bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the apparent transport constants for urate absorption in the rat proximal tubule
Authors: Sansom S. C. , Senekjian H. O. , Knight T. F. , Babino H. , Steplock D. , Weinman E. J.
Published: December 2017

Using continuous-flow luminal microperfusion techniques, the influence of the intraluminal urate concentration on urate absorption was determined in the rat proximal tubule. When the estimated contribution of passive permeation was accounted for, the “active” component of urate absorption demonstrated saturation kinetics. The apparent Km was 0.17 mM and the Vmax 0.31 pmol.min-1.mm-1. These transport constants were similar when derived from either a water-absorbing or steady-state equilibrium perfusion solution. The reflection coefficient was determined in studies employing the techniques of simultaneous capillary and luminal microperfusion. Both perfusion solutions contained p-chloromercuribenzoate to inhibit active urate transport. In the presence or absence of an osmole gradient imposed across the tubule, the reflection coefficient for urate averaged 0.94. These studies provide evidence that urate absorption in the rat proximal tubule is a carrier-mediated process. They also provide independent confirmation of the passive flux coefficient derived in prior studies. Finally, the results suggest that solvent drag would have little effect on urate absorption.
Effects of sodium intake and Goldblatt hypertension on renin release in rat kidney slices
Authors: Naftilan A. J. , Oparil S.
Published: December 2017

The effects of altering sodium intake and inducing two-kidney, one-clip Goldblatt hypertension in the male Sprague-Dawley rat on renin release (RR) from renal cortical slices were examined. The low sodium diet significantly elevated plasma and kidney renin activity (KRA) and base-line renin release (BRR). KRA and BRR in the unclipped kidney of Goldblatt hypertensive rats were suppressed; KRA and BRR in the contralateral clipped kidney were comparable to values in normotensive animals fed a basal diet. Regression analysis of BRR vs. KRA for all kidneys studied yielded an r value of 0.728 for a linear model (y = a + bx) and 0.831 for a power model (y = axb), indicating that BRR is dependent on renal renin stores over a wide range of KRA, and suggesting that BRR may reach a maximal value. Percent inhibition of RR by angiotensin II (AII) and percent stimulation of RR by isoproterenol were the same in high, low, and basal salt states, while absolute changes in RR and changes in RR expressed as percent of renin stores released per hour were less in the high salt state, suggesting that isoproterenol-induced stimulation and AII-induced inhibition of RR are dependent on renal renin stores.
Effect of calcium on prostaglandin E2 release in dogs
Authors: Okahara T. , Abe Y. , Imanishi M. , Yukimura T. , Yamamoto K.
Published: December 2017

Prostaglandin E2 (PGE2) concentration in arterial and renal venous plasma was determined by radioimmunoassay in anesthetized dogs, and the PGE2 secretion rate was calculated. Intrarenal arterial infusion of CaCl2 (0.68 meq/min) resulted in a biphasic effect on renal blood flow (RBF) and an initial increase followed by a gradual decrease below the preinfusion level. PGE2 secretion rate increased from 7.2 +/- 4.4 to 95 +/- 28 ng/min, with a marked increase of RBF after 3 min of CaCl2 infusion. An equivalent amount of NaCl infused into the renal artery did not affect either the RBF or the PGE2 secretion rate. One-tenth the dose of CaCl2 (0.068 meq/min) infused into the renal artery did not increase either RBF or PGE2 secretin rate, and the RBF gradually decreased after infusion. The transient renal vasodilation observed during infusion of a high dose of CaCl2 ceased with the combined intrarenal infusion of verapamil (100 micrograms/min), and was also abolished by pretreatment with indomethacin (5 mg/kg i.v.). Infusion of CaCl2 (0.68 meq/min) into the femoral artery did not enhance the PGE2 secretion rate from the hindlimb, and femoral blood flow decreased immediately after the infusion. These results suggest tht the renal vessels as well as other resistance vessels are essentially constricted by calcium and that endogenous PGE2 released by calcium may modify this renal vasoconstriction.
Effect of low-level renal nerve stimulation on renin release from nonfiltering kidneys
Authors: Holdaas H. , DiBona G. F. , Kiil F.
Published: December 2017

The mechanism whereby renal nerves influence the renin-release response to aortic constriction was examined in a nonfiltering ureter-occluded kidney preparation in anesthetized dogs. The kidney was rendered nonfiltering by a combination of mannitol infusion and ureteral occlusion. Suprarenal aortic constriction reduced renal perfusion pressure to 61 +/- 7 mmHg and increased renin release from 16.7 +/- 4.1 to 26.1 +/- 6.0 U/min. At normal renal perfusion pressure, low-frequency renal nerve stimulation (0.25 Hz) increased renin release by 11.6 +/- 4.2 to 25.1 +/- 7.6 U/min. The effect of combined low-level renal nerve stimulation and aortic constriction on renin release was additive; renin release increased by 24.6 +/- 6.5 to 39.5 +/- 7.3 U/min. Propranolol or metoprolol, administered intrarenally at 2 microgram . min-1 . kg-1, abolished the renin-release response to low-level renal nerve stimulation at normal renal perfusion pressure. These data provide evidence that low-frequency renal nerve stimulation influences the renin-release response to reduction in renal perfusion pressure in a nonfiltering ureter-occluded kidney with an inoperative macula densa receptor mechanism. The neural effect on renin release at normal renal perfusion pressure is mediated via beta 1-adrenoceptors probably located on the juxtaglomerular granular cells.
Hypotensive effect of water restriction in the two-kidney one-clip hypertensive rat
Authors: Leenen F. H. , de Jong W.
Published: December 2017

In two-kidney one-clip hypertensive rats we evaluated the effect of water restriction on the development and maintenance of severe hypertension (systemic blood pressure 200-230 mmHg). After application of renal arterial clips in rats allowed access to water for 1 or 2 h daily, BP stabilized at 180-190 mmHg. No increase in water intake occurred and plasma renin activity(PRA) (measured before the drinking period) was significantly below the levels observed in ad libitum-drinking hypertensive rats. In rats administered 4 ml water/100 g body weight twice daily by gavage, development of hypertension was more clearly suppressed. Blood pressure increased slowly and reached levels of only 150-170 mmHg. Furthermore, PRA was significantly lower in this group compared with ad libitum-drinking hypertensive animals. In rats with established (4-5 wk) renal hypertension, restriction of water intake to 1 or 2 h daily resulted in a rapid decrease in BP of about 30 mmHg. Daily administration of Pitressin tannate to hypertensive rats allowed free access to water induced a similar decrease in BP as well as suppression of PRA. These results indicate that the hypotensive effect of water restriction in the two-kidney one-clip hypertensive rat model may be mediated, at least in part, through elevated circulating levels of vasopressin that subsequently inhibit renin release.
Renal handling of gentamicin by the Munich-Wistar rat
Authors: Sheth A. U. , Senekjian H. O. , Babino H. , Knight T. F. , Weinman E. J.
Published: December 2017

Free-flow micropuncture studies were performed in the Munich-Wistar rat to determine the nephron sites of gentamicin transport. The rats were infused with radiolabeled gentamicin and were volume-expanded with either isotonic sodium chloride or sodium bicarbonate. The fractional delivery of ultrafilterable gentamicin (FD) out of the superficial proximal tubule averaged 75% in both groups of animals. FD to the superficial distal tubule averaged 58.1 +/- 2.1% in saline-infused and 91.6 +/- 5.3% in bicarbonate-infused animals. FD to Henle's loop was 118.2 +/- 8.8 and 124.3 +/- 8.1% in saline- and bicarbonate-infused animals, respectively. FD to the base and tip of the papilla was not significantly different between the two groups and averaged 97.3 +/- 2.9 and 96.1 +/- 3.0% in the saline-infused and 100.5 +/- 2.6 and 94.3 +/- 2.8% in the bicarbonate-infused animals. FD to the base of the papilla was significantly lower than that to the loop of Henle in both groups. These studies indicate that gentamicin undergoes net reabsorption in juxtamedullary proximal tubules. Expansion of the extracellular fluid volume with saline or bicarbonate results in differing rates of gentamicin delivery to the superficial distal tubule but not to the base of the papilla. These findings suggest a significant degree of nephron heterogeneity for gentamicin transport in the rat kidney.
Aldosterone and the enhanced natriuresis of hypertonic infusions in the dog
Authors: Childers J. W. , Schneider E. G.
Published: December 2017

The purpose of this study was to determine whether small elevations in plasma sodium concentration (PNa) were effective in decreasing aldosterone secretion and, hence, in increasing sodium excretion in dogs fed normal sodium diets. Ten dogs fed a normal sodium diet, six DOCA-treated dogs, and four adrenalectomized dogs were given the same sodium load (2.5 mmol/kg) either as a hypertonic (1 M NaCl) or hypotonic (0.1 M NaCl) infusion. In all three groups of dogs, PNa was greater after the hypertonic than after the hypotonic infusion during most of the 22-h experiment. The dogs fed a normal sodium diet responded to the elevation in PNa (hypertonic infusion) with decreased aldosterone excretion and an exaggerated natriuresis. When aldosterone levels were maintained constant by either DOCA treatment or adrenalectomy, the exaggerated natriuresis that accompanied the hypertonic infusion was prevented. Therefore, elevation of PNa appears to be an important determinant of aldosterone secretion and, hence, of sodium excretion in conscious dogs fed normal sodium diets.
PCO2 measurements in surface proximal tubules and peritubular capillaries of the rat kidney
Authors: Gennari F. J. , Caflisch C. R. , Johns C. , Maddox D. A. , Cohen J. J.
Published: December 2017

PCO2 was measured in surface proximal tubules and peritubular capillaries in the rat under normal acid-base conditions and in three settings with decreased HCO3(-) reabsorption: benzolamide administration, respiratory alkalosis, and metabolic acidosis. Under normal conditions, PCO2 in the early proximal tubule (EP) was 10.5 mmHg higher than PaCO2 (P less than 0.001) and 3-4 mmHg higher than late proximal (LP) and peritubular capillary (PC) PCO2 (P less than 0.001). PCO2 in LP and PC was 7 mmHg higher than PaCO2 (P less than 0.001). Benzolamide (3 mg/kg) had no effect on the difference between PC and arterial PCO2 or between EP and PC PCO2. Increasing benzolamide to 8 mg/kg increased PCO2 in the surface structures relative to arterial PCO2 by 3-5 mmHg (P less than 0.01). Metabolic acidosis did not alter the relationships between cortical and arterial PCO2. By contrast, respiratory alkalosis decreased cortical PCO2 relative to PaCO2 by over 50%. Nonetheless, EP PCO2 was still higher than LP or PC PCO2 (P less than 0.01). Thus, reducing HCO3(-) reabsorption does not obliterate the difference between EP and LP or PC PCO2 nor does it invariably reduce PCO2 in the surface structures of the kidney relative to arterial PCO2.
Energetics of tubular sodium reabsorption sensitive to ethacrynic acid and ouabain
Authors: Sejersted O. M. , Steen P. A. , Kiil F.
Published: December 2017

Ouabain reduces renal oxygen consumption more extensively than ethacrynic acid despite similar natriuretic effects. Therefore, ethacrynic acid, which does not inhibit Na-K-ATPase, might stimulate energy metabolism unrelated to net sodium reabsorption. Experiments were performed on anesthetized dogs that had received isotonic saline intravenously corresponding to 10% of body wt and acetazolamide (100 mg.kg-1 i.v.). Subsequent infusion of ouabain in nine dogs (120 nmol.kg-1 intrarenally) reduced sodium reabsorption and oxygen consumption in parallel, giving a delta Na/delta O2 ratio of 18.0 +/- 1.1. With ethacrynic acid (3 mg.kg-1 i.v.) in six other dogs the delta Na/delta O2 ratio averaged 24.5 +/- 1.4. In a third group of five dogs, ouabain administered after ethacrynic acid reduced sodium reabsorption and oxygen consumption to the same levels as when ouabain was given alone. Thus, the high oxygen consumption remaining after ethacrynic acid can be inhibited by ouabain. We propose that ethacrynic acid generates a futile cycling of sodium by Na-K-ATPase across the basolateral cell membrane that is not apparent as net sodium reabsorption and is stopped by ouabain.U
Potential-dependent D-glucose uptake by renal brush border membrane vesicles in the absence of sodium
Authors: Hilden S. , Sacktor B.
Published: December 2017

The uptake of D-glucose by renal brush border membrane vesicles was studied in the absence of Na+. Uptake of the sugar was membrane potential dependent (inside negative), inhibited by phlorizin, sugar and stereospecific, accelerated by exchange diffusion, saturable, and temperature dependent. The binding of phlorizin in the absence of Na+ was also increased by a membrane potential (inside negative). Thus, the properties of this membrane potential-dependent, Na+-independent sugar transport system resembled those described for the Na+-D-glucose cotransport system. In the absence of Na+ but in the presence of a valinomycin-induced K+ diffusion potential the apparent Km for D-glucose was 43 mM. This contrasted with an apparent Km of 1.8 mM for the Na+ chemical gradient system. Therefore, the Na+-independent uptake system represented a low-affinity transport mechanism. It is suggested that the same carrier mediated the Na+-independent and Na+-dependent transport systems. A hypothetical model for the membrane potential-dependent stimulation of D-glucose uptake in the absence of Na+ is proposed.
Mechanism for the phosphaturia of NH4Cl: dependence on acidemia but not on diet PO4 or PTH
Authors: Guntupalli J. , Eby B. , Lau K.
Published: December 2017

The effects of metabolic acidosis on renal PO4 handling are controversial. Clearance experiments, therefore, were performed in fasted parathyroidectomized rats 1) to test the thesis that NH4Cl per se alters PO4 reabsorption, 2) to characterize the mechanisms responsible for these changes, and 3) to define the interaction of NH4Cl with parathyroid hormone (PTH) in PO4 deprivation. NH4Cl increased the clearance and fractional excretion of PO4 (FEPO4) without altering plasma PO4. Lactic acid and HCl, but not saline loading. NH4HCO3, or glutamine, produced similar effects. At steady-state phosphaturic effects of NH4Cl, neutralization of the acidemia by NaHCO3 abolished the increment. PTH (3.3 U.kg-1.h-1), superimposed on the maximal effective dose of NH4Cl (5.7 mmol.kg-1.h-1), further augmented FEPO4 (from 24.3 to 46.9%). The effects of NH4Cl (delta FEPO4 = 23 vs. 21%) and the synergism with PTH were not affected by PO4 deprivation. In both PO4 repletion and deprivation, NH4Cl increased basal and PTH-stimulated cAMP excretion, but the changes were poorly correlated with FEPO4. We conclude that NH4Cl inhibits PO4 reabsorption independent of PTH, extracellular fluid volume, natriuresis, NH4+ ion, plasma PO4, or the status of PO4 balance. The effects are mediated by mechanisms dependent on acidemia but are quite distinct from those of PTH. Our findings on cAMP are most compatible with the hypothesis that biochemical events beyond cAMP generation mediate both the phosphaturia of NH4Cl and its ability to restore PTH sensitivity in PO4 deprivation.
K, Cl, and H2O entry in endolymph, perilymph, and cerebrospinal fluid of the rat
Authors: Sterkers O. , Saumon G. , Tran Ba Huy P. , Amiel C.
Published: December 2017

The kinetics of radioactive potassium, chloride, and water entry into endolymph, perilymph, and cerebrospinal fluid were studied after intravenous administration of tracers in anesthetized and nephrectomized rats. Samples of cochlear endolymph, perilymph of scala vestibuli, perilymph of scala tympani, and cisternal cerebrospinal fluid were obtained. The data showed: 1) a rapid turnover of water in endolymph, perilymph, and cerebrospinal fluid, since 3H2O equilibrated with plasma in a few minutes; 2) a slow entry of 42K and 36Cl in perilymph, since 36Cl equilibrated with plasma after 2 h and 42K did not at 6 h; 3) an extremely slow entry of 42K and 36Cl in endolymph, since no equilibrium with plasma was obtained within the 5 h of the experiments. The comparison of the compartmental analysis of our data with the results of other studies using perilymphatic perfusion of tracers indicated that perilymph rather than plasma may be considered as the precursor of endolymph.
Increased Na+-H+ exchange in brush border vesicles from dogs with renal failure
Authors: Cohn D. E. , Hruska K. A. , Klahr S. , Hammerman M. R.
Published: December 2017

In the remnant kidney model of chronic renal failure, absolute reabsorption of Na+ in the proximal tubule of the remaining nephrons is increased over normal. Absolute proximal tubular reabsorption of bicarbonate and proximal tubular H+ excretion per nephron have also been shown to be increased over normal in his model of renal disease. Na+ uptake in membrane vesicles isolated from the brush border membrane of remnant kidneys of dogs with chronic renal failure is increased over uptake in membrane vesicles isolated from kidneys of normal dogs. In the present studies an amiloride-sensitive, electroneutral Na+-H+ exchanger was identified in canine renal brush border membrane vesicles. Na+ uptake in membrane vesicles in the presence of an initial H+ gradient (intravesicular pH less than extravesicular pH) was increased in membrane vesicles isolated from the remnant kidneys of dogs with chronic renal failure over that in membrane vesicles from kidneys of normal dogs. This increase was abolished by amiloride. It is possible that the alterations in Na+ and bicarbonate reabsorption and H+ excretion in the remnant kidney model of chronic renal failure can be explained on the basis of increased activity of the Na+-H+ exchanger in the renal brush border membrane.
Mechanism of altered glomerular hemodynamics during chronic sodium depletion
Authors: Tucker B. J. , Blantz R. C.
Published: December 2017

Chronic sodium depletion in the rat is associated with decreased nephron filtration rate (SNGFR), nephron plasma flow (rpf), and a reduction in the glomerular permeability coefficient (LpA). This study was designed to determine whether the reduction in LpA could be acutely reversed with volume repletion and whether administration of angiotensin I converting enzyme inhibitor will restore LpA to normal values in the sodium-depleted rat. Measurements were performed in Munich-Wistar rats employing micropuncture techniques to assess the effects of acute volume repletion, 3-5 days of oral converting enzyme inhibitor (CEI) (30 mg . kg body wt-1 . day-1), and longer term (13-18 days) treatment with CEI begun just before or after initial volume depletion. Volume repletion in chronic sodium-depleted rats restored LpA to normal control values within a 60-min period, and values for glomerular dynamics were not different from a group of normal NaCl-intake rats to which the same treatment was applied. Both short-term and long-term CEI treatment during sodium depletion resulted in restoration of rpf to values not different from those with normal NaCl intake. However, only long-term but not short-term CEI treatment restored LpA to normal values. These studies suggest that intrarenal angiotensin II may mediate this reduction in LpA during chronic sodium depletion, but an effect of adrenergic nerve activity has not been excluded.
Tubular capacity of phosphate transport in phosphate-deprived rats: effects of nicotinamide and PTH
Authors: Haramati A. , Knox F. G.
Published: December 2017

The present study tested the hypothesis that nicotinamide and/or parathyroid hormone (PTH) would reverse the resistance of phosphate-deprived rats to the phosphaturic effects of phosphate infusions by reducing the tubular capacity for phosphate transport. The response to progressively increasing rates of phosphate infusion (1, 2, and 3 mumol/min) was evaluated in thyroparathyroidectomized (TPTX) rats fed low phosphate diet (0.07%) for 4 days and treated with either vehicle or nicotinamide 2 h before the experiment. Following phosphate infusions, phosphate excretion was unchanged in vehicle-treated rats but increased progressively in nicotinamide-treated rats to 60% of the final rate of infusion. In a second series conducted in the presence of exogenous PTH, vehicle-treated rats responded to phosphate infusions by increasing phosphate excretion to 80-90% of the rate of infusion. In the presence of both nicotinamide and PTH, the rate of phosphate excretion matched the rate of infusion. Vehicle-treated rats displayed the highest reabsorptive rates without reaching a transport maximum, whereas a lower maximum reabsorptive rate was evident in nicotinamide-treated rats. However, in both groups given PTH, not only was the transport maximum lower but it declined with further increases in filtered load. We conclude that nicotinamide and PTH reverse the effects of dietary phosphate deprivation by decreasing the tubular capacity for phosphate transport.
Mechanism of diuresis following acute modest hyperglycemia in the rat
Authors: Blantz R. C. , Tucker B. J. , Gushwa L. , Peterson O. W.
Published: December 2017

In paired micropuncture studies in the Munich-Wistar rat we examined the mechanism of diuresis after acute induction of modest hyperglycemia (430-460 mg/dl) in the absence of an increase in total body water. The major reasons for the diuresis were an increase in nephron filtration rate (SNGFR) (from 30.3 +/- 1.8 to 35.3 +/- 1.6 nl/min) and a reduction in absolute proximal reabsorption (APR) (from 14.0 +/- 0.6 to 9.8 +/- 1.2 nl/min). All determinants of SNGFR were measured and a reduction in systemic oncotic pressure was the sole reason for the increase in SNGFR; vascular resistances did not change. Late proximal tubular fluid-to-plasma glucose concentration ratio was 0.96 +/- 0.04; therefore, the osmotic effects of unreabsorbed glucose could not account for the reduction in APR. Directly measured net renal interstitial pressure increased by 5 mmHg and the peritubular capillary effective reabsorptive pressure decreased (from 15.5 to 10.9 mmHg) in direct proportion to the reduction in APR, changes that could contribute to the reduction in APR. Equal elevations in glucose concentration in tubule and plasma may have also eliminated effective osmotic pressure gradients for water movement and influenced APR. As a result of increases in late proximal tubular flow rate, loop of Henle tubular reabsorption and absolute tubular reabsorption beyond the distal tubule both increased with hyperglycemia. The major reduction in APR was secondary to altered "physical factors" and osmotic effects of glucose that are not dependent on creation of unfavorable chemical gradients for Na+ reabsorption.
Sulfate transport by flounder renal tubule brush border: presence of anion exchange
Authors: Renfro J. L. , Pritchard J. B.
Published: December 2017

Transport of sulfate into brush border membrane (BBM) vesicles from renal tubules of southern flounder, Paralichthys lethostigma, was investigated. Imposition of a 21 mM HCO-3 gradient, in greater than out, produced concentrative sulfate uptake (overshoot) fourfold higher than equilibrium. Gradient conditions were necessary to produce this response; no overshoot was produced by the mere presence of HCO-3. Generation of potassium diffusion potentials with KCl gradients and valinomycin or short-circuiting of possible other ionic diffusion potentials had no effect on sulfate uptake. The rate-limiting step in HCO-3:SO2-4 exchange is, therefore, an electroneutral process. Although HCO-3 was the most effective counterion for sulfate, SCN-, Cl-, and S2O2-3 were also capable of promoting concentrative sulfate uptake. Sulfate uptake in the absence of counterion and bicarbonate-dependent sulfate uptake were both shown to be saturable processes. HCO-3-driven sulfate uptake could be inhibited by disulfonic stilbene, HgCl2, probenecid, chlorophenol red, and bromcresol green. Phloridzin, p-aminohippuric acid, 2,4-dinitrophenol, isethionic acid, and citric acid had no significant effect on HCO-3:SO2-4 exchange. The role of this sulfate:anion exchanger in active renal tubule sulfate secretion is discussed.
Prevention of ischemic acute renal failure with impermeant solutes
Authors: Burke T. J. , Arnold P. E. , Schrier R. W.
Published: December 2017

Studies were performed to evaluate the effect of solute permeability and extracellular osmolality in protecting against ischemic acute renal failure. The functional protective effect of a 1-min intrarenal perfusion (prior to intrarenal norepinephrine 0.75 micrograms . kg-1 . min-1) of a hypertonic permeant solute (hypertonic saline, 1,400 mosmol/kg H2O) and an isotonic impermeant solute (isotonic mannitol, 280 mosmol/kg H2O or isotonic polyethylene glycol, IPEG, 300 mosmol/kg H2O) was evaluated. Three hours after ischemia, the glomerular filtration rate was significantly lower in hypertonic saline group vs. either the isotonic mannitol- or IPEG-treated animals (2.4 vs. 8.9 and 10.4 ml/min, respectively; both P less than 0.05). Mean renal blood flow was similar in all three groups. The effects of hypertonic saline and IPEG on glomerular filtration pressure and tubular obstruction were also evaluated. Stop-flow pressure, as an index of glomerular filtration pressure, was higher in the IPEG- vs. the hypertonic saline-treated animals (40 vs. 35 mmHg, P less than 0.001). Although proximal tubular pressure was increased in both groups, transglomerular hydrostatic pressure was higher in the IPEG vs. the hypertonic saline group (13 vs. 6 mmHg, P less than 0.01). Tubular microperfusion studies demonstrated increases in proximal tubular pressure in the hypertonic saline but not the IPEG studies. The present results indicate that isotonic, impermeant solutes provide functional protection against ischemic acute renal failure. The beneficial effect of impermeant solute is mediated, at least in part, by better maintenance of transglomerular hydrostatic pressure and prevention of secondary tubular obstruction.
Renal hemodynamics in conscious rats: effects of anesthesia, surgery, and recovery
Authors: Walker L. A. , Buscemi-Bergin M. , Gellai M.
Published: December 2017

The influence of barbiturate anesthesia and minor surgical incisions on renal function was assessed in trained, chronically catheterized rats. In addition, renal hemodynamic changes during recovery from ether anesthesia and surgery were examined. Administration of pentobarbital in the chronic animals was associated with a marked reduction in arterial pressure (108 +/- 5 vs. 85 +/- 2 mmHg, P less than 0.01), renal blood flow (8.28 +/- 0.50 vs. 6.20 +/- 0.53 ml X min-1 X 100 g body wt-1, P less than 0.01), and glomerular filtration rate (1.30 +/- 0.10 vs. 0.97 +/- 0.11 ml X min-1 X 100 g body wt-1, P less than 0.01). Responses to Inactin were essentially identical. Small skin incisions during barbiturate anesthesia caused blood pressure to rise, but did not significantly change renal function parameters from already reduced values. In rats studied 2 h after ether anesthesia and surgical placement of catheters, arterial pressure was elevated compared with the same rats studied 4-7 days later (127 +/- 3 vs. 109 +/- 3 mmHg, P less than 0.005). Renal blood flow (5.80 +/- 0.37 vs. 8.90 +/- 0.93 ml X min-1 X 100 g body wt-1, P less than 0.01) and glomerular filtration rate (0.81 +/- 0.07 vs. 1.05 +/- 0.08 ml X min-1 X 100 g body wt-1, P less than 0.001) were markedly depressed during the recovery from surgery. It is concluded that barbiturate anesthesia depresses renal function in rats. This impairment should be considered when interpreting experiments that must be performed under anesthesia. In addition, the "conscious" preparation commonly used for renal studies in rats, i.e., one involving experimentation 2-3 h after ether anesthesia and surgery, is associated with a severe depression of renal hemodynamics.
Demonstration of an intrinsic renal adaptation for K+ conservation in short-term K+ depletion
Authors: Ornt D. B. , Tannen R. L.
Published: December 2017

Renal potassium conservation occurs within 3 days of potassium deprivation by a mechanism that appears to be independent of mineralocorticoids and sodium and anion excretion. To examine whether the mechanism involves an intrinsic renal adaptation, urinary potassium excretion was measured in isolated perfused kidneys from rats maintained on a normal or K+-free diet for 3 days. Perfusions were carried out with a K+ concentration that averaged 3.5 mM and with glucose (5 mM) as the only substrate. Both absolute (UKV) and fractional K+ excretion (FEK) were substantially less in kidneys from animals on K+-free diets compared with controls. These differences in K+ excretion were not explained by changes in GFR, urine flow rate, urine pH, or sodium, chloride, or ammonium excretion. The K+ content of renal tissue was not different in the perfused and nonperfused kidneys from rats receiving K+-free diets compared with controls. Suppression of K+ excretion by amiloride (10(-4) M) suggested that, as in vivo, tubular secretion of K+ in the perfused normal kidney accounts for 90% of the urinary K+ excretion and that tubular K+ secretion is reduced in isolated kidneys from animals on a K+-free diet. Further studies of isolated kidneys from adrenalectomized (ADX) rats receiving aldosterone and dexamethasone replacement and fed a normal or K-free diet also revealed significantly lower UKV and FEK in kidneys from animals on K+-free diets. K+ content of renal tissue was not different in the ADX animals on a K+-free diet compared with ADX rats on normal K+ intake. These studies indicate that within 72 h of dietary K+ deprivation an intrinsic renal adaptive process to conserve potassium is activated that is independent of renal potassium content, aldosterone, and urinary factors that can alter K+ excretion such as flow, pH, ammonium, sodium, and anions. This regulatory mechanism, which has a substantial influence on potassium excretion, remains to be elucidated.
Ammonium transport in rat cortical tubule: relationship to potassium metabolism
Authors: Jaeger P. , Karlmark B. , Giebisch G.
Published: December 2017

Free-flow micropuncture studies were carried out in rats to study the relationship between ammonium and potassium transport along superficial nephrons. Proximal and distal tubular fluid was analyzed for [3H]inulin, potassium, and ammonium. Ammonium was measured by a titrimetric formaldehyde method using a glass electrode to measure pH and an antimony electrode to deliver OH ions. In addition to experiments carried out under control conditions, the rats were also acutely potassium loaded, chronically potassium depleted, or given glutamine intravenously to stimulate ammonium excretion. Ammonium production along the proximal tubule was sharply enhanced in potassium depletion and, most likely, also following glutamine infusion, but it remained unchanged during hyperkalemia. Significant amounts of ammonium were lost along the loop of Henle in all experimental conditions. During stimulation of ammonium excretion by either potassium depletion or glutamine infusion the urine became alkaline. No loss or gain of ammonium beyond the late distal tubule was observed in any of the experimental conditions. With respect to potassium transport the glutamine-induced rise in urinary ammonium excretion was associated with stimulation of potassium reabsorption beyond the late distal tubule.
Influence of acute potassium loading on renal phosphate transport in the rat kidney
Authors: Jaeger P. , Bonjour J. P. , Karlmark B. , Stanton B. , Kirk R. G. , Duplinsky T. , Giebisch G.
Published: December 2017

This study examined 1) whether potassium-induced depression of phosphate excretion is a parathyroid hormone-dependent phenomenon, and 2) whether such stimulation of tubular phosphate reabsorption capacity involves increased phosphate reabsorption in the distal tubule. Potassium was infused into intact rats (25 mumol X min-1 X kg-1) during stepwise addition of phosphate to the infusion and led to a significant drop in phosphate excretion; this effect was abolished in thyroparathyroidectomized (TPTX) animals. In intact rats the maximal tubular Pi reabsorption per milliliter of glomerular filtrate (max TRPi/ml GF) was significantly higher in the potassium group (2.54 +/- 0.06 mumol/ml GF) compared with the control group (2.31 +/- 0.06 mumol/ml GF) (means +/- SE). In TPTX rats no difference in max TRPi/ml GF was observed: 3.44 +/- 0.07 and 3.49 +/- 0.07 mumol/ml GF during potassium and sodium infusion, respectively. Free-flow micropuncture was carried out on superficial distal tubules of intact rats and fluid samples were analyzed for [3H]inulin and phosphorus (electron microprobe). Phosphorus delivery into the distal tubule was similar in control and potassium-loaded rats. Whereas net phosphorus reabsorption along the distal tubule was absent in the control group, intravenous potassium administration stimulated distal phosphorus reabsorption. Conclusion: potassium stimulates renal phosphate reabsorption capacity, an effect that is abolished after TPTX. The potassium effect on phosphate occurs along the distal tubule.
Mechanisms of active H+ secretion in the proximal tubule
Authors: Aronson P. S.
Published: December 2017

This Editorial Review describes the mechanisms that have been identified for mediating active H + secretion across the luminal membrane of the proximal tubular cell. These include Na+-H+ exchange, Na+-phosphate cotransport, organic anion-OH- exchange, ATP-driven H+ transport, and redox-driven H+ transport. Of these, Na+-H+ exchange appears to bethe most important. Indeed, there is no conclusive evidence against the concept that luminal membrane Na+-H- exchange is the principal if not the sole mechanism for mediating active H+ secretion in the proximal tubule. The transport properties of the Na+-H+ exchanger, particularly its striking sensitivity to intracellular pH, can explain many aspects of howthe rate of active H+ secretion in the proximal tubule is regulated in response to various physiologic stimuli. Certainly, important physiologic roles for other H+ secretory mechanisms, especially those involving primary active H+ secretion,have not been excluded. Nevertheless, there is not yet definitive proof that ATP-driven or redox-driven H+ pumps are located on the luminal membrane itself or that they significantly contribute to transtubular H+ secretion.
Cellular response to acute respiratory acidosis in rat medullary collecting duct
Authors: Madsen K. M. , Tisher C. C.
Published: December 2017

The collecting duct of the mammalian kidney is involved in urine acidification. Recent studies in the turtle bladder suggest that hydrogen ion secretion in response to elevated CO2 is regulated by insertion of hydrogen pumps into the luminal membrane of the mitochondria-rich cells. Because intercalated cells of the collecting duct are structurally similar to mitochondria-rich cells of the amphibian bladder, we studied the rat outer medullary collecting duct (OMCD) during respiratory acidosis to determine whether changes compatible with hydrogen ion secretion occur in the intercalated cells. Rats were studied during normal acid-base conditions and after 4-5 h of respiratory acidosis. After collection of physiologic data, the kidneys were fixed by in vivo perfusion and processed for electron microscopy. No changes were observed in the principal cells of the OMCD. Morphometric analysis revealed a significant increase in the surface density of the apical plasma membrane and a decrease in the number of tubulovesicular profiles in the apical region of the intercalated cells throughout the OMCD with respiratory acidosis. There were no changes in surface density of the basolateral membrane. These findings suggest that in response to respiratory acidosis there is transport of membrane from the tubulovesicular membrane compartment to the apical plasma membrane of the intercalated cells.
Modification of carboxyl of Na+ channel inhibits aldosterone action on Na+ transport
Authors: Kipnowski J. , Park C. S. , Fanestil D. D.
Published: December 2017

We investigated the effect of the carboxyl-selective reagent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) on aldosterone stimulation of Na+ transport in the urinary bladder of the toad. Na+ transport, measured as the short-circuit current (SCC), was irreversibly inhibited by EEDQ in a dose- and time-dependent manner prior to addition of aldosterone. The greater the percentage inhibition by EEDQ (X), the smaller was the maximal increase of SCC after aldosterone (Y). This relationship gave the regression equation Y = 128.41 - 1.73X, r = -0.99 (n = 35). Evidence that the inhibition of SCC produced by EEDQ was limited to effects at the mucosal membrane was attested by the following: 1) EEDQ did not alter the stimulation by aldosterone of the osmotic water flow response to antidiuretic hormone; 2) whereas inhibition of protein synthesis by cycloheximide prevented this effect of aldosterone; 3) amphotericin B fully restored SCC previously inhibited by EEDQ to the level produced in tissues not inhibited by EEDQ; 4) comparison of the effects of amiloride vs. EEDQ pretreatment on the SCC response to aldosterone and amphotericin B revealed nearly identical characteristics; 5) in contrast, amphotericin B stimulation of SCC was limited when Na+ transport was limited by antimycin A (an inhibitor of energy production) or by ouabain. The findings fail to provide positive evidence for the hypothesis that aldosterone induces the synthesis of new Na+ channels but are consistent with hormonal activation of previously existing but nonfunctioning Na+ channels.
Localization of tissue potassium pools in the amphibian kidney
Authors: Wilkinson H. L. , Sullivan L. P. , Welling D. J. , Welling L. W.
Published: December 2017

Techniques were developed to determine the location of exchangeable K pools that had been identified previously in kinetic studies of the intact perfused bullfrog kidney. Following perfusion of the kidneys with 42K, a washout of the isotope was begun and interrupted at various times; the kidneys were removed, frozen, dried at low pressure and temperature, and then microdissected. Glomerular capillary tufts, small segments of tissue containing early distal tubules (diluting segment), and other segments containing proximal tubular convolutions were removed and analyzed for total content of K and 42K. In the intact kidney 77% of tissue K exchanged in 60 min. The exchangeable K concentration was 95 mu eq/ml cell water. Correction for the K activity coefficient in Ringer solution yielded an activity of 72 mu eq/ml. Thirty-two percent of glomerular capillary K exchanged in 60 min; 7% exchanged with a half time of 3.5 min; and the remainder exchanged at a rate too slow to measure. The data from tissue containing proximal tubular segments were too scattered to permit analysis. In segments containing early distal tubules, 67% of tissue K was contained in two exchangeable pools: one pool exchanged at a rate 10-fold greater than did the other. The data for these two distal pools were analyzed in terms of a parallel model (two cell types?) and a nested model (cytoplasm and subcellular organelles?). Pool size and exchange rates were calculated for both models. Electron microscopic analysis revealed that early distal tubular segments contain only one cell type which has a large population of mitochondria. This suggests that the nested model is more plausible. The fast distal pool exchanged at the same rate as the fast-exchanging pool identified in kinetic studies of the intact functioning kidney and is considered to be the K secretory pool.
Localization of the cerebroventricular receptors involved in CNS-induced natriuresis
Authors: Pierce E. T. , Mouw D. R.
Published: December 2017

Ventriculocisternal perfusion (VCP) or localized “push-pull” perfusion (PPP) was performed in pentobarbital-anesthetized dogs. Renal function was studied in protocols consisting of a 1-h experimental period bracketed by 1-h control and recovery periods. The animals were perfused with artificial cerebral spinal fluid (CSF) throughout the protocol but the sodium concentration was elevated (300 mM, high Na) during the experimental period. In the first series of experiments, prior to VCP, petroleum jelly plugs were injected into either the ventral third ventricle (V3V) or other brain regions. When petroleum jelly plugs were injected into the V3V prior to VCP, they prevented perfusates from reaching this area, as determined by subsequent dye perfusion. These V3V plugs blocked the natriuresis and ADH response otherwise induced by high Na VCP. In the second series of experiments, the anterior portion of the V3V (AV3V) was perfused by means of PPP. In some of the PPP experiments a V3V plug was also injected to ensure restriction of the stimulus to the AV3V. PPP of the AV3V with high Na CSF at 50 microliter/min did not induce a natriuresis (either with or without a V3V plug). However, when the high Na CSF was perfused at a very high rate (100 microliter/min) and the stimulus was not restricted to the AV3V by a V3V plug, a natriuresis did occur. These results suggest that the ventricular surface where high Na CSF acts to cause natriuresis and increased ADH secretion is within the V3V region but not in the AV3V.
Renal gluconeogenesis: axial and internephron heterogeneity and the effect of parathyroid hormone
Authors: Wang M. S. , Kurokawa K.
Published: December 2017

To better understand the regulation of renal gluconeogenesis that occurs in the proximal nephron, glucose production rates from various substrates were determined in defined proximal tubule segments of the rat. Tubule segments tested were the S1 and S2 segments of superficial (SF) nephrons, the S1 segments of juxtamedullary (JM) nephrons, and the S3 segments. Glucose production (in decreasing order) was: from alpha-ketoglutarate, JM S1, SF S1, SF S2; from pyruvate, SF S2, JM S1, and SF S1; from glutamine, SF S1, JM S1; and from glutamate, SF S1 = JM S1. Little glucose was produced in the S3 segments. Glucose production from glutamate was lower than that from the other three substrates in JM S1, and glutamine was the best gluconeogenic substrate in SF S1. The effects of parathyroid hormone (PTH), a known stimulator of renal gluconeogenesis, and cAMP were examined using alpha-ketoglutarate as the substrate. Both stimulated glucose production in the S1 and S2 segments of the SF nephron. Although PTH stimulated adenylate cyclase in the S1 segments of the SF and JM nephrons, it had no effect on glucose production in the JM S1. Glucose production rose in the SF S1 and JM S1 in response to increasing concentrations of hydrogen or calcium ions, indicating that gluconeogenesis can be increased in these nephron segments. Differences may therefore be present in the cellular responses to PTH distal to cAMP formation in the nephron segments of the SF and JM nephrons. These findings show the presence of both axial and internephron heterogeneity of renal gluconeogenesis and suggest the difference in the effects of PTH on the function of SF and JM nephrons.
Renal nerves and cation excretion after acute reduction in functioning renal mass in the rat
Authors: Ribstein J. , Humphreys M. H.
Published: December 2017

We evaluated the role of the renal nerves in the increased cation excretion by the contralateral kidney after acute unilateral nephrectomy (AUN) or unilateral ureteral occlusion (UUO) in anesthetized rats. Both AUN and UUO caused large increases in sodium (UNaV) and potassium excretion (UKV) by the control kidney without change in glomerular filtration rate or mean arterial pressure. Prior denervation of either the ipsilateral (experimental) kidney or the control kidney completely prevented the increase in UNaV and UKV after UUO. Prior denervation of either kidney also prevented the increase in UNaV after AUN. However, a significant kaliuresis persisted after AUN despite unilateral denervation although reduced in magnitude when compared with the increase in UKV after AUN with both kidneys innervated. These results indicate that the renal nerves play a major role in the excretory response of the control kidney after acute reduction in functioning renal mass. This role of the renal nerves may be through the activation of a renorenal reflex. The reflex is activated by afferents from the ipsilateral kidney; the efferent limb is composed of the renal nerves to the control kidney. This reflex can entirely account for the compensatory increase in cation excretion after UUO. However, a separate mechanism, not dependent on the renal nerves, contributes to UKV after AUN.
Effect of pH on glutamate efflux from rat kidney mitochondria
Authors: Schoolwerth A. C. , LaNoue K. F. , Hoover W. J.
Published: December 2017

To provide further insight into the relationship between glutamate transport and metabolism in rat kidney mitochondria, the effect of pH on [U-14C]-glutamate efflux from [U-14C]glutamate-loaded mitochondria was tested. Glutamate efflux, measured in rotenone-inhibited energized mitochondria at 28 degrees C, was first order with respect to matrix glutamate. Glutamate efflux was tested at different medium pH values ranging from 6.4 to 7.9. Efflux was fastest at pH 7.9 with a rate constant of 0.988 min-1 and decreased progressively at lower pH values such that the rate constant at pH 6.4 was 0.359 min-1. A highly significant correlation between pH and the rate constant of glutamate efflux was observed. When medium pH was held constant at 7.0, matrix pH (range pH 7.2-8.4) did not affect the rate of glutamate efflux. The reduction in glutamate efflux at low pH provides an explanation for the increased concentration of glutamate observed in the mitochondrial matrix space of isolated rat kidney mitochondria incubated at acid medium pH. The elevated glutamate concentration in turn contributes to the accelerated oxidative deamination of glutamate by glutamate dehydrogenase at acid pH. Moreover, these findings suggest that the reduction in renal cortex glutamate levels observed in acute acidosis in vivo may be explained by a decreased rate of glutamate transport from mitochondria to cytosol coupled with an augmented rate of glutamate oxidation in the matrix.
Phosphate transport in the proximal convoluted tubule: effect of intraluminal pH
Authors: Quamme G. A. , Wong N. L.
Published: December 2017

The effect of intraluminal hydrogen ion concentration on phosphate absorption was evaluated in the rat superficial proximal tubule. Early proximal convoluted tubules were perfused in vivo with buffered equilibrium solutions, and the saturation kinetics for phosphate transport was determined by altering intraluminal phosphate concentration at pH values of 7.65 and 6.5. The apparent Jmax and Km parameters of phosphate transport were about twofold greater with intraluminal pH 7.65 compared with pH 6.5 values. Accordingly, intraluminal hydrogen ion had a direct effect on tubular phosphate transport. Endogenous or exogenously administered parathyroid hormone inhibited phosphate absorption at both pH values, indicating that the phosphaturic action of parathyroid hormone is independent of the intraluminal pH value. Elevation of plasma phosphate inhibited phosphate absorption unrelated to the intraluminal phosphate concentration at both pH values. These data suggest that elevation of plasma phosphate may decrease phosphate absorption by inhibiting efflux from the cell into the peritubular capillary. In conclusion, proximal phosphate absorption is determined by the intraluminal pH value, circulating parathyroid hormone level, and plasma phosphate concentration acting through separate cellular and membrane mechanisms.