bluuebunny/crossref_metadata_2025 huggingface dataset:
Does lithium clearance reflect distal delivery in humans? Analysis with furosemide infusion
Authors: Dorhout Mees E. J. , Beutler J. J. , Boer W. H. , Koomans H. A.
Published: December 2017

Fractional excretion of lithium (FELi+) has been proposed as an index of fluid delivery to the distal nephron. The increase in FELi+ after the "loop diuretic" furosemide indicates that this postulate may not be valid unless furosemide acts in the proximal tubules. We studied the effect of furosemide (40 mg iv as bolus, followed by 20 mg/h infusion for 90 min) in eight healthy male subjects during maximal water diuresis. Special care was taken to exactly replace urinary losses. Furosemide greatly increased fractional excretion of sodium, from 1.3 +/- 0.4 to 27.8 +/- 3.9%, and water, from 14.2 +/- 1.7 to 38.2 +/- 3.7% (P less than 0.01). There was a disproportionately large increase in FELi+ from 30.3 +/- 3.0 to 53.7 +/- 2.9% (P less than 0.01), whereas fractional excretion of some other alleged proximal markers increased to a lesser extent. Lysine vasopressin, infused at the end of the experiment (n = 7), caused only a small increase in urine osmolality from 225 +/- 17 to 241 +/- 17 mosmol/kg (P less than 0.01), indicating that medullary hyperosmolality had been largely abolished. The most likely explanation of these results is that furosemide has a moderate action in the proximal tubules, and at the same time inhibits preexistent lithium absorption in Henle's loop. In addition, the large difference between FELi+ and maximal urine flow remaining after furosemide suggests that, despite the decreased medullary osmotic gradient, water backdiffusion is unaltered by furosemide or that lithium concentration in the proximal tubule is changed by furosemide.
Regulation of renal transport processes and hemodynamics by macrophages and lymphocytes
Authors: Schreiner G. F. , Kohan D. E.
Published: December 2017

Inflammatory diseases of the renal glomerulus and interstitium are characterized by numerous alterations in renal glomerular hemodynamics and tubule transport processes. The cellular mechanisms underlying these changes have been theoretically attributed to nephron toxicity and destruction. However, recent studies suggest that many of the alterations in renal physiology may be mediated by specific immune cell-derived factors. Macrophages release a variety of cytokines on activation. One of these monokines, interleukin 1, induces a natriuresis by direct inhibition of collecting duct sodium reabsorption. Glomerular macrophages release highly vasoconstrictive compounds, including leukotriene D4 and thromboxane A2. Macrophages have now been demonstrated to migrate into the renal interstitium in diseases not previously considered to have an immunological component. Acute ureteral obstruction is characterized by a rapid infiltration of macrophages and lymphocytes into the kidney. Removal of the immune cell infiltrate in ureteral obstruction by irradiation markedly improves glomerular filtration rate and renal blood flow and partially corrects sodium and water excretion. Such immune modulation of renal function is likely to occur in a wide variety of diseases of the kidney, many of which do not involve a primary immunological insult. We propose that the abnormalities in renal hemodynamics and in the transport of fluid and electrolytes observed in states characterized by coexistence of immune cells among renal parenchymal cells may reflect a complex immune modulation of renal cell physiology.
Effect of ions on binding of the thiazide-type diuretic metolazone to kidney membrane
Authors: Tran J. M. , Farrell M. A. , Fanestil D. D.
Published: December 2017

The effect of a number of ions on the binding of the thiazide-type diuretic metolazone (MTZ) to rat renal cortical membranes was studied to elucidate the mechanism of NaCl transport in the kidney distal tubule. Among the cations tested, Na+ significantly stimulated the binding up to 2.4-fold over control. The effective concentration of Na+ that produced half-maximal stimulation was 2-17 mM. Li+, K+, NH4+, Rb+, and Cs+ produced little stimulation of binding of MTZ. Several anions including Cl- inhibited binding. The inhibition of binding of MTZ by Cl- was enhanced by Na+ and Li+. Scatchard analyses revealed that 50 mM Na+ increased the affinity for binding of MTZ from a Kd = 3.56 +/- 0.15 nM to Kd = 1.32 +/- 0.11 nM. Chloride, in the presence of 50 mM Na+, competitively inhibited binding of MTZ by suppressing the affinity to Kd = 9.27 +/- 1.11 nM without changing the maximal number of binding sites (0.733 +/- 0.049 pmol/mg). A mechanism for the MTZ-sensitive NaCl transport is proposed, in which the transporter protein possesses a binding site for Na+ and a binding site for Cl-, which is also the binding site for MTZ. Na+ binds to its site and increases the affinity for Cl-/MTZ. The binding of Cl- to the transporter enables the import of Na+ and Cl- across the tubule membrane. MTZ, however, when present competes with Cl- for the binding site on the transporter and prevents the transport of Na+ and Cl-.
Oxytocin receptors from LLC-PK1 cells: expression in Xenopus oocytes
Authors: Cantau B. , Barjon J. N. , Chicot D. , Baskevitch P. P. , Jard S.
Published: December 2017

Two selective radioligands for oxytocin receptors, [3H]-[4-threonine,7-glycine]oxytocin [( 3H]-[Thr4,Gly7]OT) and 125I-[1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine, 4-threonine, 8-ornithine, 9-tyrosine amide]-oxytocin (125I-OTA), were used to characterize oxytocin receptors from two pig kidney-derived cell lines, LLC-PK1 and LLC-PK1L. [3H]-[Thr4,Gly7]OT and 125I-OTA bind with high affinity (mean Kd values of 14 and 0.06 nM, respectively) to the same population of sites on LLC-PK1 cell membranes [maximum binding (Bmax) of 100 fmol/mg membrane protein]. These sites had the expected ligand selectivity of oxytocin receptors. [3H]-[Thr4,Gly7]OT and 125I-OTA binding sites could be distinguished from V2 vasopressin receptors present on LLC-PK1 and LLC-PK1L cells on the basis of clearly different maximal capacities and ligand selectivities, different sensitivities to insulin and serum, and absence of heterologous downregulation. Oxytocin receptors from LLC-PK1 cells have no functional relationship with adenylate cyclase. [Thr4,Gly7]OT affected neither the basal adenosine 3',5'-cyclic monophosphate (cAMP) content nor the vasopressin-induced cAMP accumulation by LLC-PK1 cells. Xenopus laevis oocytes injected with LLC-PK1 cell mRNA responded to [Thr4,Gly7]OT by an increase in 45Ca2+ outflux; this effect is antagonized by a highly selective oxytocin antagonist.
Effect of specific amino acid groups on renal hemodynamics in humans
Authors: Castellino P. , Levin R. , Shohat J. , DeFronzo R. A.
Published: December 2017

The effect of specific amino acid groups on renal hemodynamics was examined in seven healthy young volunteers. Each subject received a 3-h intravenous infusion according to one of the following protocols: study 1, gluconeogenic amino acids (Arg, Gly, Pro, Cys, Met, Ser); study 2, alanine alone; study 3, branched-chain amino acids (BCAA, Leu, Ile, Val); or study 4, 0.9% saline. The rise (40-60% above base line) in total plasma amino acid concentration was similar in studies 1-3; no change was observed in study 4. During study 1, glomerular filtration rate (GFR) rose by 16% (from 98 +/- 6 to 114 +/- 8 ml.1.73 m-2.min-1, P less than 0.01), and renal plasma flow (RPF) rose by 28% (from 496 +/- 47 to 638 +/- 70 ml.1.73 m-2.min-1, P less than 0.01). After alanine (study 2) and BCAA (study 3) infusion, there was a slight, although not significant, rise in GFR and RPF; during saline infusion (study 4), GFR and RPF remained unchanged. Plasma insulin and growth hormone did not change significantly in any study protocol. Plasma glucagon rose significantly by 30% in study 1 (from 117 +/- 10 to 151 +/- 13 pg/ml, P less than 0.05) but did not change in studies 2-4. In summary, infusion of mixed gluconeogenic amino acids increases both GFR and RPF, and neither alanine nor BCAA infusion caused a consistent alteration in renal hemodynamics.
Acute effect of cyclosporin on inner medullary blood flow in normal and postischemic rat kidney
Authors: Yagil Y.
Published: December 2017

Acute cyclosporin A (CysA) nephrotoxicity has been attributed to intrarenal vasoconstriction. It has been previously demonstrated that CysA decreases whole kidney and cortical blood flow. The effect of CysA on medullary blood flow has not been adequately studied, despite the high susceptibility of structures in the renal medulla to ischemia and the common use of CysA after the kidney is subjected to transient ischemia. To determine its effects on medullary blood flow in the normal and postischemic kidney, CysA was administered acutely in anesthetized Munich-Wistar rats at doses ranging from 4 to 20 mg/kg. Total renal blood flow (TRBF) and glomerular filtration rate (GFR) were determined in normal kidneys (group 1) by standard clearance techniques before and after infusion of CysA. In animals subjected to 40-min unilateral renal ischemia (group 2) TRBF was measured with an electromagnetic flowmeter. Vasa recta blood flow was determined in both groups by fluorescence videomicroscopy. In group 1, infusion with 20 mg/kg CysA, but not with 4 or 8 mg/kg, increased renal vascular resistance (RVR) and decreased TRBF. GFR was not affected and filtration fraction increased. Vasa recta blood flow was not significantly altered. In group 2, 20 mg/kg CysA increased RVR and decreased TRBF. Vasa recta blood flow decreased significantly in the descending but not in the ascending vasa recta. These results suggest that, in the normal kidney, vasa recta blood flow in the renal medulla is not affected by acute administration of CysA, whereas in the postischemic kidney, CysA decreases blood flow preferentially in the descending vasa recta, in proportion to the decline in TRBF.
Protective effect of atrial natriuretic factor and mannitol following renal ischemia
Authors: Lieberthal W. , Sheridan A. M. , Valeri C. R.
Published: December 2017

We have examined the effect of atrial natriuretic factor (ANF) administered with and without mannitol on renal function following ischemic injury in both the isolated erythrocyte-perfused rat kidney and in the rat in vivo. ANF, administered alone after 25 min ischemia in the isolated kidney, reversed postischemic vasoconstriction but did not improve glomerular filtration rate (GFR). Mannitol alone had no effect on either renal vascular resistance or GFR. However, in isolated kidneys treated with the combination of both ANF and mannitol following reflow, GFR (0.65 +/- 0.04 ml.min-1.g-1) was markedly improved compared with GFR in the untreated ischemia group (0.20 +/- 0.04 ml.min-1.g-1) and was not different from GFR in the nonischemic controls (0.68 +/- 0.05 ml.min-1.g-1). Comparable results were obtained in studies performed in vivo. In rats subjected to 45 min ischemia, GFR (0.15 +/- 0.05 ml/min) was reduced compared with the GFR in sham-operated animals (0.95 +/- 0.07 ml/min). ANF or mannitol administered alone following ischemia and reflow did not improve GFR compared with the untreated ischemic group. However, in rats subjected to ischemia and treated with a combination of ANF and mannitol postreflow, GFR (0.69 +/- 0.10 ml/min) was 4.6-fold higher than GFR in the untreated ischemic group. Thus the combination of ANF and mannitol appear to act synergistically to improve GFR following ischemic injury.
Adverse effects of growth in the glomerular microcirculation
Authors: Daniels B. S. , Hostetter T. H.
Published: December 2017

Compensatory renal and glomerular hypertrophy accompanies the many functional and structural changes associated with a reduction in functional renal mass. Increased levels of dietary sodium supplementation ranging from deficient to 2.3% Na+ (38-fold above the minimal daily requirement for the rat) in rats with subtotal nephrectomy were associated with a progressive rise in proteinuria and renal size without any significant change in arterial pressure. To further define these relationships, groups of rats on two intermediate levels of sodium intake were studied in detail. Single-nephron filtration rate and glomerular capillary pressure were similar in subtotally nephrectomized rats fed the 0.06 and 0.46% Na+ diets. Both the volume fraction and absolute volume of periodic acid-Schiff staining mesangial lesions in the glomerulus were greater in the 0.46% Na+ group. Glomerular volume and the mean glomerular capillary radius was larger in the 0.46% Na+ group. Increased glomerular tension, as predicted by the Laplace law, may represent a final common pathway by which compensatory growth and/or glomerular hypertension result in glomerular injury.
Beta-1 adrenergic inhibition of kallikrein release from rat kidney cortical slices
Authors: Girolami J. P. , Bascands J. L. , Valet P. , Pecher C. , Cabos G.
Published: December 2017

Renal storage; release, and biosynthesis of kallikrein were studied using rat cortical slices. This model permitted the study of the direct effect of norepinephrine on the renal kallikrein system in the absence of changes in perfusion pressure. Kallikrein was measured by its kininogenase activity and its direct immunoreactive concentration. Under basal conditions, rat kidney cortical slices synthesize and release glandular kallikrein in vitro at a linear rate for up to 40 min. Kidney slices obtained from rats fed with a low-sodium diet (LS) released more kallikrein into the incubation medium than slices from rats under a normal-sodium diet (NS). Cycloheximide and incubation at 4 degrees C inhibited the release and the biosynthesis of kallikrein independently of the sodium diet. Addition of norepinephrine (NE, 10(-8)-10(-5) M) induced a similar dose-dependent inhibition of kallikrein secretion, which reached -27 +/- 8% in NS rats and -29 +/- 9% in LS rats with 10(-7) M NE. This inhibition of the secretion was associated with an increase in tissue kallikrein concentration in kidney slices from rats on both sodium diets. However, a significant inhibition of the calculated net de novo synthesis was only observed in LS rats. In both groups of animals the ratio of active to total kallikrein was unchanged. The inhibitory effect of kallikrein secretion by NE was never modified in the presence of the alpha-antagonist phentolamine (10(-6) M). In contrast the beta-antagonist propranolol (10(-6) M) prevented the inhibitory effect of 10(-7) M NE.(ABSTRACT TRUNCATED AT 250 WORDS)
Decline of erythropoietin formation at continuous hypoxia is not due to feedback inhibition
Authors: Eckardt K. U. , Dittmer J. , Neumann R. , Bauer C. , Kurtz A.
Published: December 2017

Serum erythropoietin (EPO) levels in response to hypoxia are known to decline before an increase in blood oxygen carrying capacity. To define the possible mechanisms underlying this phenomenon, we have investigated 1) how renal EPO mRNA content and EPO production rate underlying the early kinetics of serum EPO levels change under different degrees of normobaric hypoxia, and 2) if a feedback inhibition of either EPO formation or EPO survival in the circulation exists by the hormone itself. We found that serum immunoreactive EPO levels in rats peaked after 12-h exposure to 7.5 or 9% oxygen (2,949 +/- 600 and 756 +/- 108 mU/ml, respectively, mean +/- SE) and declined to 29 and 64% of peak levels, respectively, after 36 h of hypoxia. EPO levels in response to 11.5% oxygen showed no consistent change between 12 (122 +/- 21 mU/ml, mean +/- SE) and 36 h (182 +/- 35 mU/ml) of hypoxia. The decline in EPO levels under severe hypoxia (7.5% O2) was paralleled by a marked reduction in renal EPO mRNA content, indicating that it was primarily a result of diminished hormone production. The observed reductions in serum EPO after 36 h corresponded to preceding declines of calculated EPO production rates from 163- to 62-fold (7.5% O2) and 36- to 25-fold (9% O2) basal values. Application of 50 IU recombinant human EPO to rats 12 h, 6 h, or immediately before hypoxic exposure to mimic the early increase in EPO levels did not affect endogenous EPO formation during a subsequent hypoxic exposure of 12 h.(ABSTRACT TRUNCATED AT 250 WORDS)
Physiological features of edematous dogs unresponsive to atrial natriuretic peptide
Authors: Maher E. , Cernacek P. , Levy M.
Published: December 2017

Sodium-retaining cirrhotic and chronic caval dogs with ascites show a heterogeneous natriuretic response to atrial natriuretic factor (ANF) infusions such that half will increase their urinary excretion of sodium and half will show no natriuretic response whatsoever. In these studies we have examined several physiological variables that might discriminate between these two experimental populations. We studied 22 caval dogs (11 natriuretic responders, 11 nonresponders) and 19 cirrhotic dogs (9 responders, 10 nonresponders). After an infusion of rat ANP-(1-28), 125 ng.kg-1.min-1, differences in glomerular filtration rate, blood pressure, or urinary excretion of guanosine 3',5'-cyclic monophosphate (cGMP) could not differentiate between the two types of dogs. When the left kidney of nonresponding dogs in both the caval and cirrhotic groups was either denervated or vasodilated with acetylcholine bromide (60-80 micrograms/min), the attenuation of the natriuretic response to ANF was not reversed. Papillary plasma flow (PPF) after ANF infusion was measured by a Lillienfield technique and averaged 36 +/- 4 ml.min-1.100 g-1 in normal dogs, 10.7 +/- 0.7 ml.min-1.100 g-1 in both responding and nonresponding caval dogs, and 48.3 +/- 1.1 ml.min-1.100 g-1 for each group of cirrhotic dogs. We conclude that differences in renal perfusion, PPF, cGMP generation, or the presence of intact renal nerves cannot explain the lack of a post-ANF natriuretic response in half of caval or cirrhotic dogs. Other physiological determinants must explain the heterogeneity of natriuretic response to ANF observed in edematous dogs.
Platelet-activating factor is a renal vasodilator in the anesthetized rat
Authors: Handa R. K. , Strandhoy J. W. , Buckalew V. M.
Published: December 2017

In view of the potent vasoactive properties of platelet-activating factor (PAF), we investigated the renal hemodynamic effects of this lipid. C16-PAF (0.5-10 ng/kg) given as a bolus into the renal arterial circulation of pentobarbital sodium-anesthetized male Wistar rats produced a dose-dependent increase in renal blood flow (6-15%), before causing systemic hypotension. The PAF-induced renal vasodilation and systemic hypotension was independent of renal innervation, unaltered by eicosanoid synthesis inhibition with indomethacin or dexamethasone, unchanged by the nonselective dopamine-receptor antagonist haloperidol, but was abolished by the PAF-receptor antagonist, L-659,989. Non-hypotensive intrarenal PAF infusion at 0.5 ng.min-1.kg-1 caused an increase in renal blood flow. Thus PAF can cause renal vasodilation in the rat kidney that is PAF-receptor mediated and does not involve the sympathetic nervous system or the release of vasodilatory arachidonic acid metabolites or dopamine.
Renal norepinephrine spillover and baroreflex responses in evolving heart failure
Authors: Sano N. , Way D. , McGrath B. P.
Published: December 2017

Renal sympathetic nerve activity (RSNA), as assessed by norepinephrine (NE) spillover, was examined in conscious rabbits with adriamycin-induced cardiomyopathic heart failure (n = 5) and in control rabbits (n = 5). Each rabbit was studied after 4 and 6 wk of adriamycin (2 mg.kg-1.wk-1) or vehicle under resting conditions and in response to changes in mean arterial pressure (MAP) produced by infusions of sodium nitroprusside and phenylephrine. Basal renal NE spillover rate was significantly increased after 4 wk of adriamycin treatment compared with controls (24.2 +/- 2.5 vs. 15.2 +/- 2.4 ng/min, P less than 0.05). At this stage the two groups had similar systemic hemodynamics and renal blood flows. The baroreflex-renal NE spillover response to hypotension in the adriamycin-treated group showed a significant upward shift. After 6 wk of adriamycin treatment, there were significant falls in resting MAP (74 +/- 3 vs. 86 +/- 2 mmHg, P less than 0.01) and renal blood flow (78 +/- 6 vs. 109 +/- 8 ml/min, P less than 0.05). At this stage of established heart failure, resting renal NE spillover rate remained elevated but there was significant blunting of the baroreflex-renal NE spillover response. These results suggest that, in this model of low-output heart failure, there is an early increase in resting renal sympathetic activity that is sustained. The baroreflex-renal NE spillover curve changes during the course of development of heart failure.
Kinins inhibit conductive Na+ uptake by rabbit inner medullary collecting duct cells
Authors: Zeidel M. L. , Jabs K. , Kikeri D. , Silva P.
Published: December 2017

Kinins promote natriuresis in vivo, at least in part by altering Na+ transport in the collecting duct. Using freshly prepared suspensions of rabbit inner medullary collecting duct (IMCD) cells, we have examined the effects of kinins on Na+ transport using measurements of oxygen consumption (QO2) and isotopic Na+ uptake. Bradykinin (BK) inhibited IMCD cell QO2 by 24.7 +/- 0.9% without significantly reducing QO2 in cells derived from the outer medullary collecting duct. BK and kallidin half-maximally inhibited QO2 at concentrations in the 10(-12)-10-(-11) M range; beta 1-receptor agonists did not alter QO2, and beta 1-receptor antagonism did not reduce the effect of kinins. These observations indicate that the actions of kinins on IMCD cells are mediated by beta 2-receptors or a distinct subclass. Several observations indicate that kinins reduce QO2 by inhibiting Na+ entry: in the absence of Na+, BK did not reduce QO2; BK inhibition of QO2 was not additive with ouabain, amiloride, atrial natriuretic peptide (ANP), or 8-bromoguanosine 3',5'-cyclic monophosphate and was abolished in the presence of the cation ionophore amphotericin B. Measurements of isotopic Na+ uptake demonstrated that BK reduced the initial rate of Na+ entry by 58%; BK inhibited the amiloride-sensitive component of conductive Na+ uptake. Because ANP inhibits conductive Na+ entry in IMCD cells via stimulation of cGMP accumulation, the effect of BK on cGMP levels was determined. Unlike ANP, BK did not increase cGMP levels, indicating that transport effects of kinins in IMCD are not mediated by cGMP. Thus kinins directly inhibit conductive Na+ entry in IMCD cells at concentrations suggestive of a physiological effect.(ABSTRACT TRUNCATED AT 250 WORDS)
Cadmium inhibits glucose uptake in primary cultures of mouse cortical tubule cells
Authors: Blumenthal S. S. , Lewand D. L. , Buday M. A. , Kleinman J. G. , Krezoski S. K. , Petering D. H.
Published: December 2017

We studied the effect of cadmium (Cd2+) on transport of alpha-methylglucoside in primary cultures of mouse kidney cortical tubule cells grown in defined medium. When cultured cells were exposed to Cd2+ concentrations from 0 to 6 microM for 24 h, uptake of alpha-methylglucoside was inhibited in a dose-dependent manner by up to 50%. By contrast, acute exposure of the cells to 7 microM Cd2+ for 60 min did not inhibit alpha-methylglucoside uptake. Increasing Cd2+ concentrations progressively decreased the Vmax of Na(+)-dependent glucose cotransport but not the Km for glucose. Cell ATP/ADP ratios of unexposed monolayers and of cells exposed to 4.5 microM Cd2+ for 24 h were 5.0 and 4.9, respectively (n = 3). Intracellular volume, lactate dehydrogenase activity, and cell Na+ and K+ concentrations were unaltered even after 24 h of exposure to 7 microM Cd2+. Untreated and Cd2+-treated monolayers preloaded with alpha-methylglucoside released the sugar analogue into the medium at nearly identical rates, indicating that Cd2+ did not alter cell permeability to glucose. Uptake of the amino acid analogue alpha-(methylamino)isobutyric acid was not affected by prior Cd2+ exposure. Whereas cell DNA content declined in Cd2(+)-exposed plates, both Na(+)-glucose and Na(+)-amino acid cotransport were enhanced at lower cell densities. Protein and DNA synthesis, estimated, respectively, by incorporation of [3H]leucine and [3H]thymidine into acid-insoluble material, were not significantly affected at 6 microM Cd2+. We conclude that after a lag time Cd2+ selectively inhibits renal Na(+)-dependent glucose transport despite an unchanged gradient for Na+ across the cell membrane.
Uncoupling of glomerular and tubular regulations of urea excretion in rat
Authors: Peil A. E. , Stolte H. , Schmidt-Nielsen B.
Published: December 2017

Renal adjustments to diets varying in protein and sodium content were studied in young anesthetized Munich-Wistar rats. Diets were as follows: high (50%) protein (HP), normal (24%) protein (NP), reduced (8%) protein without extra salt (RPNS), and RP with extra salt (RPWS, 2.8% extra salt). Rats grew at the same rate on all diets. Glomerular filtration rate (GFR), urea, sodium, and osmolar clearances were measured. In series 1, groups of rats were maintained for 4 wk on the four diets and one group on changed diet (CP2d, RPWS diet for 4 wk changed to NP diet for 2 days). GFR was reduced compared with NP rats by 12% in RPNS and RPWS, and by 16% in CP2d rats, but the differences were not statistically significant. Fractional excretion of urea (FEurea) was significantly changed compared with NP. It was 40% higher in HP rats, and 50 and 56% lower in RPNS and RPWS, respectively. In the CP2d group it had increased to the NP value. In series 2, groups of rats were maintained on the RPNS diet for 1, 2, 3, and 4 wk, respectively. GFR decreased 21.6% after only 1 wk but after 4 wk it was not significantly lower than in the NP group. In contrast, no significant reduction was found in FEurea after 1 wk, whereas it decreased by 40% during the 2nd wk, with no further decrease after 3 and 4 wk. GFR was not directly related to protein or salt intake.(ABSTRACT TRUNCATED AT 250 WORDS)
ADH modulates plasma membrane lipid order of living MDCK cells via a cAMP-dependent process
Authors: Giocondi M. C. , Friedlander G. , Le Grimellec C.
Published: December 2017

Using 1-[4-(trimethylamino)phenyl]-6-phenyl-hexa-1,3,5-triene, a fluorescent probe that specifically labels the external leaflet of the plasma membrane of living cells, we examined the effects of antidiuretic hormone (ADH) and various agents known to raise intracellular adenosine 3',5'-cyclic monophosphate (cAMP) on the physical state of the plasma membrane of Madin-Darby canine kidney (MDCK) cells. In polarized cells grown as a monolayer, [desamino-Cys1, DArg8]-vasopressin (V2-agonist) elicited a biphasic decrease in the lipid order as estimated from the decrease in fluorescence anisotropy (from r = 0.317 to r = 0.304, 37 degrees C) of the apical domain of the plasma membrane, equivalent at the peak response (t = 5 min) to that produced by an upward shift in temperature of 5-6 degrees C. A similar response was obtained by adding dibutyryl cAMP to the monolayers. Experiments on cell suspensions further indicated that the biphasic decrease in lipid order could also be evoked by forskolin, prostaglandin E2, and bradykinin but not by bradykinin plus indomethacin and was inhibitable by the protein kinases inhibitor compound H7. These data demonstrate that the lipid order of the plasma membrane of MDCK cells can be modulated in situ by cAMP-dependent processes probably involving protein kinase A activity, i.e., that membrane “fluidity” might act in the regulation of the cellular function of living epithelial cells. They provide a rationale for the changes in lipophilic solute permeability that accompany the increase in water permeability of target cells on ADH administration.
Mechanisms of impaired insulin secretion after chronic excess of parathyroid hormone
Authors: Perna A. F. , Fadda G. Z. , Zhou X. J. , Massry S. G.
Published: December 2017

Excess parathyroid hormone (PTH) in presence or absence of chronic renal failure impairs insulin release from pancreatic islets. This abnormality has been attributed to PTH-induced accumulation of Ca in the cytosol of the islets. Direct evidence for the latter phenomenon is lacking. This study examined the effect of chronic administration of PTH to rats with normal renal function on resting cytosolic Ca of the islets and evaluated the mechanisms through which a rise in resting cytosolic Ca may inhibit insulin secretion. After 42 days of PTH administration, glucose-induced insulin secretion was impaired, and this defect was corrected by the use of D-glyceraldehyde as secretagogue for insulin. Resting cytosolic Ca of islets from PTH-treated rats was markedly increased compared with that of islets from normal animals (288 +/- 27.1 vs. 135 +/- 3.7 nM, P less than 0.01), and their content of ATP in the presence of both 2.8 and 16.7 mM D-glucose was reduced (2.8 mM D-glucose, 4.6 +/- 0.17 vs. 6.0 +/- 0.42 pmol/islet, P less than 0.01; and 16.7 mM D-glucose, 6.9 +/- 0.25 vs. 11.1 +/- 0.95 pmol/islet, P less than 0.01). D-Glyceraldehyde increased ATP content in islets of PTH-treated rats from 4.6 +/- 0.17 to 8.8 +/- 0.71 pmol/islet. Glucose uptake by the islets, their insulin content, and both the Vmax and the apparent Km for fructose 6-phosphate of phosphofructokinase 1 (EC 2.7.1.11) in PTH-treated rats were not different from normal. The two major cellular derangements in the islets of PTH-treated rats were a reduction in ATP content and a rise in resting cytosolic Ca.(ABSTRACT TRUNCATED AT 250 WORDS)
Renal expression of IGF I in hypersomatotropic states
Authors: Miller S. B. , Rotwein P. , Bortz J. D. , Bechtel P. J. , Hansen V. A. , Rogers S. A. , Hammerman M. R.
Published: December 2017

We examined insulin-like growth factor I (IGF I) gene expression in kidney in two models of hypersomatotropism, rats implanted with GH3 pituitary tumors, and rats administered exogenous growth hormone (GH). Both GH3 tumor-bearing rats and rats administered GH gained weight more rapidly than control animals, and had kidneys that were larger than those of controls. Tumor-bearing rats had increased levels of circulating IGF I. Glomeruli from tumor-implanted rats were sclerotic. Immunostainable IGF I was increased in medullary collecting ducts from tumor-bearing and GH-injected rats compared with kidneys from control animals. Levels of IGF I mRNA in kidneys of rats implanted with GH3 tumors and GH-injected rats were elevated compared with levels in kidneys from controls. Our findings demonstrate enhanced renal IGF I gene expression in hypersomatotropism. Stimulation of renal IGF I synthesis by GH could be causative of changes in renal function and renal size that occur in states of GH excess such as acromegaly.
Contribution of luminal ammoniagenesis to proximal tubule ammonia appearance in the rat
Authors: Simon E. E. , Merli C. , Herndon J. , Hamm L. L.
Published: December 2017

The contribution of luminal ammoniagenesis in the late proximal convolute tubule (PCT) via phosphate-independent glutaminase [gamma-glutamyltransferase (gamma-GT)] remains controversial. If this pathway is important, it must rely on glutamine secretion, because filtered glutamine is reabsorbed in the early PCT. The contribution of gamma-GT to luminal ammoniagenesis was tested by use of in vivo microperfusion in conjunction with a new microfluorometric assay for glutamate. We first confirmed that aspartate completely blocked glutamate uptake in the PCT. Furthermore, the gamma-GT inhibitor acivicin completely eliminated glutamate entry, showing that passive glutamate entry was negligible. Thus the accumulation of glutamate can be used as an estimate of luminal glutamine deamidation. L-Phenylalanine was used to inhibit glutamine loss, and hippurate was used to stimulate gamma-GT activity; therefore luminal glutamine conversion to glutamate was promoted. Perfusing the tubule at 30 nl/min with a solution containing 10 mM each of hippurate, phenylalanine, and aspartate resulted in a glutamate delivery of 1.08 +/- 0.12 pmol.min-1.mm-1. Ammonia appearance was 10-fold higher, averaging 11.5 +/- 1.3 pmol.min-1.mm-1 under these same conditions. Thus the luminal conversion of glutamine to glutamate via gamma-GT is a small component of total ammoniagenesis in this segment.
Effects of ANF on cGMP synthesis in inner medullary collecting duct subsegments of rats
Authors: Ujiie K. , Nonoguchi H. , Tomita K. , Marumo F.
Published: December 2017

The inner medullary collecting duct (IMCD) is thought to be a major target site for atrial natriuretic factor (ANF) action. The IMCD is divided into two subsegments (IMCD1, outer third; and IMCD2,3, inner two-thirds) based on differences in urea and water permeability. IMCD1 has similar characteristics to the outer medullary collecting duct (OMCD). To elucidate whether there are any differences among these segments in ANF actions, we investigated the effects of ANF on guanosine 3',5'-cyclic monophosphate (cGMP) synthesis in IMCD subsegments and the OMCD. We also examined the effects of arginine vasopressin (AVP) on adenosine 3',5'-cyclic monophosphate (cAMP) synthesis. IMCD subsegments (IMCD1,2,3) and OMCD were microdissected; and ANF-stimulated cGMP synthesis and AVP-stimulated cAMP synthesis were measured. cGMP synthesis stimulated by 10(-6) M ANF in IMCD1,2,3 (0.78 +/- 0.15, 0.81 +/- 0.19, 0.62 +/- 0.10 fmol.mm-1 x 3 min-1, mean +/- SE respectively, n = 10-11) was significantly (greater than 20-fold) higher than that in OMCD (0.03 +/- 0.02 fmol.mm-1 x 3 min-1, n = 7), and there was no difference among IMCD subsegments. On the other hand, cAMP synthesis stimulated by 10(-7) M AVP in IMCD subsegments was similar to that in OMCD. We conclude that IMCD is homogenous as a target site of ANF and is clearly distinguished from OMCD. In addition, more than half of ANF-stimulated cGMP synthesis in IMCD are considered to occur in IMCD1, simply because IMCD1 is dominant in population among IMCD subsegments. As target sites of AVP, IMCD subsegments are similar to OMCD.
Pathways for apical and basolateral membrane NH3 and NH4+ movement in rat proximal tubule
Authors: Preisig P. A. , Alpern R. J.
Published: December 2017

To examine the mechanism of preferential luminal ammonia secretion in the proximal tubule the apical and basolateral membrane pathways for NH3 and NH4+ movement were studied in the in vivo microperfused rat proximal tubule. Na and Cl were absent from all perfusates. Changes in pHi in response to rapid addition of NH3-NH4+ to either the luminal or peritubular perfusates were measured microfluorimetrically and expressed as the H(+)-equivalent flux (JeqH in pmol.mm-1.min-1). After ammonia addition ([NH3] 0.3 mM; [NH4+] 14.7 mM) to the luminal or peritubular fluids, pHi increased, and JeqH = 1,713 +/- 181 and 1,040 +/- 132 pmol.mm-1.min-1, respectively. To determine whether the above difference was due to NH3- or NH4(+)-driven fluxes, the effect of a fivefold greater [NH4+] ([NH3] 0.3 mM; [NH4+] 74.5 mM) on JeqH was examined. With luminal addition of a fivefold greater [NH4+], JeqH increased to 3,299 +/- 292 pmol.mm-1.min-1, demonstrating a pathway for NH4(+)-driven H+ efflux. One millimolar luminal amiloride inhibited JeqH in response to luminal NH3-NH4+ addition, suggesting that the amiloride-sensitive Na(+)-H+ antiporter mediates the NH4(+)-driven H+ efflux. JeqH was unaffected by addition of a fivefold greater [NH4+] to the peritubular perfusate, demonstrating the absence of an NH4(+)-driven H+ flux on the basolateral membrane. From these data, the calculated NH3 permeabilities were 6.2 +/- 1.3 and 7.0 +/- 0.9 X 10(-2) cm/s for the apical and basolateral membranes, respectively (NS). We conclude that apical and basolateral membrane NH3 permeabilities are similar and large. The apical membrane can also transport NH4+ on the amiloride-sensitive Na(+)-H+ antiporter.
Interaction of adenosine with vasopressin in the inner medullary collecting duct
Authors: Yagil Y.
Published: December 2017

Administration of adenosine (Ado) into rat renal artery induces dose-dependent diuresis that is independent of changes in glomerular filtration rate or renal blood flow, suggesting a direct effect on tubule H2O reabsorption. To test the hypothesis that Ado modulates cellular action of arginine vasopressin (AVP) as a tubular mechanism for the diuretic effect of Ado, interaction of Ado with AVP was studied in primary cell culture of rat inner medullary collecting duct (IMCD) epithelium. Stimulation of cells with 10(-6) M AVP in presence of 0.1 mM Ro 20-1724, a nonmethylxanthine phosphodiesterase inhibitor that has no effect on Ado receptors, increased adenosine 3',5'-cyclic monophosphate (cAMP) levels twofold or more above baseline. Stimulation of cells with the A1 Ado-receptor agonist N6-cyclohexyladenosine (CHA), the A2-receptor agonist 5'-(N-ethylcarboxamido)-adenosine (NECA), or with the P-site agonist 2',5'-dideoxyadenosine (DDA) significantly inhibited the AVP-stimulated cAMP response. Preincubation with pertussis toxin abolished the inhibitory effects of CHA and NECA, but not of DDA. The data suggest that, in the rat IMCD, Ado modulates AVP action by interfering with its ability to stimulate formation of its second messenger, cAMP. This effect is mediated by the extracellular Ado receptors A1 and A2 and by the intracellular P-site. It occurs by at least two pathways, one sensitive and the other insensitive to pertussis toxin.
Resistance of descending vasa recta to the transport of water
Authors: Pallone T. L. , Work J. , Jamison R. L.
Published: December 2017

The effect of varying intracapillary oncotic pressure on the rate of transcapillary volume flux in microperfused descending vasa recta (DVR) was studied during furosemide diuresis in the Munich-Wistar rat. At the papillary base, plasma protein concentration and hydraulic pressure were 5.7 +/- 0.1 g/dl and 11.7 +/- 0.7 mmHg in nonperfused DVR, respectively, and 5.6 +/- 0.1 g/dl and 9.4 +/- 0.4 mmHg in nonperfused ascending vasa recta (AVR), respectively. These results demonstrate that the papillary microcirculation does not remove water from the interstitium during furosemide diuresis and defines Starling forces in the pericapillary interstitium. Osmolality and urea concentration were 380 +/- 11 mosmol/kgH2O and 56 +/- 5 mM in DVR plasma at the papillary base, respectively, and 386 +/- 10 mosmol/kgH2O and 62 +/- 5 mM in DVR plasma at the tip, respectively. These results demonstrate abolition of corticomedullary small solute gradients. DVR were perfused at a rate of 10 nl/min with a buffer solution containing small-solute concentrations that matched those of plasma in nonperfused DVR. The buffer solution also contained 2 x 10(6) mol wt fluorescein isothiocyanate-labeled dextran (FITC-Dx, 5 mg/ml) and either 0.1 or 5.0 g/dl albumin. Microperfused DVR were punctured a second time downstream of the perfusion site for sample collection or servo-nulling pressure measurement. The rate of transmembrane volume flux, determined from the change in FITC-Dx concentration from perfusate to collectate, was 0.99 +/- 0.29 nl.min-1.mm-1 when perfusate contained 0.1 g/dl albumin and 0.00 +/- 0.23 nl.min-1.mm-1 with 5.0 g/dl albumin (P less than 0.01). Intracapillary hydraulic pressures were 21.7 and 20.4 mmHg during microperfusion of DVR with 0.1 and 5.0 g/dl albumin, respectively. These results demonstrate that transcapillary driving forces of 20 mmHg (5 g/dl albumin) influence transcapillary water movement across the DVR endothelium. For an average capillary diameter of 12.9 microns, DVR hydraulic conductivity is calculated to be greater than 1.4 x 10(-6) cm.s-1.mmHg-1.
Leukotrienes stimulate neutrophil adhesion to mesangial cells: modulation with lipoxins
Authors: Brady H. R. , Persson U. , Ballermann B. J. , Brenner B. M. , Serhan C. N.
Published: December 2017

We have examined polymorphonuclear neutrophil (PMN) adhesion to mesangial cells (MC) in vitro and have assessed the actions of lipoxygenase (LO) products in this process. On exposure to either leukotriene B4 (LTB4), or leukotriene D4 (LTD4), 111In-labeled PMNs adhere to monolayers of cultured MC. These actions were rapid in onset (less than 5 min) and dependent upon leukotriene concentration (10(-9) to 10(-6) M) and the presence of divalent cations. Adhesion was sustained (0-30 min), and neither LTB4 nor LTD4 was metabolized to inactive products during PMN-MC interaction, as determined by their recovery after reverse-phase high-performance liquid chromatography. LTB4 was a PMN-directed stimulus, whereas LTD4 appeared to act on MC. A monoclonal antibody (TS 1/18) against the CD18 component of the PMN CD18/CD11 adhesion complex inhibited the LTB4-induced response, indicating involvement of this PMN glycoprotein in the adhesion process. In contrast, this antibody did not affect LTD4-induced adhesion, suggesting that this response was mediated by other adhesion epitopes. When added alone, neither lipoxin A4 (LXA4) nor lipoxin B4 (LXB4) provoked PMN adhesion to MC. In contrast, LXA4 and LXB4 at equimolar concentrations attenuated the LTD4- but not LTB4-induced response. Together, these results provide further evidence that LO-derived eicosanoids may constitute important early signals that regulate PMN-MC interaction in glomerular inflammation.
Oxytocin receptors in rat kidney during development
Authors: Schmidt A. , Jard S. , Dreifuss J. J. , Tribollet E.
Published: December 2017

The development and characteristics of oxytocin (OT) receptors in the rat kidney were studied by light-microscopic autoradiography and on membrane preparations using the iodinated OT antagonist 125I-d(CH2)5[Tyr(Me)2,Thr4,Orn8,Tyr(NH2)9]OT. Specific binding was first detected by autoradiography at embryonic day 17 (E17) in both the cortex and the medulla. Cortical labeling was found thereafter at all ages examined including in the adult (postnatal day 90, PN90). It was localized on the distal tubule at the level of the juxtaglomerular apparatus. Medullary binding was detected only transiently during two stages of development, first, before PN6, and second, at the approximate time of weaning (PN20-PN30). Binding studies on crude membranes prepared from whole kidneys of animals aged between PN1 and PN15 showed a single class of high-affinity binding sites, with a dissociation constant of 0.13 +/- 0.08 nM. Thus transient OT binding sites expressed in the medulla do not differ from cortical OT binding sites; moreover, the ligand selectivity of kidney OT receptors regardless of location and age appears similar to that of previously characterized OT receptors. Our results suggest that OT may play a role in both renal development and renal function.
Renal effects of moderate hemorrhage in the conscious pregnant rat
Authors: Baylis C. , Brango C. , Engels K.
Published: December 2017

Studies were performed in conscious, chronically catheterized virgin, 8- to 9-day-pregnant, and 15- to 16-day-pregnant Sprague-Dawley rats in baseline state and after removal of 7.5% total blood volume. Measurements were made of glomerular filtration rate (GFR), renal plasma flow (RPF), renal vascular resistance (RVR), arterial blood pressure (AP), and urinary electrolyte excretion. In baseline state, GFR and RPF were elevated at days 8-9 and days 15-16 of pregnancy (vs. virgins) due to a gestational renal vasodilation. The fall in hematocrit indicates substantial plasma volume expansion by days 15-16 of pregnancy. After removal of 7.5% total blood volume, little change occurred in AP in any group. However, the renal vasculature provided a sensitive response to moderate hemorrhage, since RPF fell and RVR increased similarly in virgin, 8- to 9-day- and 15- to 16-day-pregnant rats. GFR was protected in virgin and 8- to 9-day-pregnant rats but fell significantly in late pregnancy. Urinary electrolyte excretion tended to fall but was not significantly reduced by hemorrhage in any group. These studies indicate that renal vascular response to moderate hemorrhage is similar in virgin, early, and late pregnancy. Thus effector mechanisms that sense volume and regulate RVR must be continually reset to respond to progressive plasma volume expansion of pregnancy as normal.
Ontogeny of DA1 receptor-adenylate cyclase coupling in proximal convoluted tubules
Authors: Kinoshita S. , Felder R. A.
Published: December 2017

The natriuretic effect of dopamine (DA) is less in younger than in older animals. The natriuretic (DA) is less in younger than in older animals. The natriuretic effect of DA is due in part to occupation of renal tubular DA1 receptors, which are most abundant in the proximal convoluted tubule (PCT). However, it has not been determined whether ontogenic differences in DA1-receptor density, affinity, or coupling to intracellular second messengers are involved in the reduced natriuretic effect of DA in the young animal. We therefore studied the DA1 receptor by radioligand binding with the DA1 antagonist 125I-SCH 23982 and the effect of DA1 agonists and guanine nucleotides on adenylate cyclase (AC) activity in microdissected PCT during development in Wistar-Kyoto rats (WKY). The dissociation constant (Kd) and maximum receptor density (Bmax) were similar in all groups (Kd, in nM: 11.9 +/- 0.7 at 3 wk, 10.6 +/- 0.4 at 8 wk, and 12.2 +/- 1.2 at 20 wk; Bmax, in fmol/mm PCT: 0.24 +/- 0.02 at 3 wk, 0.23 +/- 0.01 at 8 wk, and 0.24 +/- 0.01 at 20 wk). Basal AC activities were similar, and forskolin (10(-5) M), which directly stimulates AC, increased AC activity to a similar extent in all age groups. However, the DA1 agonists, fenoldopam (10(-5) M) and SND-919-CL2 (10(-6) M), increased AC activity in PCT to a greater extent in 20-wk-old (55 +/- 7%) than in 3-wk-old rats (27 +/- 1%).(ABSTRACT TRUNCATED AT 250 WORDS)
Basolateral transport pathways for K+ and Cl- in rabbit proximal tubule: effects on cell volume
Authors: Schild L. , Aronson P. S. , Giebisch G.
Published: December 2017

To characterize the nature of K+ and Cl- transport pathways across basolateral membrane of rabbit proximal convoluted tubule, we used quantitative video microscopy to measure cell volume changes induced by rapid basolateral K+ and Cl- concentration changes. Elevating basolateral K+ resulted in cell swelling, which was largely inhibited by replacement of basolateral Cl- with cyclamate (85%) or by addition of 2 mM Ba2+ (72%). Substitution of basolateral Cl- by NO3- enhanced cell swelling, whereas substitution of Cl- by I- did not affect the K(+)-induced volume changes. Removal of Cl- from the bath reversed the cell swelling induced by raising K+ in the bath. Steady-state cell volume was 28% greater in hypotonic medium (250 mosmol/kgH2O) than in hypertonic medium (350 mosmol/kgH2O), and the rate of increase in cell volume induced by raising K+ was three times higher in hypotonic than in hypertonic medium. Substitution of Cl- by NO3- did not alter the effect of medium osmolality on K(+)-induced cell swelling, whereas addition of 0.2 mM diphenylamine-2-carboxylate inhibited the response (63%). We conclude that K(+)-induced cell swelling results from entry of K+ and Cl- into the cell across the basolateral membrane; it is proposed that transport of KCl across the basolateral cell membrane proceeds largely through two separate conductive pathways for K+ and Cl-. Cell swelling activates KCl transport occurring via K+ and Cl- channels across the basolateral membrane.