bluuebunny/crossref_metadata_2025 huggingface dataset:
Urinary concentrating defect in the aged rat
Authors: Bengele H. H. , Mathias R. S. , Perkins J. H. , Alexander E. A.
Published: December 2017

The renal concentrating ability of Fischer 344 rats was studied at 23 and 4 mo of age. Maximum urine concentration after 40 h of dehydration with or without vasopressin injection was significantly lower (P less than 0.01) in old (2,550 +/- 70 and 2,363 +/- 107 mosmol/kg H2O2, respectively) vs. young (3,242 +/- 50 and 3,162 +/- 50 mosmol/kg H2O, respectively) rats. Free water reabsorption (TcH2O/GFR) rose progressively as a function of osmolar clearance, and at similar values of distal solute delivery TcH2O was clearly reduced in the old group. Free water formation (CH2O/GFR) rose linearly as a function of urine flow and was not different between old and young rats. Glomerular filtration rate was also not different between age groups under the conditions studied. Nonurea (sodium + potassium + ammonium) x 2 and urea solute concentrations as well as total calculated osmolality in the cortex, outer medulla, or inner medulla were not different between age groups. Because the indices of ascending limb solute delivery and transport and the solute gradient for water reabsorption were similar, we conclude that the concentrating defect in aged rats is most likely secondary to a decrease in water permeability along the collecting duct.
Hypo- and hyperosmolal saline and raffinose on kidney cortical cell volume at 37 degrees C
Authors: Gyory A. Z. , Kweifio-Okai G. , Ng J.
Published: December 2017

Cell water content was measured in respiring rat renal cortical slices incubated in hypo- and hyperosmolal saline with and without raffinose and ouabain for 60 min at 37 degrees C. At 60 min, hyposmolal saline (228 mosmol/kg H2O) caused a 16% swelling of cells, whereas addition of 73 mM raffinose (299 mosmol/kg H2O) caused a 33% shrinkage. Physiological saline plus raffinose (364 mosmol/kg H2O) caused a 28% cell shrinkage, whereas addition of saline (385 mosmol/kg H2O) produced only a 10% decrease in cell volume. The effects of raffinose were reversible. At physiological Na concentrations, osmole for osmole raffinose was 4 times as effective in shrinking cells as saline, but only 2 times as effective at Na of 112 mM. Osmotic effectiveness of saline changed, that of raffinose did not. Ouabain caused no changes in cell volume and did not prevent the effect of raffinose. In conclusion, there is no volume regulation to nonelectrolyte solutes and only partial volume regulation to saline, and this is due to differential osmotic effects of these solutes, that of saline decreasing from low to high Na.
Stoichiometry and coupling of active transport to oxidative metabolism in epithelial tissues
Authors: Mandel L. J. , Balaban R. S.
Published: December 2017

A linear relationship has been observed between the rate of active ion transport and the oxygen consumption or lactate production rate in a variety of epithelia. Stoichiometries of ions transported per oxygen consumed or ATP utilized calculated from these relationships reflect actual properties of the active transport step when the following two conditions are met: 1) the basal metabolic rate, obtained in the absence of active transport, remains constant at all rates of active transport; and 2) all the net transport across the tissue considered in the calculation traverses through active (energy-dissipative) pathways. The nature of the cellular mechanism linking active transport and energy production is a fundamental physiological question. Experimental alterations in the rate of active transport elicit mitochondrial state transitions and/or changes in adenine nucleotide concentrations in various epithelia. These findings, obtained by optical and biochemical methods, indicate that ATP and its hydrolysis products constitute part of the coupling mechanism linking the turnover of transport ATPase and the aerobic metabolic rate in epithelia.
Basis for heterogeneity of para-aminohippurate secretion in rabbit proximal tubules
Authors: Shimomura A. , Chonko A. M. , Grantham J. J.
Published: December 2017

Para-aminohippurate (PAH) is secreted at different rates in S1, S2, and S3 segments of isolated perfused proximal tubules of rabbit kidney. To characterize PAH transport we determined the maximal rate of secretion (Vmax) and the apparent Michaelis constant (Km) for each segment by examining the relationship between bath concentration of PAH and net PAH secretion (Jb leads to lPAH) transposed for Lineweaver-Burk analysis. The passive component of secretion for all segments was estimated by slope analysis at relatively high concentrations of PAH, by the component of PAH secretion insensitive to inhibition by probenecid, and, additionally, in S2 segments, from PAH efflux from lumen to bath. Subtraction of the passive component from Jb leads to lPAH (probenecid method) gave Vmax values for S1, S2, and S3 segments of 1,097 +/- 336 (n = 6), 7,430 +/- 1,338 (n = 6), 1,647 +/+ 138 (n = 8) X 10(-15) mol.min-1.mm-1 (+/- SE) and apparent Km values of 139 +/– 37 (n = 6), 195 +/- 37 (n = 6), and 113 +/- 16 (n = 6) X 10(-6) M, respectively. Thus, Vmax for S2 greater than S3 congruent to S1, whereas apparent Km was not consistently different among the segments. On the basis of these results we suggest that axial heterogeneity of PAH secretion may reflect an increased basolateral membrane density of PAH transporters of common affinity in the S2 segment of the proximal tubule.
Tubular transport and urinary excretion of phosphate after renal denervation in the anesthetized rat
Authors: Szenasi G. , Bencsath P. , Lehoczky E. , Takacs L.
Published: December 2017

Tubular transport of phosphate (Pi) was studied using clearance and tracer microinjection techniques in Inactin-anesthetized male rats subjected to left kidney denervation. Experiments were conducted in the following groups: i) acute denervation (AD); ii) chronic denervation (CD); iii) acute denervation plus thyroparathyroidectomy (AD + TPTX); iv) microinjection with AD. Besides a marked diuresis and natriuresis with no difference in GFR between innervated (inn) and denervated (den) kidneys, unilateral renal denervation resulted in an increased urinary excretion and decreased tubular reabsorption of inorganic phosphate. Maximum tubular reabsorption of Pi (TmPi) calculated per unit GFR was (means +/- SE): AD, inn: 2.38 +/- 0.04, den: 1.98 +/- 0.06 mumol/ml; CD, inn: 2.66 +/- 0.10, den: 2.19 +/- 0.11 mumol/ml; AD + TPTX, inn: 4.78 +/- 0.06, den: 4.26 +/- 0.08 mumol/ml. Thus, differences in TmPi between the two sides were of the same magnitude in the three groups. Fractional recovery of 32Pi from microinjections in control (C) and postdenervation (D) periods was: early proximal, C: 53.0 +/- 0.81, D: 61.3 +/- 1.07%; late proximal, C: 77.0 +/- 0.81, D: 70.6 +/- 0.60%; early distal, C: 93.7 +/- 0.75, D: 03.5 +/- 0.72%. It is concluded that renal sympathectomy depresses tubular transport of inorganic phosphate in anesthetized rats by a primary action on the proximal convoluted tubule and with a partial compensation in the loop of Henle.
Vasopressin-elicited refractoriness of the response to vasopressin in toad urinary bladder
Authors: Handler J. S. , Preston A. S.
Published: December 2017

Incubation of the urinary bladder of Bufo marinus with high concentrations of vasopressin produces refractoriness to subsequent stimulation of water permeability by low concentrations of vasopressin. Development of refractoriness is directly dependent on concentration of vasopressin and duration of incubation with the hormone. Refractoriness develops in the absence of transepithelial water flow, is evident following a 2-h recovery period of incubation in hormone-free Ringer solution, and is reversed after prolonged incubation in hormone-free Ringer solution. Development and reversal of refractoriness is not altered by actinomycin D or cycloheximide. The steps at which refractoriness develops have been identified partially. Under different conditions, refractoriness involves: 1) reduced vasopressin-sensitive adenylate cyclase activity, 2) reduced epithelial cell cAMP accumulation in response to vasopressin the absence of demonstrable change in vasopressin-sensitive adenylate cyclase activity, cAMP phosphodiesterase activity, or loss of cAMP into the Ringer solution, and 3) refractoriness of water permeability response to exogenous cAMP.
Sodium-calcium interactions in the renal proximal convoluted tubule of the rabbit
Authors: Friedman P. A. , Figueiredo J. F. , Maack T. , Windhager E. E.
Published: December 2017

The effect of experimental maneuvers believed to raise cytosolic [Ca2+] on Na and fluid absorption by isolated perfused proximal convoluted tubules of rabbit kidneys was examined. For this purpose experiments were carried out in which either 1) peritubular [Na] was lowered from 145 mM in controls to 40 mM in experimental periods by isosmotic replacement with Li, tetraethylammonium, or choline; or 2) quinidine (10(-4) M) or A 23187 (5 X 10(-6) M) was added to the peritubular bath containing 145 mM Na. Fluid absorption (Jv), transepithelial unidirectional Na efflux (JNa 1 leads to b), and Na influx (JNa b leads to 1) were measured. Lowering peritubular [Na] inhibited JNa 1 leads to b by 28% and Jv by 61% of the control values. The degree of inhibition of Jv by low peritubular [Na] was dependent on the concentration of ultrafilterable calcium ([Ca]UF) over the range of 0.2-1.0 mM: as perfusate and bath ultrafilterable calcium was reduced, there was an attenuation of the low [Na]-induced inhibition of Jv. Above 1.0 mM [Ca]UF no further increase in inhibition of Jv was observed. Quinidine in the bath inhibited Jv by 37% and JNa 1 leads to b by 28%; A 23187 reduced Jv by 37% and JNa 1 leads to b by 15%. These results are consistent with the view that cytosolic [Ca2+], in turn dependent on a Na-Ca exchange mechanism located at the basolateral cell membrane, regulates, in part, the rate of proximal tubular efflux of sodium, calcium, and water.
Nephrotoxic acute renal failure due to common drugs
Authors: Porter G. A. , Bennett W. M.
Published: December 2017

Antibiotics are the most common drugs implicated in clinical reports of drug-induced nephrotoxicity. The experimental basis for proposed mechanisms of acute renal failure in association with three groups of antibiotics--aminoglycoside, cephalosporin, and amphotericin B--are reviewed in detail. Proposed mechanisms of antibiotic-induced acute renal tubular necrosis involve either altering plasma membrane permeability or interference with cellular energy derived from mitochondria, For either aminoglycoside or cephalosporin antibiotics, cellular accumulation followed by interruption of mitochondrial respiration is the concept that has greatest support, although the possibility of an induced phospholipidosis involving intracellular lysosomes cannot be excluded. Altered renal tubular cell permeability due to the incorporation of amphotericin B into the pore structure of the plasma membrane is consistent with in vivo observation in either clinical or experimental examples of nephrotoxicity with this agent. The metal cis-platinum, used in treatment of neoplastic disease, has a clearly defined incidence of clinical nephrotoxicity with little insight as to cellular mechanisms. A possible mediation involving cis-platinum reducing the protein-bound sulfhydryl group of renal tissue has been proposed. With the ever increasing potency of modern pharmacologic agents come a rising risk of serious toxic side effects.
Sulfate transport in rabbit proximal convoluted tubules: presence of anion exchange
Authors: Brazy P. C. , Dennis V. W.
Published: December 2017

These studies describe the characteristics of sulfate transport in proximal convoluted tubules from rabbit kidney. We measured absorptive and secretory fluxes of sulfate in isolated tubular segments perfused and bathed with fluids containing sulfate concentrations of 0.2–10 mM. At 2.0 mM, the sulfate flux in the absorptive direction averaged 4.76 +/- 0.50 and the secretory flux was 3.08 +/- 0.31 pmol . mm-1 . min-1. Ouabain 10(-5) M decreased each to approx. 1.15 pmol . mm-1 . min-1. Kinetic analysis of each unidirectional sulfate flux demonstrated saturation with increasing sulfate concentrations. Thiosulfate 2 mM in the bath inhibited both absorptive and secretory sulfate fluxes; thiosulfate in the perfusate inhibited only the absorptive flux. Similar results were obtained with 10(-6) M SITS in either bath or perfusate. Phosphate had no effect on sulfate transport. Each unidirectional sulfate flux was influenced by the sulfate concentration in the solution on the opposite side in a pattern consistent with the presence of an anion exchange mechanism. Anion exchange transport persisted at 22 degrees C when net sulfate transport was abolished. The data indicate that sulfate transport in the proximal convoluted tubule is bidirectional, independent of phosphate transport, and occurs via two forms of facilitated transport, one of which is an anion exchange mechanism.
Receptors and effectors in hormone action on the kidney
Authors: Edelman I. S.
Published: December 2017

An analysis is presented of the similarities and differences in receptor-effector relationships in the actions of aldosterone and triiodothyronine on the kidney. Both agents augment tubular reabsorption of sodium at different sites in the nephron. Aldosterone acts primarily distally and triiodothyronine, primarily proximally. In both cases, the respective hormone-receptor complexes associate with target cell chromatin and modulate the abundance of specific coding by mRNAs for regulatory proteins. The quantitative relationships between nuclear-receptor occupancy and responses were analyzed by fractional plots in a bounded domain. When applied to the toad bladder, this analysis revealed a parabolic dependence of the increase in transepithelial Na+ transport on the abundance of nuclear of the increase in transepithelial Na+ transport on the abundance of nuclear aldosterone-receptor complexes. In contrast, four independent response parameters (QO2, QO2(t), Na-K-ATPase, alpha-glycerophosphate dehydrogenase) exhibited a hyperbolic dependence on nuclear abundance of T3 in the rat kidney. The observed cosaturation of nuclear occupancy and responses in both systems, for both hormones, implies that the respective high-affinity binding sites are authentic receptors. Further information is needed on the molecular bases of the nonlinear response-occupancy relationships in hormone action on the kidney.
Na+-dependent H+ efflux from proximal tubule: evidence for reversible Na+-H+ exchange
Authors: Schwartz G. J.
Published: December 2017

Removal of Na+ or addition of ouabain inhibits HCO3(-) and Na+ absorption in rabbit proximal tubule, a finding suggestive of Na+-H+ coupling. However, inhibition of Na+ transport might decrease H+ secretion by reducing energy metabolism rather than by inhibiting Na+-H+ exchange directly. H+ disappearance from the luminal fluid, which depends on direction and magnitude of Na+ gradient, should be a function of cell Na+, independent of cellular metabolism. If cell Na+ is increased by ouabain, H+ disappearance should increase; when cell Na+ is reduced by Na+ removal, less H+ should level the lumen for a given pH difference. Superficial early proximal convoluted tubules were dissected from rabbit kidney and perfused rapidly in vitro with CO2(-) and HCO3(-)-free solutions (pH 6.45). The bath resembled perfusate except that the pH was 7.4 and contained 6 g/dl of albumin. H+ efflux was calculated from the difference in pH between perfused and collected fluid, flow rate, and buffer capacity of the perfusate. When 145 mM Na+ was present in perfusate and bath, H+ efflux was 5.3 +/- 0.4 pmol . cm-1 . s-1 and increased by 39 +/- 16% when ouabain was added to the bath. Replacement of Na+ by choline or Li+ caused a 44 +/- 7% decrease in H+ efflux. Removal of luminal organic solutes markedly reduced H+ efflux; however, it was still enhanced by addition of ouabain to the bath. Even in the absence of Na+ or luminal organic solutes, a substantial apparent H+ leak permeability exists. Addition of 10(-4) M amiloride to a 10 mM Na+ medium caused a 34 +/- 6% reduction in H+ efflux. The results indicate that H+ transport in the proximal tubule is mediated, at least in part, by a reversible Na+-H+ exchanger driven by the difference between H+ and Na+ gradients.
Nature of urate transport in isolated rabbit proximal tubules
Authors: Shimomura A. , Chonko A. , Tanner R. , Edwards R. , Grantham J.
Published: December 2017

Unidirectional fluxes of [14C]-urate from bath to lumen and from lumen to bath were measured in isolated perfused rabbit proximal tubules. The absorption of urate from the perfusate was small in magnitude and relatively insensitive to alteration by luminal probenecid or D-glucose. By contrast, peritubular probenecid inhibited urate secretion from bath to lumen in all three segments. To estimate the facilitated component of urate secretion for each bath concentration of the anion, the passive component of urate influx (probenecid-resistant influx) was subtracted from the total influx of urate. Urate secretion was strongly dependent on concentration of urate in the bath, the relationship being sigmoidal in many S1 and S2 segments. The S0.5 values of 187,251, and 234 X 10(-6) M obtained from Hill plots of mean data from S1, S2, S3 segments, respectively, indicated that the secretory mechanism had a relatively uniform affinity for urate along the proximal tubule. Vmax values for urate secretion were 568,592, and 55 X 10(-15) mol . min-1 . mm-1 for the same segments. Kinetic analysis indicated that axial heterogeneity of urate secretion is probably due to differences in the relative densities of urate transporters of common affinity along the proximal tubule. We suggest that in intact rabbits with low plasma levels urinary urate is the product of glomerular filtration, passive reabsorption, and minimal proximal secretion. With elevation of plasma urate above endogenous levels, S1 and S2 segments secrete urate at an accelerated rate, possibly reflecting action of a transporter with allosteric features.
Collection and analysis of absorbate from proximal straight tubules
Authors: Barfuss D. W. , Schafer J. A.
Published: December 2017

When isolated segments of rabbit proximal straight tubules were perfused under oil at 37 degrees C, we observed that droplets of absorbate formed on the peritubular surface. Volume absorption under these conditions was the same as with customary aqueous bathing solutions when calculated either from the rate of absorbate formation (0.39 +/- 0.03 nl X min-1 X mm-1) or from the difference in measured perfusion and collection rates (0.37 +/- 0.04 nl X min-1 X mm-1). Absorbate formation continued at a steady rate for at least 2 h but was inhibited by 71% at 28 degrees C. The absorbate was found to have a composition that differed from the perfusate, as would be expected in the presence of preferential absorption of glucose, amino acids, and HCO-3. The Cl- concentration in the absorbate was 11.2 +/- 1.8 mM less than in the perfusate. The glucose concentration in the absorbate was 4.5 mM compared with 0.9 mM in the perfusate. Finally, the nonmetabolizable amino acid cycloleucine, which was added to the perfusate at 0.35 mM, had a concentration of 2.9 mM in the epithelial cells compared with 1.6 mM in the absorbate. These data establish the usefulness of this technique for examining solute and water absorption in the proximal nephron and show that the absorbate can differ considerably in solute composition from the luminal perfusate.
A new method for kidney perfusion in situ: application to dynamics of autoregulation
Authors: Simchon S. , Chien S.
Published: December 2017

A procedure for in situ perfusion of kidney was developed in which renal resistance does not rise with continued perfusion at a constant rate and renal blood flow (RBF) can be changed as a step function. The kidney of dogs anesthetized with pentobarbital-chloralose was perfused by a pulsatile syringe pump via an extracorporeal circuit placed between the femoral artery and the renal artery. The perfusion pressure and pulse rate can be adjusted to match those of the dog. Following a step change in RBF from the control level, the dynamics of the autoregulatory response was studied by determining the time course of the alteration in renal perfusion pressure as RBF was maintained at the new constant level. An increase in RBF led to a time-dependent renal vasoconstriction (increase in renal resistance), and a decrease in RBF caused a time-dependent renal vasodilation (decrease in renal resistance). The time course of the response of renal resistance to step changes in RBF can be described by monoexponential functions. The time constant obtained for resistance changes after both an increase and a decrease in RBF was 37.5 +/- 2.8 (SD) s. During the period of step recovery from changes in RBF in either direction, the time constant of the renal resistance response was 53.4 +/- 3.2 s. These values are useful for the analysis of the mechanism of renal autoregulation as well as the modeling of circulatory and hormonal control. The results also indicate that this new procedure for renal perfusion in situ is well suited for studying renal hemodynamics and other functions.
Renal and tubuloglomerular feedback effects of [Sar1,Ala8]angiotensin II in the rat
Authors: Ploth D. W. , Roy R. N.
Published: December 2017

Experiments were done in normal rats to assess kidney, single nephron, and tubuloglomerular feedback responses during control conditions and during renin-angiotensin blockade with the angiotensin II (ANG II) antagonist [Sar1,Ala8]angiotensin II (saralasin, 20 micrograms.kg-1.min-1). Plasma renin activity was increased fourfold during saralasin infusion. Glomerular filtration rate (GFR) and renal blood flow increased in parallel from 1.09 +/- 0.04 to 1.26 +/- 0.05 ml/min and from 6.4 +/- 0.5 to 7.6 +/- 0.5 ml/min, respectively. Absolute and fractional sodium excretion were increased sixfold during ANG II blockade. Hydrostatic pressures in proximal tubules, peritubular capillaries, and distal tubules were unchanged. Estimates of nephron GFR (SNGFR) based on collections of distal tubular fluid were increased from 21.6 +/- 1.2 to 24.3 +/- 0.9 nl/min during ANG II blockade. Increases in SNGFR and decreases in fractional absorption at micropuncture sites beyond the late proximal tubule during saralasin administration resulted in increases of flow rate and Cl- delivery at the early distal tubule. Tubuloglomerular feedback activity, assessed by measuring changes in proximal tubule stop-flow pressure in response to alterations in orthograde microperfusion rate from late proximal tubule sites, was significantly attenuated over the range of physiological flow rates for the late proximal tubule during blockade of the renin-angiotensin system. Acute blockade of ANG II in this rat model results in attenuated tubuloglomerular feedback activity and associated changes of hemodynamic and excretory behavior by the kidney.
Urate uptake in membrane vesicles of rat renal cortex: effect of copper
Authors: Abramson R. G. , King V. F. , Reif M. C. , Leal-Pinto E. , Baruch S. B.
Published: December 2017

[2-14C]Urate uptake was studied in brush border and basolateral membrane vesicles of rat renal cortex. In the absence of copper, urate equilibrated without metabolism of transported urate. Exposure of the vesicles to copper significantly stimulated uptake, and in these vesicles uptake was also stimulated by NaCl or KCl gradients. Allantoin accumulated in these vesicles due to oxidation of transported urate. This oxidation is ascribed to a copper-stimulated, membrane-associated uricase since purified uricase and the membranes had similar Km values, both were inhibited by oxonic acid, and extramembranal uricase was not detected. Oxonic acid and pyrazinoic acid inhibited both uptake and enzyme activity. These findings suggest that urate uptake is carrier mediated and that uricase may play some role in transport. In addition, it appears that a significant loss of copper occurs during isolation of membrane vesicles that profoundly affects the characteristics of urate uptake. Those properties of the membrane that influence urate uptake, however, can be restored by exposure of the membranes to copper.
Effects of long-term infusion of physiologic doses of 1-34 PTH on bone
Authors: Malluche H. H. , Sherman D. , Meyer W. , Ritz E. , Norman A. W. , Massry S. G.
Published: December 2017

It has been suggested that small doses of PTH could exert an anabolic effect on bone and could be beneficial in the management of bone diseases secondary to low bone formation. The effects of 20 wk of continuous infusion of 0.05 U.kg-1.h-1 of 1-34 PTH on cellular, structural, and dynamic parameters of bone were studied in inbred beagles. This physiologic or near physiologic dose of PTH caused a small but significant rise in the concentration of serum calcium and a significant increment in the plasma concentration of 1,25(OH)2D. In addition, the sustained infusion of PTH was associated with a significant increment in volume and surface density of osteoid without a change in bone mass. Mineralization of osteoid was not altered, as evidenced by normal double tetracycline uptake and normal osteoid seam thickness. The enhanced osteoid production was not due to augmented bone formation by individual osteoblasts or basic remodeling units but rather to increased activation frequency resulting in an increased number of remodeling units. There was also augmented bone resorption at the tissue level. The data indicate that small doses of PTH do not have an anabolic effect on the skeleton because they are not associated with increased net bone formation. Rather, PTH administration is associated with an increase in coupled bone turnover.
Marshall Barber and the origins of micropipette methods
Authors: Terreros D. A. , Grantham J. J.
Published: December 2017

Current methods for the study of renal physiology depend heavily on the use of micropipettes fashioned from glass capillary tubes. The technique for making glass micropipettes and manipulating them in the field of a compound microscope appears to have been invented about 1904 by Marshall A. Barber, a bacteriologist at the University of Kansas. Barber's methods were passed on and successively modified by G. L. Kite and R. Chambers, and were finally adapted for renal studies by A. N. Richards. The apparatus for perfusing isolated segments of renal tubules in vitro is remarkably similar to the original device used by Barber over three-quarters of a century ago.
Renal tubular transport of folic acid and methotrexate in the monkey
Authors: Williams W. M. , Huang K. C.
Published: December 2017

The renal excretion of folic acid and methotrexate (MTX) was investigated in pentobarbital-anesthetized cynomolgus, rhesus, and AFrican green monkeys by standard clearance and stop-flow techniques. The renal clearance of folic acid was below inulin clearance at all plasma concentrations studied; the (U/P)folic/(U/P)In ratio increased from 0.26 at a concentration of 0.03 mM to a plateau value of 0.9 at concentrations above 0.2 mM, indicating net reabsorption by a saturable system. In stop-flow experiments, base-line (U/P)folic/(U/P)In ratios during free-flow periods were below 1.0, but increased by twofold in stop-flow samples derived from the proximal tubule, indicating net secretion during stopped flow. The stop-flow pattern of MTX excretion was similar, except the base-line flow pattern of MTX excretion was similar, except the base-line (U/P)MTX/(U/P)In ratio exceeded 1.0, indicating net secretion during both free-flow and stopped-flow periods. Secretion of both compounds was inhibited by p-aminohippuric acid and other organic acids but not by L-glutamic acid. It is concluded that folic acid is transported bidirectionally, while evidence was obtained only for secretion of MTX.
Nonoxidative glucose metabolism a prerequisite for formation of dilute urine
Authors: Baines A. D. , Ross B. D.
Published: December 2017

To examine links between norepinephrine- (NE) stimulated sodium transport and gluconeogenesis, we perfused isolated rat kidneys with 6% albumin, containing various combinations of glucose, alanine, pyruvate. and lactate and inhibitors of gluconeogenesis (0.1 mM mercaptopicolinate, MP) or glucose metabolism (0.2-0.5 mM 2-deoxyglucose, DG). Inulin clearance, fractional potassium reabsorption, total sodium reabsorption, and free water clearance were higher in kidneys perfused with 5 mM glucose plus 2 mM alanine than in kidneys perfused with either 10 mM lactate or 5 mM pyruvate. NE, added after 40 min of perfusion, decreased fractional sodium and potassium excretion in all experiments. In lactate- and/or pyruvate-perfused kidneys NE decreased fractional water excretion with little increase in free water clearance; free water formation was lowest in kidneys perfused with DG or MP. Glucose (5 mM) reversed the inhibitory effect of MP on free water clearance. In glucose-perfused kidneys NE did not decrease fractional water excretion, whereas free water clearance increased threefold. NE stimulated glucose production from pyruvate 2.4-fold and from lactate 1.6-fold. MP inhibited gluconeogenesis both in the basal state and after NE. We conclude that the formation of dilute urine requires nonoxidative glucose metabolism to maintain low water permeability in the diluting segment and a high peritubular glucose concentration that is ensured by gluconeogenesis in adjacent proximal tubules.
Proximal reabsorption during metabolic acidosis in the rat
Authors: Cogan M. G. , Rector F. C.
Published: December 2017

The mechanism by which proximal volume reabsorption is reduced during hyperchloremic metabolic acidosis was studied using free-flow micropuncture techniques in Munich-Wistar rats. Compared with control hydropenic conditions, absolute rates of proximal total CO2 and water reabsorption rates during NH4Cl-induced metabolic acidosis were diminished: from 557 +/- 35 to 204 +/- 19 pmol/min and from 13.0 +/- 1.0 to 9.7 +/- 0.6 nl/min, respectively. Inhibition of proximal volume reabsorption during metabolic acidosis was not attributable to alterations in the reabsorptive Starling forces, since peritubular capillary oncotic and hydraulic pressures were normal, or to acidemia itself, since acute respiratory acidosis was not found to decrease reabsorption. When partial repair of the acidosis was achieved by NaHCO3 infusion, absolute reabsorption of both total CO2 (390 +/- 48 pmol/min) and water (12.2 +/- 1.1 nl/min) significantly increased despite modest extracellular volume expansion. NaCl infusion in acidotic animals had no restorative effect on volume reabsorption. Mean values for single nephron glomerular filtration rate were similar under all conditions. Absolute chloride reabsorption tended to correlate better with absolute bicarbonate reabsorption and, hence, with the magnitude of the chloride concentration gradient developed than with the filtered chloride load. In conclusion, absolute proximal volume reabsorption during metabolic acidosis and its partial repair correlated with the absolute magnitude of bicarbonate filtered and reabsorbed. It is proposed that proximal volume reabsorption may be regulated, at least in part, by the anion composition of the glomerular ultrafiltrate.
Evidence for altered glomerular hemodynamics during acute nephron obstruction
Authors: Ichikawa I.
Published: December 2017

The stop-flow technique has been used to estimate mean glomerular capillary hydraulic pressure (PGC). This technique involves complete obstruction of fluid flow in single proximal tubules, thereby altering the formation of glomerular filtrate as well as the delivery of fluid to more distal segments of the same nephron. To determine whether tubule obstruction affects PGC, pressures were measured in capillaries of accessible glomeruli before and during proximal tubule obstruction in hydropenic Munich-Wistar rats. The results were compared with estimates of PGC obtained for these same glomeruli by the stop-flow technique. When glomerular filtration was unhindered, blockade of fluid flow into the loop of Henle did not alter directly measured PGC values. When glomerular filtration was stopped by proximal tubule obstruction, directly measured PGC values increased by approximately 7 mmHg. Stopping glomerular filtration also increased postglomerular capillary hydraulic pressure, suggesting that acute single nephron obstruction and cessation of filtration substantially affects these pressures by diverting fluid to the postglomerular capillary bed. Indirect stop-flow estimates of PGC did not differ from direct measurements of PGC in the same glomeruli during stopped flow. Thus, in the normal hydropenic condition, stop-flow estimates of PGC accurately measure PGC. However, the PGC value prevailing under the stop-flow condition is substantially elevated over the PGC existing when filtration is proceeding normally.
Systemic effects of NaHCO3 in experimental lactic acidosis in dogs
Authors: Arieff A. I. , Leach W. , Park R. , Lazarowitz V. C.
Published: December 2017

Lactic acidosis is characterized by metabolic acidosis due to accumulation of H+ ions from lactic acid with blood lactate of at least 5 mM. The standard treatment is intravenous NaHCO3, with resultant mortality in excess of 50%. Despite the high mortality, the metabolic and systemic effects of NaHCO3 used in the treatment of lactic acidosis have not been extensively studied. The present experiments in diabetic dogs were designed to address these questions. Dogs with phenformin-induced lactic acidosis (blood lactate above 5 mM, arterial pH below 7.20) were treated with equimolar amounts of either NaCl or NaHCO3 or received no therapy. Intravenous NaHCO3 resulted in a decline of cardiac output and intracellular pH (pHi) of liver and erythrocytes, whereas treatment with NaCl did not. With NaHCO3 but not with NaCl infusion gut lactate production increased almost stoichiometrically, with no change in arterial pH or bicarbonate but with a doubling of lactate. Bicarbonate also resulted in a decrease of hepatic portal vein blood flow. The mean survival time and percent mortality were similar in NaCl- vs. NAHCO3(-) treated animals. Although both groups lived longer than did animals receiving no therapy, the differences were not significant. Thus, treatment of experimental lactic acidosis with either NaCl or NaHCO3 or with no therapy results in no change of blood pH and bicarbonate and in a similar mortality. In terms of systemic effects, however, NaHCO3 results in significant decrements of liver and erythrocyte pHi, hepatic portal vein blood flow, and cardiac output and in significant increments of gut lactate production, whereas NaCl does not. The data suggest that the rationale for therapy of lactic acidosis with NaHCO3 should probably be reevaluated.
2-Deoxy-D-glucose transport in dog kidney
Authors: Silverman M. , Turner R. J.
Published: December 2017

Osmotically active brush border membrane (BBM) and antiluminal membrane (ALM) vesicles prepared from dog kidney cortex were used to investigate transport of 2-deoxy-D-glucose (2DG). A parallel in vivo study was carried out using the pulse-injection multiple indicator-dilution technique. Single-pass indicator-dilution experiments demonstrate both luminal and antiluminal interactions for 2DG. The antiluminal interaction is blocked by large systemic doses of phlorizin (100-200 mg/kg). With plasma glucose concentration in the range of 4-5 mM fractional luminal extraction of 2-[14C]DG relative to simultaneously filtered creatinine is 25 +/- 2%. This luminal extraction can be inhibited by raising plasma glucose concentration to approximately 30 mM and by administration of low systemic doses of phlorizin (6-8 mg/Kg). 2DG uptake into BBM vesicles equilibrates into the same intravesicular volume as D-glucose. A definite Na+ component of 2DG uptake can be defined which is more sensitive to inhibition by phlorizin than by phloretin and is also inhibited by D-glucose and alpha-methyl-D-glucoside but not by L-glucose. But compared with D-glucose, the Na+-dependent BBM uptake of 2DG is greatly reduced. 2DG uptake into ALM vesicles is independent of Na+, is more sensitive to inhibition by phloretin than by phlorizin, and is also blocked by cytochalasin B but not by alpha-methyl-D-glucoside. Influx of 2-[14C] DG into ALM vesicles is increased by preloading with unlabeled D-glucose. Conversely influx of D[14C]glucose into ALM vesicles is accelerated by preloading with unlabeled 2DG. ALM influx of radiolabeled 2DG is accelerated by D-glucose, 3-O-methyl-D-glucose, D-galactose, and unlabeled 2DG but not by alpha-methyl-D-glucoside. The specificity of inhibition and countertransport results from in vivo and in vitro experiments are consistent with the proposal that 2DG shares a common carrier mechanism with D-glucose at each of the opposing membrane surfaces.
Potassium transport by the renal distal tubule: effects of potassium loading
Authors: Stanton B. A. , Giebisch G. H.
Published: December 2017

Microperfusion studies were performed on superficial distal tubules to determine the relationship between potassium secretion by the distal tubule and plasma potassium concentrations in rats on a control and a high potassium diet. Potassium was infused in graded doses into animals on a control diet and into animals receiving a high potassium diet. Since potassium loading in rats is known to inhibit proximal tubular sodium and fluid reabsorption and thereby could lead to nonspecific flow-related stimulation of potassium secretion by the distal tubule, continuous microperfusion techniques at constant flow rate were used to measure the rate of potassium secretion. Additionally, plasma aldosterone levels were measured and renal clearance experiments carried out. The results show that potassium secretion, restricted to cells of the late distal tubule, reaches a maximal rate at a plasma potassium concentration of about 6 meq/liter. Potassium adaptation significantly enhances potassium secretion compared with animals on a control diet over a range of plasma potassium from 3.8 to 7.4 meq/liter. Enhanced potassium secretion by the distal tubule, in both control and potassium-adapted animals, is associated with increased aldosterone levels.
Effect of differing concentrations of parathyroid hormone on rat renal electrolyte excretion
Authors: Carney S. , Thompson L.
Published: December 2017

Urinary clearance studies were performed on acutely thyroparathyroidectomized rats to study the effect of a range of parathyroid hormone (PTH) concentrations on renal electrolyte transport. PTH 0.1 U, prime and per hour, significantly increased the plasma calcium concentration, yet fractional calcium excretion was increased by 47.5% and inorganic phosphate excretion remained unaltered. PTH 1 U produced a similar increase in the plasma calcium concentration. However, urinary calcium excretion was unchanged when compared with control animals and a small phosphaturia occurred (from 0.1 +/- 0.1 to 0.8 +/- 0.2%; P less than 0.05). PTH 10 U decreased fractional calcium excretion by 50% and increased fractional phosphate excretion from 0.4 +/- 02. to 19.4 +/- 1.7% (P less than 0.01). Changes in urinary magnesium excretion were similar to those of calcium, being increased with the lowest PTH concentration yet decreased with a 100-fold increase in PTH concentration. These data suggest that PTH, at a low physiological concentration that acts on bone, does not directly alter renal electrolyte handling. High physiological concentrations of PTH, however, produce a brisk phosphaturia and reduce calcium and magnesium excretion. A reappraisal of the accepted role of PTH on renal calcium conservation is therefore required.
Dysfunction of the proximal tubule underlies maleic acid-induced type II renal tubular acidosis
Authors: Al-Bander H. A. , Weiss R. A. , Humphreys M. H. , Morris R. C.
Published: December 2017

To investigate whether dysfunction of the proximal tubule underlies maleic acid-(MA) induced type II (“proximal”) renal tubular acidosis (RTA II), we intravenously administered either MA or acetazolamide to eight conscious trained dogs undergoing water diuresis and examined the relationship between fractional solute-free water clearance (Ch2o/GFR), a measure of NaCl reabsorption in the post-proximal nephron, and either fractional urine flow (V/GFR), a measure of total solute rejected by the proximal tubule, or the sum of fractional excretion of Cl- and Ch2o/GFR [(Ccl + Ch2o)/GFR], a measure of proximally rejected solute that is potentially reabsorbable by the thick ascending limb. When MA or acetazolamide induced brisk bicarbonaturia at normal plasma bicarbonate concentrations: 1) V/GFR, (Ccl + Ch20)GFR, and Ch2o/GFR increased strikingly; 2) at any increment of Ch2o/GFR ws not; 3) the increments of V/GFR correlated positively with those of fractional excretion of bicarbonate (P less than 0.001); 4) during hyperchloremic acidosis, MA-induced bicarbonaturia was greatly attenuated; the increment in V/GFR was halved and approximated that in Ch20/GFR, which was unchanged; 5) when plasma bicarbonate was abruptly increased, bicarbonaturia increased strikingly and V/GFR increased further but Ch20/GFR and aminoaciduria did not. We conclude that MA induces a reduction in the net rate at which the proximal tubule reabsorbs HCO-3, Na+, and Cl-. This dysfunction underlies RTA II and evokes greatly increased reabsorption of Cl- and Na+ in the post-proximal tubule.
Urate transport via anion exchange in dog renal microvillus membrane vesicles
Authors: Kahn A. M. , Aronson P. S.
Published: December 2017

The transport of urate was evaluated in brush border membrane vesicles isolated from the dog renal cortex. It was previously shown that uphill urate and p-aminohippurate (PAH) uptake into these membrane vesicles results from imposing an outwardly directed OH- gradient. In the present study, the OH- gradient-stimulated uptake of urate was inhibited by external Cl-. In the absence of OH- gradients, imposing an outwardly directed Cl- gradient induced the transient accumulation of urate against its concentration gradient (overshoot), whereas imposing an inwardly directed Cl- gradient induced the transient uphill efflux of urate (undershoot). The effects of Cl- gradients on urate transport persisted when the diffusion potentials caused by the Cl- gradients were negated by superimposing K+ gradients in the presence of the K+ ionophore valinomycin. The dose-response curves for three different inhibitors were identical for the OH- and Cl- gradient-stimulated modes of urate uptake. The uptake of PAH was also stimulated by imposing an outwardly directed Cl- gradient. The dose-response curves for probenecid inhibition were identical for the OH- and Cl- gradient-stimulated modes of PAH uptake. Finally, the existence of a Na+ cotransport pathway for urate or PAH could not be demonstrated. We conclude that the principal mechanism for urate transport in dog renal microvillus membrane vesicles is via an anion exchanger with affinity for urate, PAH, OH-, and Cl-. This anion exchanger may play an important role in mediating organic anion reabsorption and secretion in the proximal tubule.
Nephron site of effect of nonsteroidal anti-inflammatory drugs on solute excretion in humans
Authors: Kaojarern S. , Chennavasin P. , Anderson S. , Brater D. C.
Published: December 2017

Indomethacin and other nonsteroidal anti-inflammatory drugs (NSAIDs) decrease solute excretion when administered acutely to normal subjects. We performed clearance studies during water loading of 10 normal volunteers and during hydropenia in eight additional subjects to determine the nephron site of this effect using indomethacin and carprofen as inhibitors of prostaglandin (PG) synthesis. Their administration decreased fractional excretion of sodium, chloride, and volume. During water loading, fractional clearance of free water decreased from 0.13 +/- 0.04 during the control study to 0.09 +/- 0.03 and 0.06 +/- 0.02 with indomethacin and carprofen, respectively. However, fractional delivery of solute to the dilution segment decreased in parallel such that free water clearance corrected for delivery did not change with either drug. In humans, therefore, the decrement in solute excretion that occurs with administration of NSAIDs occurs prior to the diluting segment. During hydropenia, free water reabsorption relative to osmolar clearance increased (P less than 0.01). In both studies, neither the marker of renal perfusion or of proximal nephron function changed with inhibition of PG synthesis. The data indicate that at the tubular level, NSAIDs increase solute reabsorption at the medullary segment of the thick ascending limb of the loop of Henle. Therefore, a physiologic role of renal prostaglandins at this nephron site is implied.
Na:H exchange and the primary H pump in the proximal tubule
Authors: Bichara M. , Paillard M. , Leviel F. , Prigent A. , Gardin J. P.
Published: December 2017

Cell pH (pHi) transients were monitored at 5-min intervals with the weak acid 5,5-[14C]dimethyloxazolidine-2,4-dione and membrane potentials were estimated from the distribution of [3H]triphenylmethylphosphonium ion in separated proximal tubules (SPT) or rabbit kidney. SPT suspensions were gassed at 37 degrees C first with 5% CO2 and then with 15% CO2. Under normal conditions, pHi rapidly fell during initial 15% CO2 acid loading and then recovered within 20 min. In the presence of 10(-3) M ouabain, which eliminated Na:H exchange as a driving force for H+ secretion, initial cell acidification was still followed by cell pH recovery, which demonstrated a sodium gradient-independent H+ extruding mechanism. In the presence of 10(-3) M ouabain plus 10(-4) M potassium cyanide, there was no pHi recovery following initial cell acidification but, on the contrary, further progressive cell acidification occurred, which is compatible with passive diffusion only of HCO-3 out of the cell. From the cyanide experiments, an apparent permeability coefficient for HCO-3 of the basolateral cell membrane was calculated; this latter result allowed the calculation of rates of passive HCO-3 diffusion and of active H+ extrusion under normal conditions and in the presence of 10(-3) M ouabain. We conclude that in the proximal tubule 1) there is a primary H+ pump additional to Na:H exchange; and 2) this primary H+ pump is responsible for about 25% of active H+ extrusion following acute CO2 cellular acid loading.
Sodium chloride and water transport in the renal distal tubule of the rainbow trout
Authors: Nishimura H. , Imai M. , Ogawa M.
Published: December 2017

Isolated segments of the renal tubules from the freshwater trout, Salmo gairdneri, were perfused in vitro to characterize ion and water transport. The distal tubule showed a transepithelial voltage (Vt) positive in the lumen (+17.8 +/- 1.4 mV). Furosemide added to the lumen and Na cyanide and ouabain added to the bath reduced the lumen-positive Vt of the distal tubule. Removal of either Cl- or Na+ from both perfusate and bathing medium abolished the lumen-positive Vt. When the distal tubule was perfused and bathed with isosmotic solution, net water flux (Jv) was nearly zero. Jv and hydraulic conductivity remained low when the osmolality of the bathing fluid was increased with raffinose. Neurohypophysial hormones added to the bath showed no effect. Chloride efflux (lumen to bath, 171.1 +/- 17.1 peq x mm-1. min-1) was significantly higher than chloride influx (bath to lumen, 105.6 +/- 12.3 peq x mm-1 x min-1), suggesting that net chloride reabsorption exists. These results suggest that in the freshwater trout, which lack the loop of Henle, the distal tubule acts as a diluting segment. The presence of sodium, in addition to chloride, is required to generate the lumen-positive Vt in the distal tubule.