bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of angiotensin II natriuresis and antinatriuresis
Authors: Olsen M. E. , Hall J. E. , Montani J. P. , Guyton A. C. , Langford H. G. , Cornell J. E.
Published: December 2017

The aim of this study was to determine the role of changes in renal arterial pressure (RAP), renal hemodynamics, and tubular reabsorption in mediating the natriuretic and antinatriuretic actions of angiotensin II (ANG II). In seven anesthetized dogs, endogenous ANG II formation was blocked with captopril, and ANG II was infused intravenously at rates of 5-1,215 ng X kg-1 X min-1 while RAP was either servo-controlled at the preinfusion level or permitted to increase. When RAP was servo-controlled, ANG II infusion at all rates from 5-1,215 ng X kg-1 X min-1 decreased urinary sodium excretion (UNaV) and fractional sodium excretion (FENa) while increasing fractional reabsorption of lithium (FRLi) (an index of proximal tubular fractional sodium reabsorption) and causing no change in calculated distal tubule fractional sodium reabsorption (FRDNa). When RAP was permitted to increase, ANG II infusion rates up to 45 ng X kg-1. min-1 also decreased UNaV and FENa while increasing FRLi and causing no change in FRDNa. However, at 135 ng X kg-1 X min-1 and above, UNaV and FENa increased while FRLi and FRDNa decreased when RAP was allowed to rise, even though renal blood flow and filtration fraction were not substantially different from the values observed when RAP was servo-controlled. Filtered sodium load was slightly higher when RAP was permitted to increase during ANG II infusion compared with when RAP was servo-controlled, although the differences were not statistically significant. Thus, even very large doses of ANG II cause antinatriuresis when RAP is prevented from increasing.(ABSTRACT TRUNCATED AT 250 WORDS)
Response of serum 1,25(OH)2D3 to variation of ionized calcium during chronic acidosis
Authors: Bushinsky D. A. , Riera G. S. , Favus M. J. , Coe F. L.
Published: December 2017

Chronic ammonium chloride (NH4Cl) administration causes metabolic acidosis and prevents the normal rise of serum 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] during a low-calcium diet (LCD, 0.002% calcium). The suppression of serum 1,25(OH)2D3 was not due to reduced parathyroid hormone concentration, elevated serum phosphorus, or total calcium concentration. Acidosis increased blood ionized Ca [Ca2+] and proton [H+] concentrations. Serum 1,25(OH)2D3 levels were inversely correlated with both [Ca2+] and [H+]. To determine the independent effects of [Ca2+] on serum 1,25(OH)2D3 we varied [Ca2+] at a constant [H+] by infusing either EGTA or saline for 24 h after 11 days of LCD and NH4Cl. EGTA, preequilibrated with three concentrations of Ca, lowered [Ca2+] and raised 1,25(OH)2D3 but did not alter [H+] or serum phosphorus concentration. The log of serum 1,25(OH)2D3 varied linearly and inversely with arterial blood [Ca2+] during saline (r = -0.884, n = 8, P less than 0.001) and EGTA infusions (r = -0.798, n = 22, P less than 0.001). At all levels of [Ca2+], rats infused with EGTA had a higher serum 1,25(OH)2D3 than those infused with saline. Log serum 1,25(OH)2D3 was correlated neither with [H+] nor pH. Elevated [Ca2+] and not [H+] appears to suppress the serum 1,25(OH)2D3 response to LCD during NH4Cl acidosis in the rat.
Lack of intramembranous particle clusters in collecting ducts of mice with nephrogenic diabetes insipidus
Authors: Brown D. , Shields G. I. , Valtin H. , Morris J. F. , Orci L.
Published: December 2017

We suggested previously, on the basis of indirect evidence, that in two strains of mice with nephrogenic defects of urinary concentration the deficiency arose from an inadequate rise in water permeability of the collecting duct system. In this study we tested the question further by assuming that the frequency of intramembranous particle (IMP) clusters seen by freeze-fracture can be used as a morphological marker of vasopressin-induced water permeability. Three genotypes of mice were studied: 1) DI +/+ Severe, with florid, vasopressin-resistant diabetes insipidus; 2) DI +/+ Nonsevere, with an intermediate deficiency of urinary concentration; and 3) normal, VII +/+ mice. In addition, we examined a group of DI +/+ Severe mice that had been injected with exogenous 1-desamino-8-D-arginine vasopressin (DDAVP) subcutaneously for 3 days. Since the results in this group did not differ from those in untreated DI +/+ Severe mice, all data for this genotype were combined. IMP clusters within luminal membranes of inner medullary collecting duct principal cells were quantified by freeze-fracture electron microscopy. Urinary osmolality and percentage of cells showing clusters were, respectively: 203 +/- 43 mosmol/kg H2O and 0% in DI +/+ Severe mice; 1,133 +/- 86 and 33 +/- 4 in DI +/+ Nonsevere mice; and 2,234 +/- 190 and 52 +/- 5 in VII +/+ animals. With the exception of one animal, there was no overlap of the data, which were significantly different from one another for each variable. We conclude that in DI +/+ Severe mice, both endogenous and exogenous vasopressin are unable to increase the water permeability of medullary collecting ducts.(ABSTRACT TRUNCATED AT 250 WORDS)
Dependence of intracellular Na+ concentration on apical and basolateral membrane Na+ influx in frog skin
Authors: Stoddard J. S. , Helman S. I.
Published: December 2017

An isotopic method was developed to measure the intracellular Na+ content of the transepithelial Na+ transport pool of frog skin. Isolated epithelia (no corium) were labeled with 24Na either asymmetrically, from apical (Aa) or basolateral (Ab) solutions, or symmetrically (Aab). Transport pool Na+ could be identified from the kinetics of washout of 24Na carried out in the presence of 1 mM ouabain, 100 microM amiloride, and 1 mM furosemide that served to trap cold Na+ and 24Na within the transport pool. In control epithelia, Aab averaged 64.1 neq/cm2 (13.9 mM), and maximal inhibition of apical membrane Na+ entry with 100 microM amiloride caused Aab to decrease to 24.3 neq/cm2 (5.3 mM). Ouabain caused Aab to increase markedly to 303 neq/cm2 in 30 min, whereas amiloride inhibition of apical membrane Na+ entry reduced markedly the rate of increase of Aab caused by ouabain (7.3 neq X cm-2 X min-1 in control and 1.7 neq X cm-2 X min-1 in the presence of amiloride). These data, in part, confirmed the existence of an important basolateral membrane permeability to Na+ that was measured in separate studies of the bidirectional 24Na fluxes at the basolateral membranes of the cells. Both sets of data were supportive of the idea that a significant Na+ recycling exists at the basolateral membranes of the cells that contributes to the Na+ load on the pump and Na+ recycling participates in the regulation of the Na+ concentration of the Na+ transport pool of these epithelial cells.
Role of inner medullary collecting duct NaCl transport in urinary concentration
Authors: Chandhoke P. S. , Saidel G. M. , Knepper M. A.
Published: December 2017

Mathematical modeling and simulation techniques were used to analyze the role of medullary collecting duct NaCl transport in the urinary concentrating process. The mathematical model incorporated experimentally determined epithelial transport parameters and anatomical parameters obtained chiefly from experiments in rabbit kidneys. The simulations predict that solute concentration profiles along the medullary collecting ducts are highly sensitive to the rate and pattern of active NaCl absorption along the length of the collecting duct system. When active NaCl absorption was assumed to be zero in the outer medullary collecting duct and to increase along the inner medulla to a very high value at the papillary tip, the simulated solute concentration profiles in the medullary collecting ducts as well as relative concentrations between different inner medullary structures agreed well with experimental data. However, despite optimal choice of collecting duct transport parameters and the use of experimentally determined permeability coefficients, only modest total solute gradients could be generated axially in the inner medullary interstitium, and passive luminal dilution did not occur in the thin ascending limb. We conclude: 1) Axial heterogeneity of transport properties along the inner medullary collecting duct must be assumed to explain in vivo findings from micropuncture and microcatheterization studies. 2) Active NaCl transport from the inner medullary collecting ducts is important chiefly for efficient conservation of NaCl rather than for concentration of solutes in the renal inner medulla. 3) Important inconsistencies exist between several previously reported experimental observations and the theoretical requirements for passive luminal dilution in the thin ascending limb of Henle's loop.
Glomerular blood flow after single nephron obstruction in the rat kidney
Authors: Tanner G. A. , Knopp L. C.
Published: December 2017

This study examined the effects of kidney tubule lumen obstruction on glomerular blood flow (GBF) in anesthetized rats. GBF was estimated using microspheres having 9 micron diameter and averaged 239 +/- 10 nl/min in normal nephrons of 41 control rats. Tubule blockade with either paraffin wax or castor oil produced identical results. GBF after 1-2 h of obstruction did not differ from normal. After 1 day, GBF averaged two-thirds of normal, and after 1 wk GBF averaged one-third of normal. The hemodynamic changes produced by obstruction for 1 wk were diminished by chronic administration of high doses of the converting enzyme inhibitor captopril or acute administration of the angiotensin antagonist saralasin. The results suggest that angiotensin contributes to the vasoconstriction produced by prolonged obstruction. Nephrons blocked with castor oil contained oil 1 wk later, had a GBF of 88 +/- 24 nl/min, and were atrophied. We conclude that chronic single nephron obstruction produces progressive vasoconstriction, that this response is in part angiotensin mediated, and that the end result is nephron atrophy.
Parathyroid hormone inhibits water flow in the isolated toad bladder
Authors: Sabatini S.
Published: December 2017

These experiments studied the effect of parathyroid hormone (PTH) (1-84) on water and Ca transport in isolated toad bladder sacs and toad bladder epithelial cells. Serosal addition of PTH significantly inhibited maximal water flow induced by vasopressin or exogenous cyclic AMP. This effect was seen over a wide range of concentrations, with the threshold for the effect occurring at 1 ng/ml. Pretreatment of the toad bladder sacs with prostaglandin inhibitors (indomethacin or ibuprofen, 1 X 10(-6) M) or preincubation in low-Ca medium (0.089 mM) abolished the effect of PTH on vasopressin-stimulated water flow. Pretreatment of the toad bladders with lanthanum (5 X 10(-5) M) also abolished the effect of PTH on vasopressin-stimulated water flow. Synthetic PTH (1-34) inhibited vasopressin-stimulated water flow only at a high concentration (1 microgram/ml). PTH increased 45Ca uptake by toad bladder epithelial cells but had no effect on 45Ca efflux. These results demonstrate that PTH inhibits water transport beyond the generation of cyclic AMP. That the effect of PTH was abolished in a low-Ca medium or by pretreatment with lanthanum suggests that cell Ca uptake is required for the effect of PTH on water transport. That prostaglandin inhibitors also block the effect of PTH on vasopressin-stimulated water flow suggests that prostaglandin synthesis is required for the effect. These data suggest that the effect of PTH on water flow is mediated by an increased cellular uptake of Ca that stimulates prostaglandin release. Prostaglandin release, in turn, appears to mediate the inhibitory effect of PTH on vasopressin-stimulated water transport.(ABSTRACT TRUNCATED AT 250 WORDS)
Aspects of electrolyte transport across isolated dog retinal pigment epithelium
Authors: Tsuboi S. , Manabe R. , Iizuka S.
Published: December 2017

Transport of Na and Cl across the isolated dog retinal pigment epithelium (RPE) choroid was investigated. Under the short-circuit condition, a net Na flux was observed from choroid to retina and a net Cl flux was determined in the opposite direction. The current created by the net flux of these two ions was larger than the short-circuit current (SCC). Addition of 10(-5) M ouabain to the apical side inhibited net fluxes of both Na and Cl, whereas it reduced the SCC 84%. Addition of 10(-4) M furosemide to the apical side inhibited net Cl flux but had no effect on the net Na transport. The 10(-4) M furosemide reduced the SCC 38%. These drugs had no effect when applied to the basal side. Thus the transport of both Na and Cl depends on the Na-K-ATPase in the apical membrane of the dog RPE. A furosemide-sensitive neutral carrier at the apical membrane is suggested for the transport of Cl. Replacement of HCO3 with SO4 in the bathing solution caused an increase in the SCC, indicating the choroid-to-retina movement of HCO3 across the short-circuited dog RPE choroid.
Characteristics of the proton pump in rat renal cortical endocytotic vesicles
Authors: Sabolic I. , Burckhardt G.
Published: December 2017

The characteristics of the H+ pump in isolated rat renal endocytotic vesicles were studied by the delta pH-sensitive dye acridine orange, the voltage-sensitive dye 3,3'-dipropylthiadicarbocyanine iodide, and by a coupled optical ATPase assay. Intravesicular acidification depended on ATP and Mg2+ concentrations with half-maximal activations at 73 and 77 microM, respectively. CTP, GTP, UTP, and ITP partially supported acidification, but ADP and AMP did not. Ouabain, ethoxzolamide, levamisole, and vanadate did not inhibit H+ uptake into endocytotic vesicles. Oligomycin inhibited partially. Depending on concentration and preincubation time, Dio-9, filipin, N-ethylmaleimide (NEM), and dicyclohexylcarbodiimide (DCCD) inhibited H+ uptake completely. Filipin and, partially, DCCD acted nonspecifically by dissipating pH gradients. A specific cation was not required for the H+ pump; Zn2+ inhibited. Compared with mannitol, ATP-driven H+ uptake was stimulated by SCN- greater than Cl- greater than Br- greater than I- much greater than HPO4(2-) = gluconate = HCO3- = F-, but not by SO4(2-), NO3-, CH3COO-, S2O3(2-), and S4O6(2-). Chloride stimulated H+ uptake from the outside of the vesicles with an apparent Km of 27 mM. In the absence of Cl-, ATP-driven proton uptake was increased by intravesicular K+ and valinomycin, suggesting that the pump is electrogenic. The electrogenicity, however, could not be demonstrated with voltage-sensitive dyes. The vesicle membrane contains no significant K+ and Cl- conductances; only a conductance for H+ was found. The vesicles exhibited an ouabain-, oligomycin-, and vanadate-insensitive ATPase activity that was inhibited by DCCD and NEM. Our data indicate the presence of an electrogenic H+ pump in endocytotic vesicles from rat renal proximal tubules with similar characteristics as H+ pumps present in various intracellular (nonmitochondrial) membranes.
Chloride transport by rat renal proximal tubule: effects of bicarbonate absorption
Authors: Bomsztyk K.
Published: December 2017

In the early part of the proximal tubule chloride concentration is increased above that in plasma, a change attributed to preferential absorption of bicarbonate with sodium and water. To determine the mechanism(s) of the preferential absorption of HCO3 over chloride, in vivo paired perfusions were done in surface proximal tubules of the rat kidney. Each tubule was perfused with a control bicarbonate solution, similar in ionic composition to the solution normally present in the early part of the proximal tubule, and one of the experimental solutions that were modified by either replacing all of bicarbonate with sulfate, N-2-hydroxyethylpiperazine-N'-ethanesulfonate (HEPES), or all bicarbonate with sulfate and sodium with lithium, or addition of acetazolamide (ATZ), or cyanide (CN). Sufficient mannitol was added to reduce net fluid flux to zero. When sulfate replaced bicarbonate in luminal fluid, net chloride absorption was enhanced, a change associated with low lumen HCO3 and low pH. ATZ inhibited HCO3 absorption, whereas net Cl absorption increased, an effect associated with high HCO3 and low pH. With HEPES-plus-ATZ solutions, chloride absorption also increased but, in contrast to SO4 or ATZ solutions, pH increased. With sulfate and lithium replacement chloride absorption also increased despite net sodium secretion. CN, a metabolic inhibitor, inhibited HCO3 and sodium absorption but stimulated net chloride absorption. The data indicate that HCO3 absorption inhibits chloride absorption, a process independent of luminal HCO3 per se, luminal pH, sodium absorption, and transepithelial volume flux and voltage.
Enhanced renal tubular ouabain-sensitive ATPase in streptozotocin diabetes mellitus
Authors: Wald H. , Scherzer P. , Popovtzer M. M.
Published: December 2017

The effect of streptozotocin-induced diabetes mellitus on rat renal ouabain-sensitive ATPase in six distinct nephron segments was studied. Twenty-four hours after administration of streptozotocin, blood glucose increased threefold (P less than 0.001), and glucosuria was evident. Aldosterone levels increased almost twofold (P less than 0.001). Ouabain-sensitive ATPase increased in the proximal segments PC (proximal convoluted tubule) and PS (proximal straight tubule) by 43 and 62%, respectively, (P less than 0.001) and CD (cortical collecting duct) ouabain-sensitive ATPase increased 77% (P less than 0.001). Ouabain-sensitive ATPase in the cortical (CTAL) and medullary (MTAL) thick ascending limbs of Henle's loop and in the DC (distal convoluted tubule) remained unchanged after 24 h of streptozotocin administration. Eight days after streptozotocin administration, when glomerular filtration rate (GFR) was already markedly elevated, ouabain-sensitive ATPase remained increased in the PC, PS, and CD but was significantly less compared with the activity after 24 h (P less than 0.05), whereas in the CTAL and MTAL a marked increase in ouabain-sensitive ATPase occurred by 54% in the CTAL and 65% in the MTAL (P less than 0.001). Aldosterone levels remained elevated compared with control but less than after 24 h. Pretreatment with deoxycorticosterone acetate abolished the increase in ouabain-sensitive ATPase in the CD. These findings show that streptozotocin-induced diabetes mellitus in the rat is associated with a substantial increase in ouabain-sensitive ATPase activity along most of the nephron. This increase in enzyme activity may represent a mechanism of physiological adaptation of the nephron to maintain electrolyte homeostasis in diabetes in face of the increased GFR and osmotic diuresis.
Determination of prostaglandin E2 synthesis along rabbit nephron by enzyme immunoassay
Authors: Farman N. , Pradelles P. , Bonvalet J. P.
Published: December 2017

Prostaglandin E2 (PGE2) content and synthesis have been measured in microdissected segments from the entire nephron of rabbit kidney. PGE2 was determined by an enzyme immunoassay on glomeruli or tubular segments (0.5-5 mm) either immediately after microdissection (PGE2 content) or after incubation for 15 min at 37 degrees C in the presence of arachidonic acid (PGE2 synthesis). We confirmed that collagenase used for microdissection did not modify PGE2 synthesis. A linear correlation was found between the length of tubule used in the assay and PGE2 synthesis, as well as between incubation time with arachidonic acid and PGE2 synthesis. PGE2 synthesis, expressed in picograms per millimeter tubular length per 15 min, was maximum in medullary collecting duct (517 +/- 73). High values were also found in the granular portion of distal tubule (134 +/- 22) and granular or light portion of cortical collecting tubule (199 +/- 24 and 146 +/- 10, respectively). Synthesis was lower in all other segments: 17 +/- 6 and 24 +/- 12, respectively, in convoluted and straight proximal tubule, 67 +/- 12 and 71 +/- 5, respectively, in thin descending and ascending limb, 51 +/- 9 and 23 +/- 4, respectively, in medullary and cortical thick ascending limb of Henle's loop, and 25 +/- 7 in initial distal tubule. Synthesis per glomerulus was 24 +/- 3. When the protein content of each nephron segment is taken into account, this profile was not modified, except for the thin limbs of the loop, which reached values per nanogram protein slightly higher than those of the cortical collecting tubule.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of dexamethasone on segmental phosphate reabsorption in phosphate-deprived rats
Authors: Webster S. K. , Haramati A. , Knox F. G.
Published: December 2017

These experiments were designed to test the hypothesis that avid phosphate reabsorption by the pars recta accounts for the resistance to the phosphaturic effects of acute dexamethasone (DEX) and parathyroid hormone (PTH) infusions in rats fed a low-phosphate diet. Acute infusion of DEX [0.4 mg/(kg X h)] increased the fractional delivery of phosphate (FDPi) to the late proximal tubule from 7.1 +/- 2.1 to 14.4 +/- 3.5%, whereas FDPi to the early distal tubule and urine were not different. PTH alone [1 U/(kg X min)] increased FDPi to the late proximal tubule from 4.0 +/- 1.1 to 15.7 +/- 3.7%, whereas FDPi to the early distal tubule or urine was not different. The combination of DEX and PTH further increased FDPi to the late proximal tubule (32.7 +/- 6.4%) and resulted in an increase in fractional excretion of phosphate (FEPi), in spite of the fact that the FDPi to the early distal tubule was not significantly increased. The increased delivered load of phosphate to the pars recta following inhibition of phosphate transport in superficial proximal convoluted tubules resulted in a comparable increase in phosphate reabsorption in the pars recta, based on linear regression analysis, in rats fed low-phosphate diet but not in rats fed normal phosphate diet. These results demonstrate that acute infusion of DEX or PTH inhibits fractional phosphate reabsorption in the superficial proximal tubule but does not result in an increase in FEPi due at least in part to avid phosphate reabsorption in the superficial pars recta in rats fed low-phosphate diet.(ABSTRACT TRUNCATED AT 250 WORDS)
Proximal tubular reabsorption and Na-K-ATPase activity in remnant kidney of young rats
Authors: Celsi G. , Larsson L. , Aperia A.
Published: December 2017

In rats unilaterally nephrectomized (NX) in infancy, the compensatory growth of the remnant kidney is due first to hypertrophy and hyperplasia, but after 2 wk only to hyperplasia. We studied proximal tubular adaptation (reabsorption, Na-K-ATPase activity, length, and basolateral membrane area) 2 and 8 wk after NX. The rats were NX at 5 days of age. The size of remnant kidney obtained from uninephrectomized rats was 125% at 2 wk and 179% at 8 wk relative to the appropriate time-related controls. Single-nephron glomerular filtration rate in the uninephrectomized group was doubled relative to controls, whereas fractional reabsorption by the proximal tubule was unchanged. Na-K-ATPase activity per millimeter of proximal convoluted tubule (PCT) was significantly increased in the uninephrectomized group relative to controls at 2 but not 8 wk. The area of the basolateral cell membrane per millimeter PCT was unchanged at both 2 and 8 wk, which suggests that the density of enzyme units inserted in the membrane was increased at 2 but not at 8 wk. PCT length was increased at 8 but not at 2 wk. There was a close correlation between total PCT Na-K-ATPase activity and filtered sodium (r = 0.999) and between total PCT Na-K-ATPase activity and PCT sodium reabsorption (r = 0.998). We conclude that the proximal tubule can adapt to an increased filtered load by increasing the density of transporting units or by increasing the tubular length. The latter stage may be attained only in young growing animals.
Dependence of proximal tubule p-aminohippurate secretion on serum proteins and metabolic substrates
Authors: Webb D. E. , Edwards R. M. , Grantham J. J.
Published: December 2017

Renal proximal tubules secrete p-aminohippurate (PAH) and other endogenous anionic metabolites into the urine. The extent to which organic anion excretion is regulated is unknown, but recent studies indicate that peritubular serum proteins may have a role. We determined the relative effects of serum proteins and metabolic substrates (citrate, lactate, and alanine) on net PAH secretion in isolated perfused rabbit S2 proximal tubules. Net PAH secretion was calculated from the bath-to-lumen flux of [3H]PAH and the isotope specific activity. We corrected the flux for the important difference in PAH binding between rabbit serum proteins and bovine serum albumin (BSA); rabbit serum proteins (5.7 g/dl) and BSA (6 g/dl) bound 10 microM PAH 21 and 37%, respectively. BSA had no effect, but rabbit serum proteins reversibly inhibited PAH secretion in the presence of metabolic substrates in the bath (40.8%), the perfusate (42.6%), and both media (31.5%). In the absence of metabolic substrates, rabbit serum proteins decreased PAH secretion by only 16.8%. PAH secretion was inhibited by 1 g/dl rabbit serum proteins as effectively as 5.7 g/dl (30.3 and 31.5%, respectively), indicating that PAH transport is very sensitive to inhibition by rabbit serum proteins. In the absence of rabbit serum proteins, metabolic substrates in the bath had no effect on PAH secretion. We conclude that rabbit serum proteins inhibit basolateral membrane transport of PAH in proximal tubules. Inhibition by serum proteins is enhanced by bath or lumen citrate, alanine, and lactate, suggesting that peritubular plasma proteins and tubule cell metabolism may interact to modulate proximal tubule organic anion secretion and urinary excretion.
Ethane production as a measure of lipid peroxidation after renal ischemia
Authors: Paller M. S. , Hebbel R. P.
Published: December 2017

After renal ischemia, oxygen free radicals are formed and produce tissue injury, in large part, through peroxidation of polyunsaturated fatty acids. We used an in vivo method to monitor lipid peroxidation after renal ischemia, the measurement of ethane in expired gas, to determine the time course of lipid peroxidation and the effect of several agents to limit lipid peroxidation after renal ischemia. In anesthetized rats there was no significant increase in ethane production during 60 min of renal ischemia. During the first 10 min of renal reperfusion, there was a prompt increase in ethane production from 2.9 +/- 1.3 to 6.3 +/- 1.9 pmol/min (P less than 0.05). Ethane production was significantly increased during the first 50 min of reperfusion and then rapidly tapered to base-line levels. Preischemic administration of allopurinol to prevent superoxide radical generation or the superoxide radical scavenger superoxide dismutase prevented the increase in ethane production during postischemic reperfusion. These studies confirm that there is increase lipid peroxidation following renal ischemia that can be prevented by agents which limit the formation or accumulation of oxygen free radicals. This in vivo method for measuring lipid peroxidation could also be employed to study the effects of ischemia on lipid peroxidation in other organs, as well as to monitor lipid peroxidation in other forms of injury.
Lactate increases potassium secretion by perfused rat kidney
Authors: Brezis M. , Spokes K. , Silva P. , Epstein F. H.
Published: December 2017

The effect of exogenous metabolic substrates on K+ secretion was evaluated in the isolated perfused rat kidney in the presence of 2-deoxyglucose and 2-tetradecylglycidic acid to inhibit utilization of glucose and fatty acids from endogenous sources. L-Lactate (15 mM) added to the perfusion medium enhanced renal oxygen consumption (4.0 +/- 1.1 mumol X min-1 X g-1 vs. 2.0 +/- 1.0 without lactate) while decreasing fractional excretion of sodium (19.3 +/- 2.4% vs. 47.3 +/- 1.8). L-Lactate markedly increased the fractional excretion of K+ to 181 +/- 29% compared with 68 +/- 12% without lactate (P less than 0.001). The poorly metabolized isomer D-lactate did not alter these parameters. The addition of alpha-ketoglutarate only slightly increased K+ excretion. In the absence of metabolic inhibitors and in the presence of glucose (5 mM), L-lactate also increased K+ excretion significantly more than did D-lactate (108 +/- 19% vs. 69 +/- 11, P less than 0.02). At the end of 90 min of perfusion with L-lactate medium, K+ concentration in the perfusate dropped from 4.7 +/- 0.05 to 3.2 +/- 0.2 meq/liter (vs. 3.8 +/- 0.1 meq/liter with D-lactate, P less than 0.005) without differences in glomerular filtration rate or sodium excretion. L-Lactate appears to increase K+ secretion by preferential metabolic stimulation of the distal tubule, a process that may help in vivo to prevent hyperkalemia in lactic acidosis.
Interleukin-1 decreases renal sodium reabsorption: possible mechanism of endotoxin-induced natriuresis
Authors: Caverzasio J. , Rizzoli R. , Dayer J. M. , Bonjour J. P.
Published: December 2017

Administration of pyrogen or endotoxins such as Escherichia coli lipopolysaccharide can elicit a marked increase in urinary sodium excretion. This response occurs without any elevation in the filtered load of sodium and it does not appear to be prostaglandin mediated. The various effects produced by endotoxins appear to have interleukin-1 as a common mediator. In the present work, we have studied whether human recombinant interleukin-1 beta (hrIL-1) could affect the renal handling of sodium and thus, could be implicated in natriuretic response to pyrogens or endotoxins. We observed that hrIL-1 intravenously injected into conscious rats provokes a marked increase in sodium excretion. This natriuretic response was not associated with any increase in glomerular filtration rate (clearance of [3H]inulin), nor was it accompanied by significant changes in the urinary excretion of potassium, calcium, or inorganic phosphate. The only concomitant alteration was a decrease in urinary pH. Pretreatment with indomethacin abolished the effect of hrIL-1 on urinary pH but did not modify the natriuretic response. In conclusion, hrIL-1 elicits a selective decrease in tubular sodium reabsorption, which does not appear to involve a change in prostaglandin synthesis. This observation strongly suggests that interleukin-1 could be a key mediator in endotoxin-induced natriuresis.
Cells of origin of the sympathetic renal innervation in rat
Authors: Sripairojthikoon W. , Wyss J. M.
Published: December 2017

Physiological studies are rapidly elucidating the function of the renal nerves; however, the anatomical location of the postganglionic cell bodies that supply the rat kidney has not been fully clarified. The origin of the sympathetic projection to the rat kidney was investigated in the present study by use of the fluorescent dye retrograde transport technique. Application of the dye to the renal nerves resulted in the fluorescent labeling of sympathetic cell bodies in paravertebral [thoracic (T) segment 6 through lumbar (L) segment 4] and prevertebral (renal, greater splanchnic, and celiac) ganglia and along the greater splanchnic nerve. Sympathetic neurons in all of these locations were round to fusiform in shape, 16-40 micron in diameter. They were dispersed uniformly throughout the paravertebral ganglia and splanchnic nerve, but in the celiac and greater splanchnic ganglia, cells projecting to the kidney were clustered near the origin of the renal nerve. In contrast to the cat, in which greater than 50% of the renal sympathetic innervation arises from the prevertebral ganglia, in the rat the majority (greater than 70%) of labeled renal sympathetic neurons were in the paravertebral ganglia, especially T12-L1. The distribution of renal sympathetic neurons in the paravertebral ganglia closely approximates the rostrocaudal distribution of renal afferent cell bodies in the dorsal root ganglia.
Endogenous prostaglandins modulate autoregulation of renal blood flow in young rats
Authors: Chevalier R. L. , Carey R. M. , Kaiser D. L.
Published: December 2017

After uninephrectomy in the young rat, renal blood flow (RBF) increases at normal renal perfusion pressure (RPP) but not at reduced RPP. To evaluate the role of endogenous prostaglandins on these effects, RBF was measured during reduction in RPP in rats that were uninephrectomized within 1 wk of age and studied at 33-41 days of age. After acute cyclooxygenase inhibition, autoregulation improved; RBF was unchanged at normal RPP but increased at lower pressures with concomitant decrease in renal venous plasma renin activity (PRA). Prostaglandin inhibition also improved autoregulatory efficiency in acutely uninephrectomized and sham-operated young rats. Infusion of a thromboxane synthesis inhibitor had no effect on the pressure-flow relationship or on PRA, whereas angiotensin converting enzyme inhibition increased RBF at all measured RPP without affecting autoregulation. We conclude that increased RBF at normal RPP in the uninephrectomized young rat is not maintained by increased prostaglandin synthesis or decreased thromboxane- or angiotensin-dependent vasoconstriction. However, by maintaining increased vasoconstriction at reduced RPP, prostaglandin-dependent renin release reduces autoregulatory efficiency in the young rat.
Chloride transport by the cortical and outer medullary collecting duct
Authors: Schuster V. L. , Stokes J. B.
Published: December 2017

The processes by which chloride is transported by the cortical and outer medullary collecting tubule have been most extensively studied using in vitro microperfusion of rabbit tubules. Chloride appears to be transported by three major mechanisms. First, Cl can be actively reabsorbed by an electroneutral Cl-HCO3 exchanger localized to the apical membrane of the HCO3-secreting (beta-type) intercalated cell. Cl exits this cell via a basolateral Cl channel. This anion exchange process can also operate in a Cl self-exchange mode, is stimulated acutely by beta-adrenergic agonists and cAMP, and is regulated chronically by in vivo acid-base status. Second, Cl can diffuse passively down electrochemical gradients via the paracellular pathway. Although this pathway does not appear to be selectively permeable to Cl, it is large enough to allow for significant passive reabsorption. Third, Cl undergoes recycling across the basolateral membrane of the H+-secreting (alpha-type) intercalated cell. HCO3 exit from this cell brings Cl into the cell via electroneutral Cl-HCO3 exchange; Cl then exits the cell via a Cl channel. Cl transport is thus required for acidification and alkalinization of the urine. Both of these processes exist in the cortical collecting tubule. Their simultaneous operation allows fine tuning of acid-base excretion. In addition, these transport systems, when functioning at equal rates, effect apparent electrogenic net Cl absorption without changing net HCO3 transport. These systems may play an important role in regulating Cl balance.
Inhibition of epithelial Na+ transport by atriopeptin, protein kinase c, and pertussis toxin
Authors: Mohrmann M. , Cantiello H. F. , Ausiello D. A.
Published: December 2017

We have recently shown the selective inhibition of an amiloride-sensitive, conductive pathway for Na+ by atrial natriuretic peptide and 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) in the renal epithelial cell line, LLC-PK1. Using 22Na+ fluxes, we further investigated the modulation of Na+ transport by atrial natriuretic peptide and by agents that increase cGMP production, activate protein kinase c, or modulate guanine nucleotide regulatory protein function. Sodium nitroprusside increases intracellular cGMP concentrations without affecting cAMP concentrations and completely inhibits amiloride-sensitive Na+ uptake in a time- and concentration-dependent manner. In contrast, 8-BrcAMP is without effect on Na+ uptake through the Na+ channel. 1-Oleoyl 2-acetylglycerol (10 micrograms/ml) and phorbol 12-myristate 13-acetate (100 nM), activators of protein kinase c, inhibit Na+ uptake by 93 +/- 13 and 51 +/- 10%, respectively. Prolonged incubation with phorbol ester results in the downregulation of protein kinase c activity and reduces the inhibitory effect of atrial natriuretic peptide, suggesting that the action of this peptide involves stimulation of protein kinase c. Pertussis toxin, which induces the ADP-ribosylation of a 41-kDa guanine nucleotide regulatory protein in LLC-PK1 cells, inhibits 22Na+ influx to the same extent as amiloride. Thus, increasing cGMP, activating protein kinase c, and ADP-ribosylating a guanine nucleotide regulatory protein all inhibit Na+ uptake. These events may be sequentially involved in the action of atrial natriuretic peptide.
Effects of flow rate on proximal tubule ultrastructure
Authors: Maunsbach A. B. , Giebisch G. H. , Stanton B. A.
Published: December 2017

In this study we investigated the ultrastructure of the proximal tubule during alterations in fluid flow to determine whether previously observed changes in solute and water reabsorption may be related to alterations in cell ultrastructure. In each kidney, two proximal tubules (S2 segments) were perfused simultaneously at 5 and 45 nl/min. Subsequently, cell ultrastructure of control and experimental tubules was examined by electron microscopy in combination with morphometry. Changes in flow rate greatly modified the geometry of the tubule epithelium. Enhanced flow increased luminal diameter and decreased cell height. The number of microvilli per square micrometer of luminal epithelial surface area decreased with increased flow rate from a control value of 42.5 to 35.5 at high flow. However, the total number of microvilli per millimeter tubule length did not change. Thus the distance between microvilli was dependent on flow rate and was estimated to be 621, 741, and 904 A in low flow, control, and high flow tubules, respectively. We suggest that increased flow rate, perhaps by altering transepithelial hydrostatic pressure gradients, leads to an increase in the distance between the microvilli and to other alterations in cellular ultrastructure that may contribute to the augmentation of solute and water reabsorption.
Calcium and vitamin D metabolism in spontaneously hypertensive rats
Authors: Hsu C. H. , Yang C. S. , Patel S. R. , Stevens M. G.
Published: December 2017

We have studied the effect of dietary vitamin D restriction on serum levels of vitamin D metabolites in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Both WKY and SHR were fed a vitamin D-deficient or a vitamin D-supplemented diet beginning at 4 wk of age. In vitamin D-supplemented animals, the serum 1,25-dihydroxycholecalciferol [1,25(OH)2D3] concentration of WKY (55.4+/- 6.6 pg/ml, n = 5) was similar to the level of SHR (46.3+/- 5.9 pg/ml, n = 5). Plasma calcium concentration was not different between WKY and SHR. In animals fed a vitamin D-deficient diet, the serum concentration of 1,25-(OH)2D3 of SHR (23.0+/- 1.3 pg/ml, n = 5) was significantly lower than that of WKY (67.6+/- 4.6 pg/ml, n = 5, P less than 0.01). Plasma 25-hydroxycholecalciferol level was markedly decreased in both WKY (3.6+/- 0.5 ng/ml, n = 7) and SHR (2.8+/- 0.4 ng/ml). The SHR, but not the WKY, developed hypocalcemia (WKY, 9.68 mg/dl; SHR, 6.70 mg/dl). Despite hypocalcemia, fasting urinary Ca2+ excretion of SHR exceeded that of WKY. We conclude that the lower 1,25(OH)2D3 level in SHR fed a vitamin D-deficient diet may be due to a defect in the synthesis of 1,25(OH)2D3. The low level of 1,25(OH)2D3 is associated with renal wasting of calcium and hypocalcemia in SHR.
Interorgan glutamine flow in metabolic acidosis
Authors: Welbourne T. C.
Published: December 2017

Acid-base homeostasis depends on glutamine flow from producer organs to those capable of generating bicarbonate. Glutamine oxidation, the prerequisite metabolic transformation, can be expressed by many sites; however, net base generation requires that glutamine flow be directed to a specific organ, the kidney. Normally, glutamine flows from the periphery to the splanchnic bed, providing a major fuel and supporting ureagenesis. Glutamine flow in chronic metabolic acidosis, on the other hand, is rerouted to the kidneys; asymmetrical distribution of NH+4 and HCO3- into the urine and renal vein subserves restoration of alkaline reserves. Clearly, glutamine flows in accordance with physiological demands, yet little is known of the regulatory mechanisms. As a model, chronic metabolic acidosis alters two aspects of this vital flow, its direction and magnitude. Characteristically the direction of flow is away from the splanchnic bed and into the kidneys associated with a marked fall in arterial glutamine concentration, restoring arterial level returns flow to the splanchnic bed sink. Thus glutamine homeostasis is sacrificed to impart direction to interorgan glutamine flow. Although multiple sites contribute to glutamine homeostasis, of great strategic importance is the potent hepatic glutaminase flux activated by portal venous NH+4 fed forward by gut metabolism; local hydrogen ion concentration modulates the effectiveness of this activator. Acute regulation of flow direction can be exerted by the lungs in determining the prevailing pCO2 and cellular acidity; respiratory compensation in chronic acidosis allows the expression of hepatic glutaminase, thereby suppressing arterial glutamine concentration. The enormous magnitude of glutamine flowing from muscle to the kidneys is supported by adaptive increases in glutamine synthetase and mitochondrial glutaminase, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Potassium adaptation: 39K-NMR evidence for intracellular compartmentalization of K+
Authors: Adam W. R. , Koretsky A. P. , Weiner M. W.
Published: December 2017

To investigate the effects of K+ uptake on the intracellular environment, both 39K-nuclear magnetic resonance (NMR) and K+-selective electrodes were used to measure K+ activity with acute K+ loading in control and K+-adapted rats. These results were then compared with tissue K+, measured by flame photometry. There was a lower NMR K+ visibility (ratio of NMR signal to tissue content) in muscle and liver in K+-adapted rats, compared with controls before and after an acute K+ load. This lower K+ visibility in K+-adapted rats was confirmed in liver homogenate with the K+-specific electrode. In liver homogenates from control and K+-adapted rats, addition of RbCl (300 mumol/g) increased the NMR K+ signal more in K+-adapted rats (19 +/- 1.1 mumol/g) than controls (11 +/- 1.0 mumol/g, P less than 0.01). This is consistent with the displacement of K+, by Rb+, from NMR-undetected sites. These results suggest that some 10-15% of intracellular K+ may be within a compartment not detectable by NMR or electrodes and that chronic K+ loading leads to an increased capacity of this compartment.
Time course of proximal tubule response to acute arterial hypertension in the rat
Authors: Chou C. L. , Marsh D. J.
Published: December 2017

Acute hypertension was previously shown to cause partial inhibition of proximal tubule fluid reabsorption in perfused tubules in the rat. If the inhibition also occurs in unobstructed tubules receiving native glomerular filtrate, hypertension should increase end proximal flow rate despite autoregulation of glomerular filtration rate (GFR). We tested this prediction with a videodensitometric method recently developed for measurement of tubular flow rate that does not interrupt flow to the macula densa. Hypertension was induced by increasing total peripheral resistance in rats receiving several hormones at rates designed to maintain high levels of these agents. End proximal flow rate was increased 18% as early as 1.5–2 min following the induction of hypertension and increased over the course of the next 25–30 min to reach values 50% greater than controls as the hypertension was sustained. Whole-kidney GFR and renal blood flow were fully autoregulated. The results confirm that hypertension increases the fluid load to the loop of Henle, and are consistent with an effect on proximal tubule fluid reabsorption. This increase in fluid load could signal the macula densa and contribute to the efficacy of autoregulation; it could also provide a significant fraction of the increased fluid and salt excretion of pressure natriuresis.
The amphibian diluting segment
Authors: Guggino W. B. , Oberleithner H. , Giebisch G.
Published: December 2017

Diluting segments function to reabsorb NaCl and to reduce the osmolality of tubule fluid. These segments in amphibians are important in the conservation of NaCl. The diluting segment of mammals, the thick ascending limb, besides being an important site for the reabsorption of NaCl, supplies the energy that enables the kidney to excrete a concentrated urine. We focus in this review on the mechanisms involved in cellular and paracellular transport of Na+, K+, Cl-, and H+ in the amphibian diluting segment and how the transport of these ions is regulated. Also discussed is the action of loop diuretics and hormones on both transepithelial and cellular function. The large size of amphibian cells and their viability in various artificial conditions have allowed experiments to be performed that are not possible in the mammalian kidney, providing important information on the mechanisms of ion transport common to both mammalian thick ascending limb and amphibian diluting segment.
Passive NaCl transport in the flounder urinary bladder: predominance of a cellular pathway
Authors: Stokes J. B.
Published: December 2017

The urinary bladder of the winter flounder is a high-resistance epithelium that can absorb Na and Cl in an electrically silent manner. This active absorption (mucosa-to-serosa) of NaCl is, apparently uniquely, inhibited by mucosal hydrochlorothiazide (HCTZ). These experiments evaluated the notion that virtually all of the cellular Na and Cl permeation could be inhibited by mucosal HCTZ. Mucosal Ba2+ reduced the transepithelial conductance from 0.74 +/- 0.08 to 0.60 +/- 0.06 mS/cm2. Mucosal HCTZ reduced the serosa-to-mucosa flux (backflux) of Na from 0.70 +/- 0.08 to 0.29 +/- 0.03 mueq.cm-2.h-1 and the backflux of Cl from 1.92 +/- 0.22 to 0.38 +/- 0.03 mueq.cm-2.h-1. The treatment with these two agents caused the sum of the partial ionic conductances for Na and Cl to approximate the measured transepithelial conductance. In response to the imposition of a transepithelial voltage, the HCTZ-insensitive Na and Cl backfluxes behaved largely as predicted by the laws of simple ionic diffusion, although there was still a detectable cellular backflux. As judged from dilution voltages and tracer fluxes, the diffusional (paracellular) pathway(s) is nonselective for Na and Cl. The HCTZ-sensitive cellular Na and Cl backfluxes are dependent on the presence of mucosal Na and Cl. Neither backflux is significantly inhibited by serosal application of commonly used inhibitors of Na or Cl transport. The results demonstrate that the majority of passive Na and Cl flux is via a cellular pathway. The translocation across the apical membrane probably involves the same NaCl cotransport process responsible for NaCl absorption.