bluuebunny/crossref_metadata_2025 huggingface dataset:
Potential role for gluconeogenesis in pyruvate stimulation of H+ transport by turtle urinary bladder
Authors: Schwartz John H.
Published: December 2017

The rate of H+ transport (JH) by turtle bladder is coupled to glucose metabolism by the pentose shunt and can be stimulated in bladders depleted of endogenous substrate by pyruvate. In order to define the pathway of pyruvate metabolism that results in an increment in JH, the effect of an inhibitor of gluconeogenesis, 3-mercaptopicolinic acid (MPL), was examined on pyruvate stimulation of JH, glucose formation, and the rate of pyruvate metabolism. Bladders were incubated in substrate-free media for 18 h. Then either pyruvate or glucose was added to the medium in the presence or absence of 10 μM MPL. The rate of JH was determined by the pH stat technique, Na+ transport from the short-circuit current, and pyruvate metabolism was determined from the rate of 14CO2 production from [14C]pyruvate. The increase in JH in control bladders after pyruvate addition, 155.8 ± 13.6 μmol·h-·g dry wt-, was greater than in MPL-treated bladders, 59.7 ± 13.1 μmol·h-·g dry wt- (P < 0.01). Glucose appearance in the incubation medium was also greater in controls, 0.83 ± 0.16 vs. 0.22 ± 0.07 μmol·h-1·g dry wt- (P < 0.01). MPL had no effect on JH stimulation by glucose. Pyruvate stimulation of Na+ transport, which does not require gluconeogenesis, was not affected by MPL. MPL reduced only that moiety of pyruvate metabolism associated with H+ transport. MPL probably does not inhibit nongluconeogenic pathways of pyruvate metabolism or glucose metabolism itself. From these studies it is suggested that pyruvate stimulation of JH requires gluconeogenesis, and that in part it is the metabolism of glucose that is required for increased rates of JH.

3-mercaptopicolinic acid; acetazolamide; pyruvate metabolism; short-circuit current

Submitted on November 13, 1979

Accepted on April 29, 1980
Magnesium transport in the nephron
Authors: Quamme G. A. , Dirks J. H.
Published: December 2017

Magnesium is filtered at the glomerulus to the extent of 70-80%, of which about 80-95% is reabsorbed by the various nephron segments. Recent evidence from micropuncture and microperfusion experiments has characterized the tubular handling of magnesium. The proximal convoluted tubule reclaims 20-30% of the filtered magnesium, considerably less than the fractional reabsorption of sodium and calcium. The proximal tubule is poorly permeable to magnesium but overall reabsorption is dependent on the filtered load and net water reabsorption. Specific knowledge of magnesium handling in the straight portion of the proximal tubule is lacking. Definitive evidence has been presented to indicate the important role of the thick ascending limb of the loop of Henle. The loop reabsorbs approximately 50-60% of the filtered magnesium or about 80% of that delivered to this segment. In vivo microperfusion studies have shown that elevation of luminal magnesium results in enhanced reabsorption proportional to delivery, whereas elevation of contraluminal magnesium leads to a fall in magnesium transport dependent on the absolute plasma concentration. This suggests a unique magnesium transport interaction on the contraluminal side of the ascending limb membrane that may also involve calcium. Parathyroid hormone increases magnesium reabsorption in the loop; however, its physiological role remains undefined. The distal convoluted tubule reabsorbs only 1-5% of filtered magnesium. Although it is now clear that successive segments of the nephron transport magnesium in different ways, the nature of the cellular mechanisms are unknown. The search for a specific physiological regulator of renal magnesium reabsorption remains unsuccessful. However, recent evidence suggests that overall renal magnesium homeostasis is determined to a large extent by transport in the ascending limb of Henle's loop.
Testosterone: a specific competitive antagonist of aldosterone in the toad bladder
Authors: Rossier B. C. , Geering K. , Gaggeler H. P. , Claire M. , Corvol P.
Published: December 2017

Testosterone (100 nM to 40 microM) antagonized the effect of aldosterone (10 nM) on Na+ transport in the toad bladder measured in vitro as short-circuit current (SCC). Half-maximal inhibition occurred at an antagonist-agonist molar ratio of 150:1. The antagonist action of testosterone was reversed by addition of more aldosterone. The antagonism was specific in the sense that testosterone (20 microM) did not inhibit the response of the SCC to oxytocin (50 mU/ml). By itself, testosterone (up to 20 microM) had no agonist activity on base-line SCC. Finally, testosterone (500 nM to 20 microM) specifically displaced [3H]aldosterone (5 nm) from its cytoplasmic and nuclear binding sites in bladders incubated in vitro at 25 or 0 degrees C and labeled at steady state. There was a significant linear correlation between the effect of testosterone on the aldosterone-dependent SCC and its effect on [3H]aldosterone binding sites in the cytoplasm and in the nucleus. We conclude that 1) testosterone is a specific competitive antagonist of aldosterone, and 2) [3H]aldosterone nuclear and cytoplasmic binding sites could be mineralocorticoid receptors, mediating the action of aldosterone on Na+ transport.
Direct measurement of transepithelial force: an in vivo technique
Authors: Bresler E. H. , Nielsen K. T. , O'Dell R. M. , Cazenavette L. L.
Published: December 2017

A technique for direct in vivo measurement of the intensity of absorptive force generated by an epithelial membrane is described. A quasirigid porous cartridge containing normal saline was placed in isolated intestinal segments of anesthetized rat and connected, via a catheter, to a Statham pressure transducer. Once excess fluid had been absorbed, further fluid absorption was hindered by the nonyielding character of the cartridge, leading to the development of negative (subatmospheric) pressures. Volume expansion with intravenously infused normal saline solution resulted in an abrupt fall in absorptive force, followed by a more gradual recovery to the pre-volume-challenge level. Contraction of intravascular volume by bleeding led to a prompt increment in absorptive force proportional to the amount of blood removed. Return of the blood to the circulation restored absorptive force to the prebleed level. Complete circulatory arrest (death) produced a temporary increment, lasting about 30 min, in absorptive force. Physical mechanisms that may be involved in these alterations of absorptive force are discussed.
Evidence for renal tubular leakage in maleic acid-induced Fanconi syndrome
Authors: Maesaka J. K. , McCaffery M.
Published: December 2017

Micropuncture and microinjection studies were performed in Sprague-Dawley rats 20 h after subcutaneous injection of buffered maleic acid (MA) or buffer alone in experimental and control rats, respectively. Collections were made from earliest and latest accessible portions of proximal tubule (PT). Lissamine green injections and microperfusion of PT demonstrated leakage of lissamine green from late PT sites in MA-treated rats, whereas inulin leakage occurred at a more distal site. Whole kidney GFR was 58% lower in MA-treated rats despite comparable single nephron GFR in PT of both groups. Microinjections of PT with [methoxy-3H]inulin resulted in injected inulin recovery from the contralateral kidney in MA-treated rats of 24.0 +/- 2.0 compared with 4.7 +/- 0.89% in controls, suggesting that tubular leakage of inulin accounted for the lower whole kidney GFR. Net sodium and phosphate transport in early PT was similar in both groups but was decreased in late PT segments in MA-treated rats. Sodium and phosphate excretion in final urine were, however, comparable in both groups. The significantly lower plasma phosphate concentration might account for the blunted phosphaturia in MA-treated rats. These studies demonstrate a segmental effect of MA on 1) tubular leakage to lissamine green from late PT and inulin beyond the late PT, and 2) decreased net sodium and phosphate transport in the PT.
Stimulation of renal magnesium reabsorption by calcitonin in the rat
Authors: Poujeol P. , Touvay C. , Roinel N. , de Rouffignac C.
Published: December 2017

The effect of salmon synthetic calcitonin (CT) on the renal excretion of water and electrolytes was investigated in thyroparathyroidectomized (TPTX) nondiuretic rats. CT did not significantly alter the excretion of either H2O, Na, Ca, phosphate (P), or K, but consistently decreased both fractional and absolute excretion rates of Mg. This latter effect was probably the result of enhanced reabsorption by the loop of Henle. The excretion rates of P and K were either increased or decreased by CT administration; the Mg response on both the whole kidney and loop of Henle was always observed, however, irrespective of the P and K response. In other experiments, the decrease in Mg excretion was still observed when the fall in the filtered load of P and Ca secondary to CT administration was prevented by an appropriate infusion of Ca and P. It is concluded that 1) CT can alter K and P excretion rates but this influence can be prevented by maintaining the filtered load of Ca and P constant, and 2) CT exerts a marked stimulatory effect on Mg reabsorption, presumably by enhancing reabsorption by the thick ascending limb.
Temperature effect on ADH response of isolated perfused rabbit collecting tubules
Authors: Hall D. A. , Grantham J. J.
Published: December 2017

The time course of the water permeability response to synthetic arginine vasopressin (AVP) was examined in isolated perfused rabbit collecting tubules. When experiments were conducted at 37 degrees C, addition of AVP in a concentration of 100 microU/ml increased hydraulic water permeability (Lp) from 18 +/- 4 X 10(-7) to 153 +/- 15 X 10(-7) cm x s-1 x atm-1. However, in contrast to results obtained at 25 degrees C, the Lp immediately decreased in spite of the continued presence of AVP, reaching half the peak value in 67 +/- 6 (SE) min. A similar decline was observed at 37 degrees C when a cyclic 3',5'-adenosine monophosphate analogue was added to the bathing medium. Corticosteroids greatly enhanced the peak water absorption but did not stabilize the subsequent response to AVP at 37 degrees C. A decline in diffusional water permeability measured in the absence of a transtubule osmotic gradient excluded the possible roles of cellular hypotonicity, increased cell volume, or osmotic water absorption in the unstable response to hormone. The peritubular membrane remained highly permeable to water, independent of AVP and temperature. Duration of exposure to 37 degrees C was more important than AVP in determining the unstable response. On the basis of these studies we conclude that isolated rabbit cortical collecting tubules progressively become insensitive to AVP at 37 degrees C, possibly due to alterations in the responsiveness of the urinary plasma membrane to cAMP.
Effects of CO2 and acetazolamide on bicarbonate and fluid transport in rabbit proximal tubules
Authors: Jacobson H. R.
Published: December 2017

Early superficial (SF) and juxtamedullary (JM) proximal convolutions of the rabbit kidney were perfused in vitro to determine the effects of carbonic anhydrase inhibition (10(-4) M acetazolamide) and acute changes in PCO2 (decreases to approximately equal to 15 and increases to approximately equal to 74 mmHg) on potential differences (PD in mV), volume reabsorption (Jv in nl x mm-1 x min-1), and bicarbonate reabsorption (JCO2 in pmol x mm-1 x min-1). At PCO2 37 mmHg early JM exhibited a more lumen-negative PD (-7.5 vs. -5.3), greater Jv (1.13 vs. 0.82), and greater JCO2 (86.7 vs. 44.4) than early Sf. Sf and JM had similar responses to acetazolamide: PD became more negative (-5.2 to -5.9 in SF; -8.8 to -10.1 in JM), Jv decreased (0.92 to 0.68 in SF; 1.11 to 0.76 in JM), and JCO2 decreased (35.7 to 7.7 in SF; 99.2 to 27.4 in JM). Increasing PCO2 to approximately equal to 74 mmHg decreased lumen-negative PD, increased Jv, and increased JCO2 in SF and JM (-5.5 to -4.8, 0.72 to 0.95, and 47.6 to 80.4 in SF; -6.6 to -5.7, 1.19 to 1.47, and 78.0 to 111.3 in JM). Decreasing PCO2 to approximately equal to 15 mmHg increased lumen-negative PD, decreased JCO2, but had no effect on Jv in both segments (-4.9 to -5.8, 51.3 to 6.3, and 0.80 to 0.79 in SF; -7.0 to -7.9, 75.3 to 19.6, and 1.34 to 1.41 in JM). It is concluded that 1) early SF and JM display quantitative heterogeneity, 2) PCO2 changes within the physiologic range produce large changes in HCO3 absorption in early proximal tubules and 3) large changes in HCO3- reabsorption are dissociated from changes in volume reabsorption during hypocapnia.
Relation of ADH effects to altered membrane fluidity in toad urinary bladder
Authors: Kachadorian W. A. , Muller J. , Rudich S. , DiScala V. A.
Published: December 2017

Membrane fluidity, urea permeability, and osmotic water permeability in toad urinary bladder are regularly enhanced by antidiuretic hormone (ADH). In addition, organized intramembranous particle aggregates, which correlate specifically with hormonally stimulated water permeability, are found in granular cell luminal membranes consequent to ADH stimulation. In this investigation ADH-stimulated changes in urea and osmotic water permeability and luminal membrane aggregates at room temperature (24.8 +/- 0.4 degrees C) and in the cold 10.6 +/- 0.2 degrees) were compared with corresponding changes in membrane fluidity, as assessed by n-butyramide permeability. Although a critical level of membrane fluidity is undoubtedly required, the occurrence of aggregates in the luminal membrane is independent of an accompanying hormonally induced change of membrane fluidity. ADH-stimulated osmotic water permeability in toad bladder is also independent of the coincident change in membrane fluidity, and as a process almost certainly involves membrane channels, not a solubility-diffusion process through membrane lipids. For ADH-stimulated transbladder urea movement, channels seem to be involved as well, and the change induced in membrane fluidity by ADH could be an underlying factor in their formation.
Effects of sodium and chloride on potassium transport by the bullfrog kidney
Authors: Sullivan L. P. , Welling D. J. , Rome L. A.
Published: December 2017

We have studied the effect on K transport of reductions in the Na and Cl concentrations of solutions perfusing the isolated bullfrog kidney. We used recently developed techniques for estimating the unidirectional reabsorptive and secretory K fluxes. Reduction of Na and Cl concentrations in the arterial perfusate from 112 and 100 mM to 22 and 10 mM, respectively, inhibited K secretion 82% and K reabsorption 97%. Reduction of only the Na concentration inhibited K secretion 42% but did not affect K reabsorption. Arterial and portal perfusion with 37 mM Na, 23 mM Cl reduced urine Na concentration to 6 mM and Na reabsorption by 59%. However, K secretion rose 88% and reabsorption fell 76%. Arterial and portal perfusates with 37 mM Na, 100 mM Cl reduced urine Na concentration to 2 mM and Na reabsorption by 46%. Still, K secretion was elevated 57% by an increase in urine flow rate. K reabsorption was not reduced. Arterial and portal perfusates with 112 mM Na, 23 mM Cl, and containing SO4 also stimulated K secretion 26% and inhibited K reabsorption 91%. Thus, reduction of perfusate Na concentration to 22 mM inhibited secretion but 37 mM was sufficient to permit stimulation of secretion by low Cl concentrations and by increased tubular fluid flow rate. Reduction of the perfusate Cl concentration stimulated secretion and inhibited reabsorption. We conclude that a minimum level of Na reabsorption is required to maintain K secretion, but above that minimum level changes in the rate of Na reabsorption do not affect the rate of K secretion. The tubular fluid Cl concentration or the rate of Cl reabsorption affects both reabsorption and secretion of K and, therefore, may be an important regulator of the rate of K excretion.
Segmental chloride reabsorption during volume expansion and recovery
Authors: Sheth A. U. , Knight T. F. , Pace E. , Senekjian H. O. , Weinman E. J.
Published: December 2017

Clearance and micropuncture studies were performed in Sprague-Dawley and Munich-Wistar rats to examine the nephron sites of chloride reabsorption in animals undergoing sustained volume expansion (SVE) (10% of body wt) with isotonic saline and in animals in which the extracellular fluid volume was expanded to 10% of body wt over 60 min, after which the sustaining saline volume was abruptly discontinued (recovery) (R). Net sodium and chloride balances were not significantly different in R compared with SVE. The fractional excretion of chloride, however, was significantly lower (2.62 +/- 0.25 vs. 4.18 +/- 0.62%, P less than 0.05). In the Sprague-Dawley rats, chloride delivery to the early distal tubule average 18% in both groups. Chloride delivery to the late distal tubule was significantly lower in R (4.39 +/- 0.79%) than in SVE (8.55 +/- 0.76%, P less than 0.005). In the Munich-Wistar rats, samples were obtained from the late distal tubule and base and tip of the papilla. Chloride delivery to the base did not differ from that to the late distal tubule in either group, but was significantly lower in R compared with SVE. These results indicate that the so-called “post-volume expansion” antinatriuresis is the result, at least in part, of enhanced reabsorption in the distal tubule.
Effect of erythrocytes and globulin on renal functions of the isolated rat kidney
Authors: Swanson J. W. , Besarab A. , Pomerantz P. P. , DeGuzman A.
Published: December 2017

We assessed the effects in isolated perfused rat kidneys of adding globulin or erythrocytes to Krebs-Henseleit bicarbonate perfusate with albumin as its principal source of colloid osmotic pressure during 3 h of perfusion. Colloid osmotic pressure varied between 11 and 58 mmHg. Bovine or human immunoglobulin substituted in part for albumin produced vasodilation, whereas rat erythrocytes added to albumin at a 5% hematocrit caused vasoconstriction. Inclusion of both globulin and erythrocytes in the perfusate was associated with an intermediate response. Kidneys perfused with albumin alone showed progressive decline in GFR, increasing vascular resistance, and increasing proteinuria correlating with kidney weight gain during perfusion. Onset of GFR and resistance changes were delayed and their magnitude decreased by increasing oncotic pressure. Estimated glomerular filtrate protein concentration of albumin-perfused kidneys progressively increased from 20 to 150 mg/dl. The presence of erythrocytes or globulin in the perfusate prevented the increase in vascular resistance and reduced the degree of decrease in GFR seen with albumin alone in the perfusate and reduced the time-dependent increase in proteinuria by 80%. The effects of globulin and erythrocytes on proteinuria were additive. The prevention of changes in hemodynamics, glomerular filtration, macromolecular clearance, subcapsular fluid accumulation, and organ weight gain for up to 5 h of perfusion by adding erythrocytes and globulins to the albumin perfusate suggest that these agents may be necessary for preventing interstitial edema and for maintaining renal function in vitro.
Stimulation of avian renal phosphate secretion by parathyroid hormone
Authors: Wideman R. F. , Braun E. J.
Published: December 2017

Phosphate buffers (ammonium, sodium, potassium, and calcium phosphate, pH 5.5, 7.2, 8.5) and 32P were infused unilaterally into the renal portal systems of intact, parathyroidectomized (PTX), and parathyroid hormone-infused (PTH) domestic fowl to study the secretory flux for inorganic phosphate (Pi). Urine samples were collected simultaneously from both kidneys, with the uninfused kidney serving as a control for the portal-perfused kidney (modified Sperber technique). No consistent unilateral excess of Pi or 32P excretion occurred for any of the experimental groups. For intact birds, fractional 32P excretion by both kidneys (FE32p) was identical to fractional Pi excretion (FEpi) (determined by chemical analysis) and reflected net reabsorption (0.64). However, during PTH infusion, FE32p was 0.82 (net reabsorption) while FEPi was 1.21 (net secretion). These results indicate that a) the peritubular-to-lumen flux for Pi and 32P is a minor component of net tubular transport, regardless of the parathyroid status, counterion availability, or peritubular Pi concentration; b) plasma Pi and 32P enter the tubule lumen predominantly by filtration; c) PTH stimulates tubular Pi secretion; and d) the secreted Pi is derived from an organic or inorganic pool that does not readily equilibrate with infused 32P (or presumably peritubular Pi).
Comparison of three measures of proximal tubular reabsorption: lithium clearance, occlusion time, and micropuncture
Authors: Thomsen K. , Holstein-Rathlou N. H. , Leyssac P. P.
Published: December 2017

Fractional lithium clearance (CLi/CIn), transit time-occlusion time (e-TT/OT), and late proximal tubular fluid-to-plasma inulin ratio [1/(TF/P)In] collected by micropuncture were determined successively in the same rat during Amytal anesthesia. The rats were examined during hydropenia, after partial aortic constriction, or during saline diuresis. There was a linear relationship (r = 0.80) between CLi/CIn and e-TT/OT. The 1/(TF/P)In ratio correlated closely with both CLi/CIn (r = 0.88) and e-TT/OT (r = 0.91) when intraluminal pressure was maintained at the free-flow level during fluid collection. If fluid collection was guided merely by the position of an oil droplet and the luminal diameter, the 1/(TF/P)In data were not correlated with either CLi/CIn or e-TT/OT. Over a wide range of proximal absolute and fractional reabsorption rates the technically simpler lithium clearance and TT/OT methods may provide data on proximal fractional reabsorption that are as accurate and reliable as data obtained by pressure-controlled micropuncture collection. Micropuncture carried out without pressure control provides highly inaccurate data and is clearly inferior to the other methods. These results are consistent with the possibility that lithium is reabsorbed exclusively by the proximal tubules, 17-20% being reabsorbed by the pars recta.
Homocellular regulatory mechanisms in sodium-transporting epithelia: avoidance of extinction by “flush-through”
Authors: Schultz S. G.
Published: December 2017

In recent years electrophysiologic studies on several sodium-transporting epithelia have uncovered two “homocellular” (intrinsic) regulatory mechanisms that appear to protect the absorptive cells from marked changes in sodium and potassium content in response to rapid and wide-ranging physiologic variations in the rate of transcellular sodium transport. These are: 1) an inverse relation between intracellular sodium activity and the sodium conductance of the apical (mucosal) membrane, and 2) a parallel relation between the rate of sodium extrusion from the cell across the basolateral membrane (“pump activity”) and the conductance of that barrier to potassium. The purpose of this review is to document these homocellular regulatory mechanisms, discuss their physiologic significance, and speculate on possible underlying mechanism(s).
Luminal influences on potassium secretion: chloride replacement with sulfate
Authors: Velazquez H. , Wright F. S. , Good D. W.
Published: December 2017

Electrolyte transport by the renal distal tubule of rats was studied by in vivo continuous microperfusion to determine whether replacing luminal chloride with sulfate would stimulate net potassium secretion. Results in a first series of experiments showed that replacing all Cl in the perfusion fluid with SO4 reduced net Na absorption, reversed the direction of net Cl transport from net absorption to net secretion, increased the lumen-negative transepithelial voltage, and increased net K secretion. In a second series of experiments adding NaCl to a perfusion fluid containing SO4 increased net Na absorption, reversed the direction of net Cl transport from net secretion to net absorption, decreased the transepithelial voltage, and decreased net K secretion. In a third series of experiments addition of 10(-6) M amiloride to a SO4-containing perfusion fluid reduced the transepithelial voltage but did not prevent the increase in K secretion, indicating that the changes in K secretion cannot be explained solely by changes in electrical driving forces. Since net fluid absorption was controlled, the changes in K secretion cannot be attributed to solvent drag effects. In all three series of experiments the rate of net K secretion was increased when luminal Cl concentration was reduced to less than 10 mM. The results suggest the existence of a cotransport system mediating K and Cl absorption by the distal tubule. Inhibition of K absorption by low lumen Cl may contribute to the increased net K secretion seen when nonchloride anions are present in distal fluid.
Renal handling of dopa, dopamine, norepinephrine, and epinephrine in the dog
Authors: Ball S. G. , Gunn I. G. , Douglas I. H.
Published: December 2017

The uptake and excretion of endogenous dopa, dopamine, norepinephrine, and epinephrine by the kidney were studied. Blood samples were taken from the aorta at the origin of the renal artery and from the renal vein during a timed urine collection in each of six anesthetised greyhound dogs. Arterial plasma dopa (1,043 +/- 129 pg/ml) and epinephrine (218 +/- 96 pg/ml) were consistently higher than venous levels of dopa (591 +/- 80) and epinephrine (54 +/- 16 pg/ml), showing extraction of these by the kidney, whereas arterial plasma norepinephrine (329 +/- 89 pg/ml) and dopamine (64 +/- 9 pg/ml) were lower than the venous levels of norepinephrine (695 +/- 161 pg/ml) and dopamine (239 +/- 45 pg/ml), indicating secretion of these catecholamines into the circulation. The dopa extracted did not appear in the urine. Norepinephrine (7.2 +/- 1.7 ng/min), epinephrine (4.5 +/- 1.7 ng/min), and dopamine (3.2 +/- 0.7 ng/min) were excreted in the urine. These rates of urinary excretion could be accounted for by glomerular filtration and tubular secretion of the three catecholamines. The kidney extracts circulating dopa. It extracts and excretes epinephrine, norepinephrine, and dopamine, and, in addition, secretes both dopamine and norepinephrine into the circulation. These observations emphasize the important relationship between renal function and the peripheral sympathetic nervous system.
Aldosterone binding in isolated tubules I. Biochemical determination in proximal and distal parts of the rabbit nephron
Authors: Farman N. , Vandewalle A. , Bonvalet J. P.
Published: December 2017

Microbiochemical methods were applied to proximal tubules (PCT) and a mixture of distal and cortical collecting tubules (D + C) of rabbit kidney in order to define aldosterone binding sites. For each experiment, after incubation of kidney pyramids with [3H]aldosterone ([3H]A), either alone or in the presence of an excess unlabeled A, 100-150 mm of both categories of tubules were microdissected using collagenase. Specific binding was determined on the nuclear fraction of each sample. Aldosterone concentrations ranged from 2 X 10(-9) to 4.5 X 10(-8) M. No specific binding was detectable in PCT. Specific binding in D + C increased rapidly as a function of [3H]A concentration up to 5 X 10(-9) M and then more slowly. No plateau was reached. Both the absence of saturation of the binding curve and the curvilinear aspect of the Scatchard plot suggested the presence of two binding sites, one of high affinity, presumably a mineralocorticoid site, and the other of lower affinity, possibly a glucocorticoid site. These experiments suggest that the distal structures of the nephron, located in the cortex, are the main sites of binding of aldosterone and contain a high number of specific binding sites for this hormone.
Thromboxane B2 and prostaglandin E2 in the rat kidney with unilateral ureteral obstruction
Authors: Whinnery M. A. , Shaw J. O. , Beck N.
Published: December 2017

The production of prostaglandin E2- (PGE2) like and thromboxane A2-(TXA2) like substances is increased after release of unilateral ureteral obstruction (UUO) for 3 days in the isolated perfused rabbit kidney. It has been postulated that this increase in TXA2 biosynthesis might contribute to the development of vasoconstriction in the obstructed kidney. In the present studies, the production of TXA2 and PGE2 in the kidney was further investigated in rats after UUO for 2-18 h. Radioimmunoassay was used to determine thromboxane B2 (TXB2), a chemically stable metabolite of TXA2, and PGE2 production during the incubation of renal slices in vitro. Unlike previous studies, an increase in TXB2 and PGE2 production was demonstrable in the obstructed kidney even in the absence of pharmacological stimulation by bradykinin or angiotensin II. The effect of UUO on prostaglandin production differed in the different anatomical parts of the kidney. In the papilla, production of both TXB2 and PGE2 was increased in the obstructed kidney. In the cortex, however, UUO had a stimulatory effect only on TXB2 production but not on PGE2 production. The increase in TXB2 and PGE2 production was demonstrable as early a 2 h (tested) after ureteral obstruction. Prolongation of ureteral obstruction for 18 h diminished the stimulatory effect of UUO on PGE2 production but not on TXB2 production.
Membrane fluidity and enzyme activities in brush border and basolateral membranes of the dog kidney
Authors: Le Grimellec C. , Giocondi M. C. , Carriere B. , Carriere S. , Cardinal J.
Published: December 2017

The physical state of membrane lipids and relationships with the activity of Na+-K+-ATPase and alkaline phosphatase were studied in basolateral and brush border membranes of the dog kidney. Fluorescence polarization and electron spin resonance experiments demonstrate that basolateral membranes are much more fluid than brush border membranes. This can be accounted for by a difference in fluidity of the lipid part of the membranes. Broad (43-17 degrees C) thermotropic transitions are observed in liposomes made from total lipid extracts of brush border and basolateral membranes. Fluorescence data strongly suggest that thermotropic transitions also occur in intact membranes and that a change in membrane physical state may take place around the physiological temperature. A nonlinear Arrhenius plot for the Na+-K+-ATPase activity in basolateral membranes (breakpoint 21 degrees C) provides additional support for the existence of a lipid liquid leads to gel transition in antiluminal plasma membranes. A break in the Arrhenius plot of alkaline phosphatase activity is also observed but at a temperature significantly higher (26 degrees C) than that of the end of the thermotropic transition. "Room temperature" appears as a critical zone for lipid physical state and activities of both enzymes.
Voltage-dependent calcium movement across the cortical collecting duct
Authors: Bourdeau J. E. , Hellstrom-Stein R. J.
Published: December 2017

Cortical collecting ducts were dissected from rabbit kidneys and perfused in vitro. Unidirectional transepithelial calcium fluxes from bath-to-lumen and lumen-to-bath were measured with 45Ca. Transepithelial voltage was varied over a wide range by pharmacologic manipulations. With lumen-negative voltages net calcium secretion from bath to lumen, which varied directly with the voltage, was observed. At voltages near 0 there was no measurable net flux. When the voltage was made positive, the direction of net calcium transport reversed (i.e., absorption from lumen to bath). Calcium permeability, calculated from the dependence of net flux on voltage, was 1.4 X 10(-7) cm/s, which is less than 2% of the calcium permeability previously determined in the cortical thick ascending limb of Henle's loop. Analysis of the calcium flux ratios revealed apparent interdependence of the bidirectional fluxes consistent with exchange diffusion but no evidence for active calcium transport. We conclude that there is a small, but measurable, component of passive net calcium flux driven by the transepithelial voltage across the cortical collecting duct.
Abnormal tubular adaptation to dietary Pi restriction in X-linked hypophosphatemic mice
Authors: Muhlbauer R. C. , Bonjour J. P. , Fleisch H.
Published: December 2017

The renal handling of inorganic phosphate (Pi) is in part under the control of a powerful mechanism that is independent of parathyroid hormone and has the ability to enhance net tubular Pi reabsorption in response to a reduction in the Pi supply. The decreased renal reabsorption of Pi, the salient feature of the human disease X-linked hypophosphatemia, could be due to a loss of this adaptive capability of the tubular Pi transport system. To investigate this hypothesis, mutant hypophosphatemic (HYP) mice were used as a model of the human disease. Male HYP mice and normal littermates were subjected to high (0.75 g/100 g), low (0.25 g/100 g), or very low (0.03 g/100 g) phosphorus diets for periods varying between 1 and 20 days. Then the overall tubular Pi transport capacity was assessed by determining the maximal net Pi reabsorption per unit volume of glomerular filtrate (max TRPi/ml GF). The results indicate that the marked enhancement of max TRPi/ml GF, which is observed in normal mice after the first day of Pi restriction, is completely absent in HYP mice. In chronically thyroparathyroidectomized animals, 10 days of low phosphorus diet stimulated conspicuous max TRPi/ml GF in normal mice, whereas the same regimen did not significantly change the Pi reabsorptive capacity of HYP counterparts. The results of this study suggest that X-linked hypophosphatemia is a disease with a defect in the mechanism responsible for the adaptation of the tubular Pi transport system to Pi restriction.
Phosphate transport in the light segment of the rabbit cortical collecting tubule
Authors: Shareghi G. R. , Agus Z. S.
Published: December 2017

The mode and mechanism of phosphate transport in the light portion of the rabbit cortical collecting duct were studied with isolated tubular perfusion. Control studies (n = 48) revealed a mean transepithelial potential difference (PD) of -16.5 +/- 1.3 mV and net phosphate absorption (JPO4) of 0.58 +/- 0.07 pmol.mm-1.min-1. To characterize transport, the effects of flow rate, ouabain, amiloride, and phosphate concentration, and parathyroid hormone (PTH) were analyzed. There was a significant linear relationship between JPO4 and flow rate (n = 48) (r = 0.71, P less than 0.025). Increasing the difference between lumen and bath phosphate concentration from -8.0 to +8.0 mg/dl was associated with a stepwise increase in JPO4 from -0.18 +/- 0.02 to 0.93 +/- 0.05 pmol.mm-1.min-1. PTH had no effect on JPO4. To assess the effects of PD, the tubules were treated with either amiloride (n = 6) or ouabain (n = 7). JPO4 fell significant in both circumstances with reduction of PD, although there remained significant residual transport following amiloride addition. The data demonstrate significant phosphate transport in this segment that is independent of PTH and altered by transepithelial electrical and concentration gradients as well as flow rate.
Renal sugar transport in the winter flounder. VI. Reabsorption of D-mannose
Authors: Pritchard J. B. , Booz G. W. , Kleinzeller A.
Published: December 2017

The transport of D-mannose (Man) in flounder kidney was studied using renal clearance techniques in vivo and brush border membrane (BBM) vesicles in vitro. At plasma concentrations of 50-100 microM Man, the winter flounder (Pseudopleuronectes americanus) reabsorbed up to 70% of the filtered sugar. Man phosphates, but not free Man, accumulated in renal cells. Reabsorption of Man was reduced by phlorizin, D-glucose, methyl-alpha-D-glucoside, methyl-alpha-D-mannoside, and 2-deoxy-D-glucose. In BBM vesicles a Na+-dependent, phlorizin-sensitive overshoot in Man uptake (10 microM) was seen. Na+-dependent Man uptake was saturable, with an apparent Km of 127 microM. The transport properties for Man were identical in BBM vesicles from the winter flounder and southern flounder (Paralichthys lethostigma). The transport specificity was determined by cis-inhibition and trans-stimulation experiments with BBM. Glucose, galactose, 1,5-anhydro-D-mannitol (i.e., 1-deoxymannose), 2-deoxy-2-fluoro-D-glucose, and methyl-alpha-mannoside were shown to share the carrier-mediating mannose transport. 2-Deoxyglucose, methyl-alpha-2-deoxy-D-glucoside, and both the isomers (alpha and beta) of methyl-D-glucoside did not. In contrast, alpha-methyl-D-glucoside inhibited D-glucose transport both in vivo and in BBM vesicles. It is concluded that Man reabsorption in the flounder occurs via a Na+-cotransport system that also handles glucose but that differs from the glucose/methyl-alpha-D-glucoside reabsorptive pathway in that 1) an oxygen on C-1 is not required, and 2) an axial configuration for -OH on C-2 (C1 conformation) is readily accommodated.
Effect of adrenal enucleation on inner medullary collecting duct function in the rat
Authors: Bengele H. H. , Alexander E. A.
Published: December 2017

After adrenal enucleation rats have an impaired ability to excrete a salt load. From micropuncture studies comparing data obtained from the late distal collection site and the urine, it has been suggested that this antinatriuretic effect occurs along the collecting duct. These studies are indirect, however, and cannot evaluate the contribution of deep nephrons. We have performed studies directly measuring inner medullary collecting duct (IMCD) function in saline-loaded rats 6 days after adrenal enucleation (AE). The fraction of filtered fluid, sodium, chloride, and potassium was analyzed as a function of IMCD length. In six AE rats 35% of the fluid, 35% of the sodium, and 31% of the chloride delivered to the IMCD was reabsorbed. In six saline-loaded control rats, however, no statistically significant net reabsorption of fluid sodium, or chloride was detected. Net potassium secretion along the IMCD was found in both AE and control rats. No difference between groups was noted, and net addition accounted for 17% of the potassium excreted. We conclude that after AE, the excretion of fluid, sodium, and chloride is impaired during saline expansion because of enhanced reabsorption along the IMCD. AE does not affect potassium handling along the IMCD or potassium excretion.
Regulation of PTH receptor-adenylate cyclase system of canine kidney: influence of Mn2+ on effects of Ca2+, PTH, and GTP
Authors: Bellorin-Font E. , Tamayo J. , Martin K. J.
Published: December 2017

Metal ions play important roles in the regulation of the activation of adenylate cyclase. Previous studies have suggested that an important site of action of metal ions is at or closely related to the nucleotide regulatory protein. The present studies examine the nature of the regulation of enzyme activity by divalent cations and the influence of Mn2+ on hormone binding and stimulation of adenylate cyclase. Studies were performed in canine renal cortical membranes. Substitution of Mg2+ by Mn2+ was associated with a progressive decline in the ability of GTP or PTH to stimulate adenylate cyclase activity. Mn2+ did not alter specific binding of an iodinated PTH analogue. However, in spite of the loss of guanine nucleotide stimulation of enzyme activity, the effects of guanine nucleotide on PTH binding were not altered in the presence of Mn2+. Substitution of Mg2+ by Mn2+ abolished the inhibitory effect of Ca2+ on basal adenylate cyclase activity. Similarly, the effects of GTP or PTH to enhance the inhibitory effects of Ca2+ on enzyme activity were abolished in the presence of Mn2+. Since Mg2+ and Ca2+ compete for a common allosteric site and Mn2+ abolished the effects of these cations, it would appear that Mn2+ also competes for the binding site of Mg2+ and Ca2+. The present studies demonstrating that Mn2+ does not affect hormone binding or the actions of guanine nucleotides on hormone binding yet totally eliminates the effect of GTP on enzyme activity indicate that the effect of Mn2+ occurs at the level of the interactions of the nucleotide regulatory component with the catalytic unit. In addition, these data suggest that there are two functionally distinct sites of guanine nucleotides with different ionic requirements.
Effect of luminal bicarbonate concentration on proximal acidification in the rat
Authors: Alpern R. J. , Cogan M. G. , Rector F. C.
Published: December 2017

The effect of luminal bicarbonate concentration on proximal tubular acidification was studied. Rat proximal convoluted tubules were perfused in vivo with solutions of varying bicarbonate concentration, and bicarbonate absorption was measured using microcalorimetry. Bicarbonate absorption was found to increase linearly with mean luminal bicarbonate concentrations up to 45 mM, but above this level it showed evidence of partial saturation. Bicarbonate permeability was measured and found to be 2.6 +/- 0.3 x 10(-7) cm2/s. Using this permeability, net bicarbonate absorption could be divided into two parallel components, both sensitive to luminal bicarbonate concentration: 1) proton secretion and 2) a passive bicarbonate leak. Proton secretion, when examined as a function of luminal bicarbonate concentration, exhibited saturation kinetics with an apparent Km of 16 mM and a Vmax of 200 pmol . mm-1 . min-1.
Effects of saline on continuously recorded filtration fractions in cat kidney
Authors: Rasmussen S. N. , Nissen O. I.
Published: December 2017

The radioactivity of [51Cr]EDTA and [125I]albumin in arterial and in deep and superficial renal venous blood was continuously measured in an extracorporeally recirculating system. The filtration fraction of plasma in the superficial (FFs) and in the deep (FFD) venous drainage area was computed every 100 s. Following infusion of Ringer fluid a decrease in the FFD/FFs ratio was observed--mainly due to a fall in FFD. The decrease in the FFD/FFs ratio was more pronounced with infusion of Ringer fluid directly into the renal artery than with infusion at the same rate (1.0-1.5 ml . min-1) into a jugular vein, showing that a direct renal effect is involved. The sensitivity of the FFD/FFs reaction is high, as the fluid loads given were moderate. The fall in FFD may be due to a preferential increase in medullary blood perfusion, which, by wiping out the medullary hyperosmolality, promotes diuresis.
Ketone body effects on glutamine metabolism in isolated kidneys and mitochondria
Authors: Goldstein L. , Solomon R. J. , Perlman D. F. , McLaughlin P. M. , Taylor M. A.
Published: December 2017

beta-Hydroxybutyrate (but not acetoacetate) caused marked inhibition of ammonia production and glutamine extraction in isolated perfused kidneys from normal rats. Glutamine synthesis was not affected by beta-hydroxybutyrate (BHB). Measurement of metabolite levels in freeze-clamped kidneys showed that BHB increased glutamine concentration, decreased ammonia concentration, and reduced the mitochondrial NAD+/NADH ratio (calculated) in perfused kidneys. BHB inhibited flux through the glutamate dehydrogenase pathway, probably as a result of reduction in the NAD+/NADH ratio, in isolated renal mitochondria. In isolated perfused kidneys from acidotic rats, ammonia production and mitochondrial NAD+/NADH were both elevated and BHB did not inhibit renal ammoniagenesis. Although ammonia production in the acidotic kidneys was not directly related to the mitochondrial NAD+/NADH ratio, the elevation of this ratio may have permitted a normal rate of oxidation of glutamine end products--which is essential for maintaining the elevated ammoniagenesis--to take place in the presence of BHB.
Effects of acute acid-base disturbances on K+ delivery to the juxtamedullary end-descending limb
Authors: Roy D. R. , Blouch K. L. , Jamison R. L.
Published: December 2017

Effects of acute-base disturbances on fractional delivery of potassium to the juxtamedullary end-descending limb were examined by micropuncture in the rat to test the hypothesis that potassium is reabsorbed from the collecting duct and is secreted in juxtamedullary pars recta or descending limb in the renal medulla. In metabolic acidosis, fractional potassium delivery was only slightly reduced compared with control values and was a function of potassium excretion, as the hypothesis predicts. Fractional potassium delivery was sharply reduced both in respiratory acidosis and metabolic alkalosis and was no longer a function of potassium excretion. Although seemingly inconsistent with the recycling hypothesis, the latter finding may be reconciled by the following observations. In respiratory acidosis, vasa recta blood flow nearly doubled, which would lead to vascular washout of interstitial potassium. In metabolic alkalosis, flow rate in the pars recta or descending limb was reduced by 28%, which would limit transepithelial potassium addition. The results indicate complex effects of acid-base disturbances on fractional potassium delivery to the end-descending limb, which can be unified by postulated changes in transepithelial potassium concentration differences across the juxtamedullary pars recta or descending limb. An unexpected observation emerged--fractional delivery of water to the end-descending limb declined as a function of plasma bicarbonate concentration when all groups were combined.
Autoradiographic study of aldosterone and dexamethasone binding in isolated glomeruli of rabbit kidney
Authors: Farman N. , Vandewalle A. , Bonvalet J. P.
Published: December 2017

Specific binding of tritiated aldosterone ([3H]A) and dexamethasone ([3H]Dex) has been investigated in glomeruli isolated from rabbit kidney by microdissection, using an autoradiographic method on dry film. At low physiological concentrations of [3H]A (0.2-2 nM), no specific binding was detected. At high concentration (24 nM), a low specific binding was found in cytoplasm (2.5 specific silver grains/100 micrometers2) and nuclei (3.7), which was about 10 times lower than in distal tubule. No difference was found between superficial and juxtamedullary glomeruli. At 2.4 nM [3H]A, no aldosterone binding was present in glomerular arterioles. Nuclear binding of [3H]Dex was low at 3 nM (6.4 specific silver grains/100 micrometers2) and reached 23.6 at 100 nM without significant cytoplasmic binding. Here again, this binding was much lower than in distal structures of the nephron. In the few arterioles obtained, a clear specific nuclear binding was observed. We conclude that the glomerulus is probably not a target structure for aldosterone. The existence of a specific binding of dexamethasone, although lower than in the distal tubule, raises the problem of its physiologic significance.
Renal hemodynamic responses to increased renal venous pressure: role of angiotensin II
Authors: Kastner P. R. , Hall J. E. , Guyton A. C.
Published: December 2017

Studies were performed to quantitate the effects of progressive increases in renal venous pressure (RVP) on renin secretion (RS) and renal hemodynamics. RVP was raised in 10 mmHg increments to 50 mmHg. Renin secretion rate increased modestly as RVP was increased to 30 mmHg and then increased sharply after RVP exceeded 30 mmHg. Glomerular filtration rate (GFR), renal blood flow (RBF), and filtration fraction (FF) did not change significantly when RVP was elevated to 50 mmHg. GFR and RBF were also measured after the renin-angiotension system (RAS) was blocked with the angiotensin converting enzyme inhibitor (CEI) SQ 14225. After a 60-min CEI infusion, RBF was elevated (32%), GFR was unchanged, FF was decreased, and total renal resistance (TRR) was decreased. As RVP was increased to 50 mmHg, GFR and FF decreased to 36.3 and 40.0% of control, respectively, RBF returned to a value not significantly different from control, and TRR decreased to 44.8% of control. The data indicate that the RAS plays an important role in preventing reductions in GFR during increased RVP because blockade of angiotensin II (ANG II) formation by the CEI results in marked decreases in GFR at high RVPs. The decreases in GFR after ANG II blockade and RVP elevation were not due to lack of renal vasodilation, since TRR was maintained below while RBF was maintained either above or at the pre-CEI levels.