bluuebunny/crossref_metadata_2025 huggingface dataset:
TGF-beta stimulates rat mesangial cell proliferation in culture: role of PDGF beta-receptor expression
Authors: Haberstroh U. , Zahner G. , Disser M. , Thaiss F. , Wolf G. , Stahl R. A.
Published: December 2017

Transforming growth factor (TGF)-beta is known to increase mesangial cell (MC) matrix; however, its possible role on MC proliferation is controversial. We therefore studied the influence of TGF-beta on MC proliferation in culture and evaluated its effect on the platelet-derived growth factor (PDGF) B-chain as well as the expression of the PDGF beta-receptor. TGF-beta (1 ng/ml) increases MC DNA synthesis by approximately threefold after 48 h of incubation. TGF-beta-induced MC proliferation was also confirmed by cell counts. A neutralizing anti-TGF-beta antibody completely blocked this growth promoting activity. The levels of PDGF beta-receptor steady-state mRNA were increased by TGF-beta at 48 h. This was associated with an increase in receptor density per cell as measured by receptor kinetic studies. PDGF B-chain mRNA was also increased by TGF-beta at 48 h. A neutralizing anti-PDGF B-antibody causes no reduction of TGF-beta-induced DNA synthesis; however, suramin completely inhibited the mitogenic effect of TGF-beta. We conclude that TGF-beta stimulates MC growth in long-term culture, a process in which upregulation of the PDGF beta-receptor and enhanced synthesis of PDGF B-chain might be involved.
Hypertonic sucrose treatment enhances second messenger accumulation in vasopressin-sensitive cells
Authors: Lutz W. , Kumar R.
Published: December 2017

When we treated vasopressin-sensitive vascular smooth muscle cells (A10 cells) and kidney cells (LLC-PK1 cells) with hypertonic sucrose and vasopressin, we observed a decrease in the internalization of radiolabeled vasopressin into these cells and an increase in the amount of second messenger present in these cells following vasopressin stimulation. In A10 cells exposed to hypertonic sucrose, there was an increase in the amount of cellular inositol phosphates accumulated in response to vasopressin compared with cells not exposed to hypertonic sucrose. Similarly, in hypertonic sucrose-treated LLC-PK1 cells, vasopressin increased the amount of adenosine 3',5'-cyclic monophosphate (cAMP) present within the cells compared with LLC-PK1 cells not exposed to hypertonic sucrose. Hypertonic sucrose treatment inhibited receptor-mediated endocytosis in both these cell lines. Hypertonic sucrose alone did not increase the basal amounts of inositol phosphates or cAMP present in A10 or LLC-PK1 cells, respectively. Hypertonic sucrose treatment inhibits receptor endocytosis and increases second messenger concentrations in vasopressin-sensitive cells.
Nephron specificity of dopamine receptor-adenylyl cyclase defect in spontaneous hypertension
Authors: Ohbu K. , Felder R. A.
Published: December 2017

Since DA1 receptors regulate renal tubular sodium transport, it is possible that the reported defect in the coupling between the DA1 dopamine receptor and adenylyl cyclase (AC) in the proximal tubule (PT) is a mechanism for the increased sodium reabsorption in animal models of spontaneous hypertension. Because the distal nephron may participate in the increased sodium retention in the spontaneously hypertensive rat (SHR), we determined whether the defective DA1 receptor-AC coupling described in PT of SHR is also present in the cortical collecting duct (CCD). Radioligand binding studies with the DA1 antagonist 125I-Sch 23982 revealed similar dissociation constants and maximum receptor densities in the CCD from Wistar-Kyoto rats (WKY) and SHR. Fenoldopam, a DA1-selective agonist, stimulated AC activity to a similar extent in CCD from both rat groups. Therefore the defective DA1 receptor-AC coupling in SHR has nephron segment specificity, since it is present in PT but not in CCD. One of the AC-linked dopamine receptors is an intronless D1A cloned from brain, which is also present in PT. Because the coupling defect in the PT may reside in the third cytoplasmic loop (involved in G protein coupling), we compared the sequence of this segment of the cloned D1A receptor using genomic DNA. Because no differences were noted between WKY and SHR, the coupling defect in the PT is not due to a mutation at the third cytoplasmic loop of the D1A receptor.
Ammonium and bicarbonate transport in isolated perfused rodent long-loop thin descending limbs
Authors: Flessner M. F. , Mejia R. , Knepper M. A.
Published: December 2017

Ammonium accumulates in the renal medullas of antidiuretic mammals. The accumulation process is thought to involve countercurrent multiplication, energy-dependent recycling between the ascending and descending limbs of Henle's loop. To investigate the role of the long-loop thin descending limb (LDL) in countercurrent multiplication of ammonium, we have perfused outer medullary and inner medullary subsegments of the chinchilla LDL (and inner medullary subsegments of rat LDL) in vitro and measured the fluxes of total ammonia and total CO2. No spontaneous fluxes of total ammonia or total CO2 occurred in the absence of imposed concentration gradients. When transepithelial concentration gradients were imposed, passive total ammonia and total CO2 transport were observed in all subsegments, although the permeabilities varied with distance along the descending limb. Passive total ammonia transport occurred through a combination of NH3 and direct NH4+ permeation. The outer medullary segment was the most permeable to NH4+. The deep inner medullary segment was the most permeable to bicarbonate. Addition of carbonic anhydrase to the lumen accelerated passive NH3 entry in the outer medullary LDL, indicating that little or no luminal carbonic anhydrase is endogenously present. The passive secretion of NH4+ and NH3 into the LDL may contribute to the countercurrent multiplication of ammonium in the rodent renal medulla.
Calcitriol stimulates Na(+)-Pi cotransport in a subclone of opossum kidney cells (OK-7A) by a genomic mechanism
Authors: Allon M. , Parris M.
Published: December 2017

Calcitriol (CT) stimulates Na(+)-Pi cotransport in a subclone of opossum kidney cells (OK-7A) by a genomic mechanism. An experimental model of renal proximal tubular cells in which CT affects Na(+)-Pi cotransport would be useful for examining the mechanisms of this effect. This study evaluated the effect of CT on Na(+)-Pi cotransport in opossum kidney (OK) cells. CT had no effect on Na(+)-Pi cotransport in wild-type OK cells and in the OK-B, OK-H, and OK-P subclones. In contrast, CT at physiological concentrations stimulated Na(+)-Pi cotransport in the OK-7A subclone; the effect was dose related with a 52% increase at 10(-11) M CT, as well as a maximal twofold stimulation at 10(-9) M. CT (10(-11) M) increased the maximum uptake for Na(+)-Pi cotransport (Vmax = 3.55 +/- 0.16 vs. 2.51 +/- 0.17 nmol.mg protein-1.5 min-1, P < 0.01), without affecting the apparent Michaelis constant (Km = 30.6 +/- 1.0 vs. 30.8 +/- 0.7 microM). The stimulatory effect on Na(+)-Pi cotransport was specific for CT and did not occur with 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3, or 1 beta,25-dihydroxyvitamin D3. At 10(-11) M CT, the stimulation of Na(+)-Pi uptake in OK-7A cells was maximal at 3 h; it was completely abolished by preincubation with actinomycin D or cycloheximide. Both calphostin C, an inhibitor of protein kinase C (PKC), or prolonged incubation with phorbol 12-myristate 13-acetate, to downregulate the PKC pathway, partially inhibited the stimulatory effect of CT on Na(+)-Pi cotransport in OK-7A cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Selective transcriptional augmentation of hepatic gene expression in the rat with Heymann nephritis
Authors: Sun X. , Martin V. , Weiss R. H. , Kaysen G. A.
Published: December 2017

The synthesis of albumin and other hepatic proteins, many regulated as part of the acute phase response, is increased in the nephrotic syndrome. It has been postulated that synthesis of all proteins secreted by the liver is increased by the same mechanism in the nephrotic syndrome. However, the observation that synthesis of some apolipoproteins is not increased suggests that only a specific group of proteins may be similarly regulated in nephrosis. We measured synthesis of albumin and of two acute phase proteins, fibrinogen and alpha 1-acid glycoprotein (alpha 1-AG), in rats with Heymann nephritis (HN), their mRNA concentration in liver, and the rate of transcription of their genes by hepatic nuclei. Albumin and fibrinogen mRNA levels almost doubled in HN, but alpha 1-AG mRNA was unchanged. Ribosomal RNA (28S) concentration and transcription were also increased significantly in HN. Transcription of albumin and fibrinogen also increased twofold, but transcription of alpha 1-AG was unchanged. Fibrinogen and albumin synthesis each increased more than fourfold in HN and correlated with one another. In contrast alpha 1-AG synthesis only increased by 50% and did not correlate with albumin synthesis. Both albumin and alpha 1-AG were lost in the urine of HN, and their plasma concentrations were reduced. Fibrinogen was not lost in the urine and its plasma concentration was significantly increased in HN. Synthesis of a group of proteins including both positive acute phase (fibrinogen) and negative acute phase (albumin) proteins is increased transcriptionally in the nephrotic syndrome. Synthesis of other proteins is increased posttranscriptionally.(ABSTRACT TRUNCATED AT 250 WORDS)
Urea selectively induces DNA synthesis in renal epithelial cells
Authors: Cohen D. M. , Gullans S. R.
Published: December 2017

Hyperosmotic stress with the functionally impermeant solute NaCl has been shown by us and others to inhibit cell growth and DNA synthesis. Several lines of evidence suggest that urea, the other principal renal medullary solute, may exert a growth-promoting effect on renal epithelial cells. Among these is the finding that urea upregulates expression at the mRNA level of two growth-associated immediate-early genes, Egr-1 and c-fos. In the present study, urea, in concentrations characteristic of the renal medulla, increased [3H]thymidine incorporation approximately threefold in confluent, growth-suppressed Madin-Darby canine kidney (MDCK) cells, whereas another readily membrane-permeant solute, glycerol, did not. Urea also overcame the inhibitory effect of hyperosmotic NaCl on DNA synthesis. The urea-induced increase in [3H]thymidine incorporation was also evident in the renal epithelial LLC-PK1 cell line, but not in renal nonepithelial and epithelial nonrenal cell types examined. In addition, it was associated with a 15% increase in total DNA content measured fluorometrically at 24 h of treatment. There was, however, no associated increase in cell proliferation as measured by cell number, total protein content, or cell cycle distribution. Urea also failed to induce polyploidy or aneuploidy. Therefore cells of renal epithelial origin may be uniquely capable of responding to hyperosmotic urea with increased DNA synthesis through an undefined and potentially novel mechanism.
Autocrine/paracrine regulation of renal Na(+)-phosphate cotransport by dopamine
Authors: Glahn R. P. , Onsgard M. J. , Tyce G. M. , Chinnow S. L. , Knox F. G. , Dousa T. P.
Published: December 2017

We tested the hypothesis that dopamine (DA) acts as an autocrine/paracrine regulator of Na(+)-Pi symport in proximal tubules, using opossum kidney (OK) cells as an in vivo model. Both DA and parathyroid hormone (PTH) increased adenosine 3',5'-cyclic monophosphate (cAMP) and inhibited Na(+)-gradient-dependent uptake of 32P but not that of L-[3H]-alanine. Incubation of OK cells with L-dopa, a DA precursor, resulted in accumulation of DA (7.4 nM), a ninefold increase of cAMP in the medium, and an inhibition (-10%) of Na(+)-Pi uptake. Carbidopa, an inhibitor of aromatic-L-amino acid decarboxylase, prevented the formation of DA from L-dopa, the increase in cAMP, and the inhibition of Na(+)-Pi cotransport. Pi-replete OK cells produced more DA (+15%) from L-dopa than Pi-deprived cells; however, the endogenous DA inhibited Na(+)-Pi cotransport both in Pi-deprived and in Pi-replete cells. Thus OK cells can synthesize DA from L-dopa in a quantity sufficient to elicit both the maximum DA-stimulated cAMP accumulation and inhibition of Na(+)-Pi cotransport in the same cell population. Our data, obtained on an in vitro system, support the hypothesis proposing that DA generated in proximal tubular cells can modulate, via cAMP, the Na(+)-Pi symport in the same or adjacent cells. If present in the kidney, this pathway might represent an autocrine/paracrine system that can contribute to regulation of renal Pi homeostasis.
Sex differences in control of renal outer medullary circulation in rats: role of prostaglandins
Authors: Parekh N. , Zou A. P. , Jungling I. , Endlich K. , Sadowski J. , Steinhausen M.
Published: December 2017

A calibration technique was developed to quantify blood flow changes in the renal cortex and outer medulla in rats using platinum needle electrodes sensing partial pressure of locally generated hydrogen. Measurements were made in male and female rats to investigate sex differences in the humoral control and autoregulation of regional renal circulations. In males, both cortical and outer medullary blood flows were efficiently auto-regulated above an arterial pressure of 100 mmHg. The converting-enzyme inhibitor quinapril increased blood flow by 20% in both kidney zones, and inhibition of prostaglandin synthesis by indomethacin did not change the flow. In females, similar results were obtained only for the cortex; the medulla had a different response pattern. The blood flow was not autoregulated in the experimental pressure range up to 120 mmHg; quinapril did not change the flow, but indomethacin decreased the flow by 16% and at the same time restored its autoregulation capacity. We conclude that: 1) the medulla of female rats has a high basal level of vasodilator prostaglandins, which interferes with blood flow autoregulation in this kidney area, and 2) medullary flow in female rats is little affected by endogenous angiotensin.
Maintenance of endothelin-induced renal arteriolar constriction in rats is cyclooxygenase dependent
Authors: Munger K. A. , Takahashi K. , Awazu M. , Frazer M. , Falk S. A. , Conger J. D. , Badr K. F.
Published: December 2017

Influence of arachidonate cyclooxygenase (COX) products on endothelin (ET)-evoked renal vasoconstriction was assessed. In microperfused rat afferent (AA) and efferent arterioles (EA), indomethacin had no effects on the maximal contraction of both AA and EA by ET, but reduced the duration of ET-induced constriction in both arterioles. ET infusion to rats in vivo resulted in a selective increase in efferent but not afferent arteriolar resistance, leading to a dramatic increase in transcapillary hydraulic pressure difference. Glomerular filtration rate (GFR), which fell progressively during infusion of ET alone, was markedly preserved by COX inhibition, but not during selective thromboxane A2 antagonism. In isolated glomeruli, release of prostaglandin (PG) F2 alpha in response to 10(-6) mol/l ET exceeded that the PGE2 by a ratio of 3.2. Collectively, these data provide strong evidence that locally released COX products, possibly PGF2 alpha, play a key role in sustaining ET-induced renal arteriolar constriction. COX inhibition leads to acute vasorelaxation of AA despite continued ET administration, without affecting EA constriction in vivo, thereby resulting in a dramatic reversal of the effects of ET on GFR.
Natriuretic peptides inhibit mesangial cell production of endothelin induced by arginine vasopressin
Authors: Kohno M. , Horio T. , Ikeda M. , Yokokawa K. , Fukui T. , Yasunari K. , Murakawa K. , Kurihara N. , Takeda T.
Published: December 2017

The present study examined the effects of atrial, brain, and C-type natriuretic peptides (ANP, BNP, and CNP, respectively) on endothelin-1 (ET-1) secretion after stimulation with arginine vasopressin (AVP), using cultured rat glomerular mesangial cells. AVP stimulated immunoreactive (ir) ET-1 secretion in a concentration-dependent manner via a receptor-mediated process. Rat ANP-(1-28) and rat BNP-45 potently inhibited this stimulated secretion in a concentration-dependent manner. Inhibition by ANP and BNP of AVP-stimulated ET-1 secretion was paralleled by an increase in the medium level of guanosine 3',5'-cyclic monophosphate (cGMP). The addition of a cGMP analogue, 8-bromo-cGMP, reduced the stimulated ET-1 secretion. CNP was much less effective than rat ANP-(1-28) or rat BNP-45 with respect to inhibiting irET-1 secretion and increasing cGMP levels. High-performance liquid chromatography indicated that the major component of irET-1 in the culture medium corresponds to ET-1-(1-21). These findings indicate that AVP stimulates ET-1 secretion in cultured rat mesangial cells and that rat ANP and BNP inhibit this stimulated secretion, probably through a cGMP-dependent process.
Effect of hyperosmolality on production and mRNA expression of ET-1 in inner medullary collecting duct
Authors: Yang T. , Terada Y. , Nonoguchi H. , Ujiie K. , Tomita K. , Marumo F.
Published: December 2017

The effects of hyperosmolality on the production and mRNA expression of endothelin-1 (ET-1) in inner medullary collecting duct (IMCD) were examined in the present study. Osmolality in incubation media was changed from 290 to 490 or 690 mosmol/kgH2O by adding NaCl, urea, mannitol, or raffinose. A preliminary experiment was carried out using tubule suspension from the inner medulla. Hyperosmolality by NaCl stimulated ET-1 accumulation in rats (from 323.5 +/- 76.3 to 478.0 +/- 108.4 and 573.7 +/- 47.8 pg.mg protein-1 x 24 h-1 in 290, 490, and 690 mosmol/kgH2O, respectively) and rabbits. In contrast, hyperosmolality by urea markedly decreased ET-1 accumulation and hyperosmolality by mannitol showed no effect on it. We next examined whether hyperosmolality changes ET-1 mRNA. After incubation in isotonic or hypertonic solution for 6 h, ET-1 mRNA was determined using reverse transcription and polymerase chain reaction (PCR) in microdissected IMCD and glomerulus. Hyperosmolality by NaCl and raffinose significantly increased the PCR products of ET-1 mRNA in IMCD, whereas mannitol did not. The stimulatory effect of hyperosmolality by NaCl on ET-1 mRNA expression was not observed in glomerulus. Our data suggested a stimulatory effect of hyperosmolality on production and mRNA expression of ET-1 in IMCD but not in glomerulus.
Osmotic adaptation of renal medullary cells during transition from chronic diuresis to antidiuresis
Authors: Sone M. , Albrecht G. J. , Dorge A. , Thurau K. , Beck F. X.
Published: December 2017

The cells of the renal medulla adapt osmotically to high extracellular tonicities by high concentrations of organic osmolytes. Intracellular accumulation of these substances is, however, relatively slow. The aim of the present study was to assess the effect of an abrupt rise in extracellular tonicity on intracellular osmotically active substances after prior reduction of medullary contents of organic osmolytes by chronic diuresis. Intra- and extracellular electrolyte concentrations at the papillary tip and the tissue contents of methylamines (glycerophosphorylcholine, betaine), polyols (myo-inositol, sorbitol), and several amino acids were determined in the different kidney zones by electron microprobe analysis and high-performance liquid chromatography in control animals, in rats infused for 6 days with furosemide via osmotic minipumps, and in rats given the vasopressin analogue [deamino-Cys1,D-Arg8]vasopressin (DDAVP) after the chronic furosemide treatment. Chronic diuresis greatly reduced interstitial tonicity and inner medullary contents of methylamines and polyols and moderately reduced inner medullary amino acid contents but did not significantly affect intracellular electrolyte concentrations. When the diuretic rats were infused with DDAVP for 2 h, interstitial tonicity more than doubled and intracellular K and Cl concentrations rose by approximately 60 and 160%, while inner medullary contents of methylamines, polyols, and amino acids were not changed significantly. These data demonstrate that after effective depletion of medullary organic osmolytes by long-term diuresis, the cells of the renal papilla adapt osmotically to an abrupt increase in extracellular tonicities by elevated cell electrolyte concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of phosphorus restriction on renal response to oral and intravenous protein loads in rats
Authors: Kraus E. S. , Cheng L. , Sikorski I. , Spector D. A.
Published: December 2017

Dietary phosphorus restriction ameliorates renal injury in rats. This may be due to changes in renal hemodynamics, including those factors associated with protein-induced hyperfiltration. To test this, we measured inulin clearance (CIn), p-aminohippuric acid clearance (CPAH), mean arterial blood pressure, and renal vascular resistance (RVR) 1 h before and 100 min after either oral gavage of 2 g bovine serum albumin or intravenous infusion of 5% glycine in female Sprague-Dawley rats previously fed for 3-8 wk a 0.5% or a 0.1% phosphorus diet. Baseline CIn, CPAH, blood pressure, and RVR were similar. After albumin gavage, CIn rose 20% (P < 0.01) for the 0.5% phosphorus group but did not change for rats fed the 0.1% phosphorus diet. Other measured parameters, including plasma glucagon and renin activity, were not influenced by dietary phosphorus content. In contrast, during intravenous infusion of glycine, hyperfiltration was induced in phosphorus-restricted rats. Thus dietary phosphorus restriction ablates oral protein but not intravenous amino acid-induced hyperfiltration, suggesting a gut-mediated mechanism for the former. These data highlight the potential importance of dietary phosphorus as a mediator of renal hemodynamics.
Organic osmolytes in acute hyponatremia
Authors: Sterns R. H. , Baer J. , Ebersol S. , Thomas D. , Lohr J. W. , Kamm D. E.
Published: December 2017

The defense of brain volume during hyponatremia cannot be explained by the losses of brain sodium and potassium. We have examined the brain losses of organic osmolytes in rats after 24 h of severe hyponatremia induced by the administration of vasopressin and 5% dextrose in water. Normonatremic controls and animals with intermediate plasma sodium concentration ([Na]) were produced in vasopressin-treated animals by the administration of isocaloric gavages containing varying amounts of NaCl and free water. The animals were killed at 24 h by decapitation, and one brain hemisphere was quickly frozen in liquid nitrogen for organic osmolyte determinations. When compared with controls (plasma [Na] = 139 +/- 1.5 mM), hyponatremic animals (plasma [Na] = 96 +/- 1 mM) had significantly reduced brain contents for sodium, potassium, chloride, glutamate, myo-inositol, N-acetylaspartate, aspartate, creatine, taurine, gamma-aminobutyric acid, and phosphoethanolamine. Plasma [Na] was highly correlated (P < 0.001) with the brain contents for sodium, potassium, and organic osmolytes. Whereas the observed increase in brain water during hyponatremia was only 4.8%, by calculation, brain swelling without brain organic osmolyte losses would have been 11%, an amount that jeopardizes survival.
Endothelin activation of phospholipase D: dual modulation by protein kinase C and Ca2+
Authors: Friedlaender M. M. , Jain D. , Ahmed Z. , Hart D. , Barnett R. L. , Nord E. P.
Published: December 2017

Previous work from this laboratory has identified an endothelin (ET) type A (ETA) receptor on cultured rat renal medullary interstitial cells (RMIC), coupled to phosphatidylinositol-specific phospholipase C (PI-PLC), dihydropyridine-insensitive receptor-operated Ca2+ channels, and phospholipase A2. The current studies explored a role for ET stimulation of phosphatidylcholine-specific phospholipase D (PC-PLD) in intracellular signaling of this cell type. ET stimulated PLD activation, as measured by phosphatidic acid (PA) or phosphatidylethanol (PEt) accumulation, in a time- and concentration-dependent manner. Inhibition of diacylglycerol (DAG) kinase by ethylene glycol dioctanoate or 6-(2)4-[(4-fluorophenyl)-phenylmethylene]-1-piperadinyl]ethy l-7-methyl-5H - thiaxolo-[3,2-alpyrimidin]-5-one (R 59022) failed to blunt PA accumulation, indicating that PLD, and not DAG, was the source of PA. Inhibition of PA phosphohydrolase (PAP) by propranolol increased late accumulation of PA, suggesting that the prevailing metabolic flow was in the direction of PA to DAG. Phorbol 12-myristate 13-acetate (PMA) augmented ET-evoked PEt accumulation, whereas downregulation of protein kinase C (PKC) obviated agonist-induced PEt production. PMA augmentation of PLD activity proceeded independent of cytosolic free Ca2+ concentration. Ca2+ derived from either intracellular or extracellular sources enhanced ET-related PEt accumulation but was without effect in PKC-downregulated cells. Collectively, these observations indicate that ET stimulates PLD production in RMIC. PKC is the major regulator of this process, with Ca2+ playing a secondary, modulatory role. In addition, these data suggest that PC-PLD is coupled to the ETA receptor.
Activity of 11 beta-hydroxysteroid dehydrogenase in toad bladder: effects of 11-dehydrocorticosterone
Authors: Brem A. S. , Matheson K. L. , Latif S. , Morris D. J.
Published: December 2017

11 beta-Hydroxysteroid dehydrogenase (11 beta-OHSD) transforms circulating glucocorticoids to their "biologically inert" 11-dehydro derivatives. Isoforms of 11 beta-OHSD with different cofactor requirements and biochemical properties [Michaelis constant (Km) and maximal velocity (Vmax)] exist in the kidney. Since epithelial cells derived from the toad bladder also contain this enzyme, we wished to further characterize its properties in prepared cell homogenates. 11 beta-OHSD from toad bladder demonstrated a clear preference for NAD+ over NADP+ as a cofactor similar to that observed in renal cortical collecting duct (CCD) cells. Furthermore, 11 beta-OHSD had a rapid onset of action. The apparent Km for corticosterone was 16.3 x 10(-8) M, a value comparable to that observed for enzyme from CCD, and a Vmax of 4.8 x 10(-12) mol.mg protein-1.min-1. The end product, 11-dehydrocorticosterone (compound A), influenced enzyme activity; it increased 11 beta-OHSD activity at corticosterone concentrations below the apparent Km for the enzyme and inhibited 11 beta-OHSD activity at corticosterone concentrations above the Km for the enzyme. The inhibitory effects of compound A appeared noncompetitive with an apparent equilibrium constant (Ki) of 2.8 x 10(-7) M. Consistent with its inhibitory action on 11 beta-OHSD, compound A (10(-6) M) enhanced the short-circuit current response to corticosterone (10(-7) M) in the intact toad bladder (experimental 2.03 +/- 0.33 vs. control 1.40 +/- 0.17 times above baseline; n = 7, P < 0.01). Thus 11 beta-OHSD in toad bladder resembles the isoform found in CCD, and compound A may be biologically important as a regulator of 11 beta-OHSD.
Aluminum inhibits bone nodule formation and calcification in vitro
Authors: Sprague S. M. , Krieger N. S. , Bushinsky D. A.
Published: December 2017

Cells isolated from neonatal mouse calvariae can be induced to form mineralized nodules after exposure to ascorbic acid and beta-glycerophosphate. To determine whether aluminum inhibits nodule formation and subsequent mineralization, cells isolated from neonatal mouse calvariae were induced to form nodules and incubated with increasing concentrations of aluminum (10(-7) to 10(-5) M). Compared with control and 10(-7) M aluminum-supplemented cultures, the number of nodules formed and the number of nodules calcified were reduced in cells incubated with 10(-6) and 10(-5) M aluminum. The cumulative net calcium uptake into the nodules and their final calcium content were also decreased with 10(-6) and 10(-5) M aluminum. After 10 and 18 days of incubation, aluminum did not affect DNA synthesis or release of alkaline phosphatase but significantly inhibited collagen production. Thus aluminum induced a dose-dependent inhibition of nodule formation and calcification that may be related to its inhibition of collagen production.
Effects of IGF-I on renal function in patients with chronic renal failure
Authors: O'Shea M. H. , Miller S. B. , Hammerman M. R.
Published: December 2017

Insulin-like growth factor I (IGF-I) has been shown to increase glomerular filtration rate and renal plasma flow in rats and humans with normal renal function. However, rats with reduced renal function are resistant to these effects. To determine whether IGF-I affects glomerular filtration rate and renal plasma flow in humans with reduced renal function, we administered recombinant human IGF-I (rhIGF-I) to patients with moderate chronic renal failure. Four patients whose baseline inulin clearances were 21.9, 23.2, 34.9, and 55.1 ml.min-1.1.73 m-2 were placed on a 1 g.kg-1.day-1 protein diet and studied over a 10-day period (0-10). On days 4-7, 100 micrograms/kg of rhIGF-I was subcutaneously administered twice daily to the patients. The effects of rhIGF-I on levels of circulating IGF-I, inulin clearance, p-aminohippurate (PAH) clearance, kidney volume, plasma glucose, plasma and urine calcium and phosphate, and urine sodium and protein were determined. Administration of rhIGF-I increased levels of circulating IGF-I, inulin clearances, PAH clearances, and kidney size in each of the four patients receiving the growth factor. IGF-I did not cause weight gain, natriuresis, proteinuria, or hypoglycemia. Plasma calcium and phosphate were not affected by rhIGF-I. However, the percent tubular reabsorption of filtered phosphate was increased. We conclude that administration of rhIGF-I can enhance glomerular filtration rate and renal plasma flow at least in some humans with moderately reduced renal function. The enhancement is associated with an increase in kidney volume.
Glomerular size selectivity during protein overload in the rat
Authors: Lemley K. V.
Published: December 2017

Differential glomerular permeability to macromolecules as a function of their size (size permselectivity) is altered in experimental models of proteinuric renal disease. Size permselectivity during protein overload proteinuria was examined using urinary clearances of neutral dextrans in anesthetized Wistar-Furth rats. The animals were studied 3-4 h after the last of six twice-a-day intraperitoneal injections of either bovine serum albumin (BSA) or ovalbumin (OA) or of vehicle alone (controls). Glomerular filtration rates did not differ significantly among the three groups. OA-treated (n = 4) and control (n = 5) rats had virtually identical fractional dextran clearances over almost the entire molecular size range from 18 to 58 A Stokes-Einstein radius. In contrast, BSA-treated rats (n = 5) had elevated fractional clearances for medium-sized dextrans with the increases reaching statistical significance at radii of 40 A (+22.7% vs. control) and 44 A (+20.4%). Fractional clearances for BSA-treated rats returned to control values for larger dextrans. These findings demonstrate a significant size permselectivity defect in BSA overload, although not in OA overload.
Relationships among protein and albumin concentrations and oncotic pressure in nephrotic plasma
Authors: Canaan-Kuhl S. , Venkatraman E. S. , Ernst S. I. , Olshen R. A. , Myers B. D.
Published: December 2017

We determined oncotic pressure (pi) by membrane osmometry and assayed total protein (TP) and albumin (Alb) concentrations in plasma of 102 nephrotic subjects and 27 healthy controls. All three quantities were markedly depressed in the nephrotic group. When plasma was serially diluted and concentrated, nephrotic but not control plasma also exhibited a highly variable change point in the nonlinear relationship between TP or Alb and pi. Absent a unique change point, we developed quadratic models which incorporated TP, Alb, and (TP x Alb) to prospectively predict pi in unperturbed plasma. The ability of the most successful quadratic model to predict pi in afferent or efferent arteriolar plasma was limited; the prediction errors reached 10 mmHg in nephrotic and 6 mmHg in control subjects. The nephrotic model coefficients also differed significantly from control and pointed to an important influence of nonalbumin proteins on pi in nephrotic plasma. Investigation of the intrinsic membrane properties of diseased glomerular capillary walls requires precise knowledge of pi. For this purpose we recommend that pi be directly determined by membrane osmometry rather than calculated from protein concentration(s).
Homeostatic efficiency of tubuloglomerular feedback in hydropenia, euvolemia, and acute volume expansion
Authors: Thomson S. C. , Blantz R. C.
Published: December 2017

We assessed the homeostatic efficiency of the tubuloglomerular feedback (TGF) system in Inactin-anesthetized Munich-Wistar rats by use of perturbation analysis in closed-loop micropuncture studies. Nephrons were studied in vivo under conditions of hydropenia (HYD, n = 17), euvolemia (EUV, n = 23), and acute isoncotic extracellular volume expansion (EXP, n = 15). Proximal tubular flow was perturbed in free-flowing nephrons with a microperfusion apparatus. Flow rate (VM) was measured upstream from the perturbation (VH) by a noninvasive optical technique. The dependence of VM on VH was estimated by polynomial regression. By using fractional compensation (C = -dVM/dVH), as an index of homeostatic efficiency, we constructed efficiency profiles (C vs. VH). At VH = 0, C tended toward higher values with decreasing volume status, although the effect did not achieve significance. The maximum value of C did not differ between groups. The efficiency profiles shifted leftward with each increment in volume (P < 0.03, HYD vs. EXP), suggesting that the TGF system adapts to acute increments in volume by shifting the efficiency profile in favor of a vasodilatory role.
Endothelium-derived NO stimulates pressure-dependent renin release in conscious dogs
Authors: Persson P. B. , Baumann J. E. , Ehmke H. , Hackenthal E. , Kirchheim H. R. , Nafz B.
Published: December 2017

The effect of blocking the formation of endothelium-derived relaxing factor/nitric oxide (EDNO) on pressure-dependent renin release (RR) was studied in six conscious foxhounds with chronically implanted catheters in the abdominal aorta and the renal vein. Renal blood flow (RBF) was measured with an ultrasonic transit-time flowmeter. RR was determined by multiplying the renal venous-arterial plasma renin activity difference with renal plasma flow. Renal artery pressure (RAP) was reduced in steps by a pneumatic occluder placed around the suprarenal abdominal aorta. A dose of 1,000 mg NG-nitro-L-arginine methyl ester (L-NAME) was given as a bolus to inhibit EDNO formation. In response to L-NAME, RAP increased (98 +/- 3 vs. 128 +/- 3 mmHg; P < 0.05), heart rate decreased (88 +/- 7 vs. 51 +/- 5 beats/min; P < 0.05), RBF decreased (280 +/- 19 vs. 185 +/- 24 ml/min; P < 0.05), and RR decreased (62 +/- 11 vs. 28 +/- 7 U; P < 0.05), whereas glomerular filtration rate changed little (38 +/- 3 vs. 35 +/- 4 ml/min; not significant). Below roughly 90 mmHg, RR was considerably attenuated by L-NAME as RAP was reduced in steps. At the lowest RAP (50 mmHg) RR was 1,946 +/- 406 U during control vs. 697 +/- 179 U after L-NAME (P < 0.05). Thus L-NAME inhibited pressure-dependent RR. This was especially pronounced in the low-pressure range.
Enhanced renal IGF-I expression following partial kidney infarction
Authors: Rogers S. A. , Miller S. B. , Hammerman M. R.
Published: December 2017

Renal insulin-like growth factor (IGF)-I expression is enhanced in tissue that remains following removal of kidney mass. To characterize the expression of renal IGF-I after reduction of kidney mass by partial unilateral infarction, we measured levels of IGF-I extracted from noninfarcted (remnant) renal tissue that remained after one-half unilateral kidney infarction that was performed without (1/2NX) or with (1 1/2NX) contralateral nephrectomy. Levels of IGF-I extracted from remnant renal tissue after 1/2NX increased significantly, peaking on day 3 after renal mass reduction, and then returned toward baseline. Steady-state levels of IGF-I mRNA were also elevated on day 3, suggesting that the increase in IGF-I results from enhanced synthesis. A similar pattern of increased extracted IGF-I and elevated IGF-I mRNA occurred after 1 1/2NX. Levels of IGF-I extracted from remnant renal tissue 3 days after 1 1/2NX were not higher than levels extracted from remnant tissue 3 days after 1/2NX, and both were higher than levels of IGF-I extracted from contralateral kidneys 3 days after unilateral nephrectomy. Therefore, levels of IGF-I did not correlate with the extent of reduction of renal mass per se. We conclude that partial renal infarction provides a stimulus to enhance IGF-I expression. Increased renal IGF-I must be considered in the interpretation of findings originating from use of remnant kidney models of chronic renal failure.
Developmentally regulated kallikrein enzymatic activity and gene transcription rate in maturing rat kidneys
Authors: el-Dahr S. S. , Yosipiv I.
Published: December 2017

Kinins are paracrine vasoactive and growth-modulating peptides. Kidney maturation is accompanied by enhanced accumulation of the mRNA encoding tissue (renal) kallikrein, a serine protease, and a key component of the kallikrein-kinin system. To further delineate the developmental regulation of renal kallikrein, we measured tissue kallikrein activity and gene transcription rate during the latter stages of metanephrogenesis. Active tissue kallikrein was measured in renal homogenates by the amidolytic assay using the fluorogenic substrate D-Val-Leu-Arg-7-amino-4-methylcoumarin (D-VLR-AMC) in the presence or absence of soybean trypsin inhibitor (SBTI). Kallikrein activity was detectable at very low levels in the near-term fetal metanephros. Postnatally, renal kallikrein activity peaked immediately after birth and again at the time of weaning (P < 0.05 vs. other age groups) and remained high in the adult. Mature female rat kidneys contained 30% more active kallikrein than male kidneys (P < 0.05). The SBTI-sensitive D-VLR-AMC hydrolytic activity (due to serine proteases other than tissue kallikrein) accounted for 36-53% of the total renal amidolytic activity. Compared with the 5-day-old newborn, steady-state renal kallikrein mRNA levels increased threefold by day 12 and sixfold by adulthood. Run-on transcription analysis of renal cell nuclei revealed a significant increase in kallikrein gene transcription rate of 80% on day 12 (P < 0.05) and 480% in the adult (P < 0.001). The presence of active kallikrein in the developing kidney and the upregulation of its synthesis at specific time points during postnatal development implicate intrarenal kinins as potential modulators of renal growth and functional maturation.(ABSTRACT TRUNCATED AT 250 WORDS)
Vasopressin and oxytocin receptors coupled to Ca2+ mobilization in rat inner medullary collecting duct
Authors: Maeda Y. , Han J. S. , Gibson C. C. , Knepper M. A.
Published: December 2017

In renal collecting duct epithelial cells, arginine vasopressin (AVP) at greater than nanomolar concentrations has been reported to transiently increase intracellular free calcium ([Ca2+]i) in a manner consistent with activation of the phosphoinositide pathway. To investigate whether any of the known neurohypophysial hormone subtypes are involved, we measured [Ca2+]i in microdissected rat terminal inner medullary collecting duct (IMCD) using fura-2. To allow quantitative comparisons of the response under different conditions, we determined the areas under the response curves (in nM.min) over 1.5 min using numerical integration. AVP, the V1b-receptor agonist [deamino1,D-3-(pyridyl)Ala2,Arg8]vasopressin, the V2-receptor agonist 1-desamino-8-D-arginine vasopressin, oxytocin, and the selective oxytocin-receptor agonist [Thr4,Gly7]oxytocin (TG-OXT), each at 10 nM, significantly increased [Ca2+]i (69.52 +/- 10.25, 27.0 +/- 11.7, 24.33 +/- 5.83, 14.75 +/- 2.81, and 14.57 +/- 3.50 nM.min, respectively). In contrast, a V1a-selective agonist ([Phe2,Ile3,Orn8]vasopressin) did not increase [Ca2+]i (0.43 +/- 2.36 nM.min). In desensitization studies, challenge with 10 nM AVP or TG-OXT completely prevented a rise in [Ca2+]i in response to immediate rechallenge with the same agent, but not the other, demonstrating homologous desensitization. The lack of cross-desensitization implies that at least two receptors are present that can trigger a rise in [Ca2+]i in response to neurohypophysial hormones. Antagonists for oxytocin ([des-glycinamide9,d(CH2)5(1),O-Me-Tyr2,Thr4,Orn8]vaso tocin), V2 ([d(CH2)5(1),D-Ile2,Ile4,Arg8]vasopressin), and V1a ([d(CH2)5(1),O-Me-Tyr2,Arg8]vasopressin) receptors partially inhibited the [Ca2+]i response induced by 10 nM AVP (89.5, 81.6, and 51.4% inhibition, respectively). These data are consistent with the view that both an oxytocin receptor and a vasopressin receptor are coupled to a [Ca2+]i mobilization response in rat terminal IMCD. This vasopressin receptor is distinct from both the V1a receptor and the V2 receptor and may be either the V1b receptor or a novel vasopressin receptor subtype.
V2-like vasopressin receptor mobilizes intracellular Ca2+ in rat medullary collecting tubules
Authors: Champigneulle A. , Siga E. , Vassent G. , Imbert-Teboul M.
Published: December 2017

Cytosolic free calcium concentration ([Ca2+]i) was measured in single microdissected rat medullary collecting tubules [outer (OMCD) and inner (IMCD)] to identify receptors involved in vasopressin (AVP)-induced [Ca2+]i increases. In both segments, [Phe2,Orn8]vasotocin ([Phe2,Orn8]VT), a specific V1 agonist, as well as the V2 agonist 1-desamino-8-D-AVP (dDAVP) triggered [Ca2+]i variations. In OMCD, the mean response to 10 nM AVP roughly corresponded to the sum of V1 and V2 agonists effects. In IMCD, dDAVP (10 nM) alone reproduced the calcium response to AVP (delta[Ca2+]i = 243 +/- 34 nM, n = 6, and 248 +/- 27 nM, n = 8, with dDAVP and AVP, respectively). Furthermore, in the same experiments V1 and V2 maximal effects were not additive ([Phe2,Orn8]VT = 154 +/- 21 nM, n = 6; dDAVP + [Phe2,Orn8]VT = 233 +/- 23 nM, n = 9). As AVP, dDAVP released intracellular calcium (delta[Ca2+]i in calcium-free medium = 182 +/- 24 nM, n = 8, vs. 182 +/- 14 nM, n = 6 with 10 nM dDAVP and AVP, respectively). Neither 8-(4-chlorophenyl-thio)-adenosine 3',5'-cyclic monophosphate nor forskolin modified [Ca2+]i. A cross-reaction of dDAVP with an oxytocin (OT) receptor can be excluded since 1) the specific OT agonist [Thr4,Gly7]OT (10 nM) increased only slightly [Ca2+]i (delta-[Ca2+]i = 20 +/- 5 nM, n = 11); 2) the dDAVP response was not altered by the specific OT antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid),2-(O-methyl)tyrosine,4-threonine, 8-ornithine,9-tyrosylamide]vasotocin [d(CH2)5(1),O-Me-Tyr2,Thr4,Tyr-NH2(9)]OVT; 3) it was insensitive to V1 antagonists but was totally blocked by the V1/V2 antagonist [d(CH2)5(1),O-Et-Tyr2,Val4]AVP ([delta[Ca2+]i = 18 +/- 4 nM, n = 6). These results indicate that in IMCD AVP increases [Ca2+]i via both V1 and V2 receptors. [Ca2+]i variations due to V2 receptors involve a mechanism independent of adenylate cyclase and coupled to the same intracellular calcium pool as V1 and V2 receptors.
Ion concentration changes in renal cells during regulatory volume decrease
Authors: Rick R.
Published: December 2017

Electron-probe microanalysis was employed to follow ion concentration changes during regulatory volume decrease. The measurements were performed on isolated tubule bundles, which were dissected from medullary rays of New Zealand White rabbit kidneys. Cell swelling and subsequent regulatory volume decrease were induced by incubating the bundles in 190 mosM medium; control bundles were incubated in 290 mosM medium. Under both conditions, the detectable ions accounted for approximately 80% of the intracellular osmolarity. All cells lost significant amounts of Na, K, and Cl during cell volume regulation. While in the proximal straight tubule more than one-half of the ions lost were Na and Cl, in principal and intercalated cells of the cortical collecting duct and in the thick ascending limb the losses of Na and Cl played only a minor role. The efflux of Na and K greatly exceeded the Cl efflux, suggesting the loss of an additional undetectable anion (bicarbonate). Separate measurements in the nucleus, cytoplasm, and several cellular organelles revealed some inhomogeneity of the subcellular ion distribution.
Stimulation of basolateral Na(+)-HCO3- cotransporter by angiotensin II in rabbit renal cortex
Authors: Eiam-Ong S. , Hilden S. A. , Johns C. A. , Madias N. E.
Published: December 2017

Angiotensin (ANG) II is now recognized as a powerful direct controller of Na+ reabsorption in the proximal convoluted tubule, a property that predominantly reflects stimulation of the transepithelial NaHCO3 flux. Numerous studies have established that this effect of ANG II represents stimulation of the apical Na+/H+ exchanger, but a single microperfusion study has also suggested direct stimulation of the basolateral Na(+)-HCO3- cotransporter. We have carried out studies in basolateral membrane vesicles from rabbit renal cortex to examine directly whether ANG II exerts an independent effect on the Na(+)-HCO3- cotransporter. Preincubation of vesicles with ANG II (10(-11) to 10(-9) M) for 15 min enhanced the activity of the cotransporter, the greatest effect occurring at 10(-11) M (41 +/- 1.1%, P < 0.005). This stimulation reflected an increase in the maximal enzyme reaction velocity of the cotransporter but no change in the Michaelis constant for Na+. ANG II had no effect on Na(+)-dependent succinate transport. ANG I (10(-9) M) and ANG III (10(-10) M) also stimulated the Na(+)-HCO3- cotransporter, and captopril (10(-4) M) attenuated the ANG I stimulation by 68 +/- 3.5% (P < 0.01) but not that of ANG II and III. Saralasin (10(-11) to 10(-8) M) by itself behaved as an agonist, and its stimulation was additive to that by ANG II. The nonpeptide ANG II receptor antagonist, losartan potassium (10(-6) M), and the disulfide-reducing agent, dithiothreitol (10 mM), each by itself had no effect on the cotransporter but each markedly attenuated the ANG II effect (by 77 +/- 1.4%, P < 0.01 and 74 +/- 1.6%, P < 0.005, respectively) in accord with the view that the basolateral receptor belongs to subtype 1. These results identify physiological concentrations of ANG II as a potent, direct, and specific stimulator of the basolateral Na(+)-HCO3- cotransporter.
Vascular interactions of prostaglandins with thromboxane in kidneys of rats developing hypertension
Authors: Chatziantoniou C. , Arendshorst W. J.
Published: December 2017

We investigated the ability of the vasodilator prostaglandins E2 (PGE2) and I2 (PGI2) to counterbalance the vasoconstrictor action of thromboxane A2 (TxA2) in the rat renal vasculature during hypertension. In vivo measurements of renal blood flow (RBF) were made in 6-wk-old anesthetized spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats pretreated with indomethacin. The stable TxA2 agonist U-46619 was injected into the renal artery, and the magnitude and the kinetic parameters of the renal response were evaluated before and after continuous intrarenal infusion of a low dose of PGE2, viprostol (PGE2 analogue), PGI2, and iloprost (PGI2 analogue). The selected dose of vasodilator PGs did not affect arterial pressure and RBF. In the control period, the TxA2 agonist reduced RBF by 30% with a 90-s half time of recovery in both strains. Infusion of vasodilator PGs in young WKY significantly blunted the maximum vasoconstrictor effect of the TxA2 agonist and facilitated the recovery from vasoconstriction. In marked contrast, infusion of the vasodilator PGs in young SHR failed to affect the magnitude of the vasoconstrictor effect of the TxA2 agonist, although the recovery from vasoconstriction was facilitated as in WKY. On the other hand, infusion of bradykinin or dibutyryladenosine 3',5'-cyclic monophosphate (dibutyryl cAMP) blunted the TxA2-induced vasoconstriction to a similar degree in both strains.(ABSTRACT TRUNCATED AT 250 WORDS)