine (His) was measured in vivo et situ by continuous microperfusion and free flow micropuncture of single proximal convoluted tubules of the rat kidney. The reabsorption is shown to be saturable. A permeability coefficient (P) of less than 29 microns 2 . s-1, a maximum reabsorption rate (J max) of 2.75 +/- 1.05 greater than J max greater than 1.97 +/- 0.86 (SEM) nmol . m-1 . s-1 and an affinity constant (Km) of 13.8 +/- 4.2 greater than Km greater than 10.9 +/- 4.0 (SEM) mol . 1-1 (lower values for P = 29 microns 2 . s-1, higher values for P = 0) were calculated from the microperfusion data. Using these constants and taking backflux of His and water reabsorption into account a good fit with the concentration profile of His along the proximal tubule--measured by free flow micropuncture--was obtained. Varying the buffered pH-values of the perfusion fluids (5.0 or 7.4) influenced neither the active reabsorption nor passive permeability of His. This indicates that the charge of the imidazol group of His does not play a significant role in His reabsorption. Further experiments showed that the addition of 20 mmol . 1-1 L-arginine--a strong inhibitor of the reabsorption system for dibasic amino acids--did not have a significant effect on the reabsorption of L-histidine. It is concluded, therefore, that His is reabsorbed by a system for neutral amino acids. Non ionic diffusion does not play an important role for His reabsorption.
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PMID:Renal handling of L-histidine studied by continuous microperfusion and free flow micropuncture in the rat. 719 54

Transmission electron micrographs of the mesonephric nephron in 18 day rabbit embryos reveal major cytological structures reappearing in the nephron of the definitive rabbit kidney. The initial segment of the proximal tubule resembles (despite quite different cell proportions) the cell picture of the metanephric S2-segment. The changes occurring at the end of the terminal proximal segment, the decrease in cell size, flattening of the nuclei, shortening of the brush border and reduction of Golgi profiles and endocytotic organelles largely parallel those between S2 and S3. The type of increased basolateral cell face of the proximal and distal tubule cells shows only quantitative differences to their metanephric counterparts. The distal tubule, which cannot be further subdivided (except the macula densa-region) exhibits varying degrees of cell interdigitations with vertically arranged and partially arching lateral ridges. This tubule matches closely the metanephric medullary straight part of the distal tubule, so that the sequence of the first mesonephric nephron segments is similar to the metanephric ones with the exception that the thin limb of Henle is absent. The large macula densa-region is characterized by its cell height and distended infranuclear spaces. The principal cells of the collecting tubule, with a few basal infoldings and intense short lateral interlockings resemble metanephric cells of the outer medullary collecting duct. The mitochondria-rich intercalated cells occur in dark and light contrasting forms and are more frequent than was evident from our SEM-study. The homogenous cell population of the Wolffian duct is characterized by large glycogen deposits and comparatively smooth cell faces.
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PMID:The mature mesonephric nephron of the rabbit embryo. II. TEM-studies. 724 60

Various enzymatic urinary activities have been proposed to assess renal proximal tubule damage in children, including neonates. Nevertheless comprehensive knowledge on the developmental aspects of physiological enzymuria is limited, particularly with regard to lysosomal and brush border enzymuria. Urinary activities of two lysosomal enzymes, N-acetyl-beta-D-glucosaminidase (NAG) and beta-galactosidase (GAL), and of two brush border enzymes, alanine aminopeptidase (AAG) and gamma-glutamyltransferase (GGT) were comparatively investigated in normal prematures (n = 28), term neonates (n = 52), infants aged less than 2 years (n = 19) and children (n = 33), and compared to urinary excretion of beta 2-microglobulin (B2M). Enzymatic activities were assayed using either spectrophotometrical (NAG, AAP, GGT) fluorimetrical (GAL) or radioimmunological (B2M) methods, and were related to urinary creatinine excretion. Developmental profiles of both the studied lysosomal enzymes and of B2M were similarly characterized with significantly decreasing values from prematures (NAG 9.29 +/- 1.44, GAL 2.26 +/- 0.26 IU/mmol creatinine, indicated as mean +/- SEM) to term neonates (6,94 +/- 0.58 and 1.76 +/- 0.15 IU/mmol creatinine, respectively) and older infants and children. Lysosomal enzymatic urinary activities correlated linearly with a coefficient of r = 0.75, (p < 0.05), while correlations between each lysosomal enzymatic activity and B2M urinary excretion were weaker.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Specific developmental profiles of lysosomal and brush border enzymuria in the human. 772 20

To see if arginine vasopressin (AVP) influenced fetal sodium balance, we infused AVP i.v. (45 mU h-1 kg-1) into two groups of chronically catheterized fetal sheep. One group had urinary osmolalities of 147 +/- 23 mosm kg-1 (SEM, n = 6) and the other group had higher urinary osmolalities (339 +/- 3 mosm kg-1, n = 4, P < 0.001). The group with high urinary osmolalities had higher systolic pressures (P < 0.05), higher glomerular filtration rates (GFR; P < 0.05), and higher urinary electrolyte excretion rates (P < 0.05), but lower membrane blood flows (P < 0.05) and lower fractional reabsorption of sodium by the proximal tubule (P < 0.01). In the group with low urinary osmolalities, AVP caused a rise in arterial blood pressure (P < 0.001), a fall in heart rate (P < 0.001), a fall in membrane blood flow (P < 0.02), but no change in placental or renal blood flow. Renal sodium excretion increased (P < 0.001) because GFR rose (P < 0.001) and proximal fractional sodium reabsorption fell (P < 0.001). Distal fractional sodium reabsorption increased (P < 0.001), but not enough to compensate for the fall in proximal fractional reabsorption. Lung liquid flow decreased (P = 0.006), as did lung liquid sodium excretion (P = 0.002). There were no changes in fetal plasma sodium, blood volume or haematocrit. The effects of AVP infusion were similar in the group with high urinary osmolalities. This study shows that high levels of AVP, such as occur in fetal "stress", have widespread effects on fetal cardiovascular, renal and lung functions. The characteristic profile of the fetuses with high urinary osmolalities prior to AVP infusion could be entirely explained by high endogenous AVP levels and AVP could possibly be a sole mediator of these widespread effects of fetal "stress". Furthermore, although during infusion of AVP sodium excretion increased, blood volumes did not change. Therefore, the fetuses must have accessed additional sodium from either their extracellular fluids, the amniotic and/or allantoic cavities or across the placenta.
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PMID:The roles of arginine vasopressin in fetal sodium balance and as a mediator of the effects of fetal "stress". 808 38

One possible factor for glomerular hyperfiltration in early diabetes could be a deficiency of renal vasoconstrictive mechanisms. Dipyridamole (DIP) inhibits cellular uptake of adenosine thereby increasing interstitial adenosine concentration. The effect of DIP on tubuloglomerular feedback (TGF) and on urinary protein excretion (UPE), glomerular filtration rate (GFR), and kidney weight was studied in early diabetes in rats. One day after onset of streptozotocin (STZ)-induced insulin-dependent diabetes mellitus (IDDM) daily treatment with DIP (50 mg/100 g twice a day via a gastric tube) was started in one group (STZ-DIP) and with vehicle alone in another group (STZ). Rats were housed in metabolic cages for 24 h to measure UPE 7, 14, and 21 days after STZ-injection. Non-diabetic animals, also receiving vehicle, served as controls (CON). While 7, 14, and 21 days after STZ-injection UPE was enhanced by 88, 123, and 153% in the STZ-group (n = 5) as compared to the CON-group (n = 6), the increase in UPE in the STZ-DIP-group (n = 5) was reduced by 82, 66, and 60%, respectively. Subsequently these diabetic rats were prepared for clearance and micropuncture study. Weight-matched (wm) non-diabetic rats served as controls (CONwm). TGF activity was assessed as the difference between stop flow pressures (delta SFP) in the early proximal tubule at 0 and 50 nl/min perfusion rates of Henle's loop. delta SFP was 8.8 +/- 0.7 mmHg (mean +/- SEM) in the CONwm-group (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Dipyridamole prevents diabetes-induced alterations of kidney function in rats. 817 May 6

The ability of renal cells to regenerate is critical for the recovery of renal function following injury. Research on the recovery of renal function has been limited by the lack of in vitro models of renal repair. The goal of this study was to develop an in vitro model of renal proximal tubule cell (RPTC) injury and regeneration using primary cultures of rabbit RPTC. Renal proximal tubules were isolated and cultured in hormonally defined DME/F-12 medium at 37 degrees C under 95% air/5% CO2. RPTC were grown to confluency, made quiescent by the removal of insulin and hydrocortisone from the medium for 24-48 hr, and treated with the nephrotoxicant, 1,2-dichlorovinyl-L-cysteine (DCVC). DCVC (100 microM for 2 hr, n = 3-6) resulted in cell injury and the release of nonviable cells from the plate at 24 hr (55% +/- 6% confluency, mean +/- SEM) and 48 hr (37% +/- 7% confluency). Cell monolayers began to regenerate 96 hr after exposure (57% +/- 9% confluency) and continued to regenerate reaching 76% +/- 8% and 84% +/- 1% confluency by 6 and 8 days postexposure. Control cells maintained confluency throughout the experiment. Thus, an in vitro primary cell culture model has been developed in which the cell monolayer regenerates after nephrotoxicant-induced injury. This model may be useful in the study of mechanisms of renal cell injury and repair.
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PMID:An in vitro model of renal proximal tubule cell regeneration. 840 Apr 16


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