bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of metabolic acidosis on PTH and 1,25(OH)2D3 response to low calcium diet
Authors: Bushinsky D. A. , Favus M. J. , Schneider A. B. , Sen P. K. , Sherwood L. M. , Coe F. L.
Published: December 2017

To study the effects of chronic metabolic acidosis on the metabolism of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] rats were given either a low calcium diet (LCD) (0.002% calcium) or chow (1.2% calcium); ammonium chloride (NH4Cl) was added (1 or 1.5%) to the drinking water of some rats eating LCD or chow while others served as nonacidotic controls. LCD increased circulating 1,25(OH)2D3 levels from 46 +/- 14 to 204 +/- 24 pg/ml (P less than 0.001) in the absence of NH4Cl; 1.5% NH4Cl prevented the increase in 1,25(OH)2D3 (25 +/- 6 vs. 27 +/- 8 pg/ml (P, NS) but 1% NH4Cl did not (50 +/- 12 vs. 161 +/- 23 pg/ml; P less than 0.001). Acidosis suppressed neither serum immunoreactive parathyroid hormone (PTH) nor urine cAMP response to LCD. Although total serum calcium and phosphorus showed no regular changes with NH4Cl, acidosis raised blood ionized calcium in rats fed either chow or LCD, and serum 1,25(OH)2D3 levels were inversely correlated with ionized calcium (r = 0.714; P less than 0.001) during LCD. Chronic NH4Cl acidosis prevented serum 1,25(OH)2D3 from rising during LCD, independent of changes in PTH secretion, cAMP generation, or serum phosphorus. The absence of a 1,25(OH)2D3 response may be due to increased ionized calcium produced by acidosis.
Tubular reabsorptive capacity for magnesium in the dog kidney
Authors: Wong N. L. , Dirks J. H. , Quamme G. A.
Published: December 2017

Micropuncture studies were performed on 27 thyroparathyroidectomized dogs to determine the segmental reabsorption of magnesium before and after graded magnesium infusion. Overall kidney reabsorption, as determined by the difference between filtered magnesium and urinary excretion, initially increased with elevation of plasma magnesium up to 3.5 meq/liter. Further elevation of plasma magnesium resulted in the appearance in the urine of all additional increments in filtered magnesium. Thus, renal magnesium reabsorption followed a pattern characteristic of a maximal transport rate (Tm). Evaluation of the proximal tubule by micropuncture demonstrated that net reabsorption of magnesium rose proportional to the increase in filtered magnesium and accounted for a constant fractional reabsorption of 14%. In contrast, magnesium reabsorption in Henle's loop initially increased with low delivery rates but peaked and fell with high plasma magnesium concentrations. Little magnesium reabsorption was observed between the distal collection site and final urine. Accordingly, the overall urinary excretion pattern was a summation of the different effects occurring in the proximal tubule and Henle's loop. Thus, renal magnesium reabsorption is not characterized by a Tm process but is a composite of distinct transport properties of the proximal tubule and the loop of Henle.
Antidiuretic hormone-dependent membrane capacitance and water permeability in the toad urinary bladder
Authors: Palmer L. G. , Lorenzen M.
Published: December 2017

Antidiuretic hormone (ADH) increased the electrical capacitance of apical membrane of the toad bladder; this effect was modulated by the osmotic gradient across the tissue. Capacitance was measured from the transepithelial voltage response to constant-current pulses using bladders depolarized with KCl-sucrose serosal solution to reduce basolateral resistance and with Na-free mucosal solution to increase apical membrane resistance. Addition of ADH (20 mU/ml) increased capacitance by 28 +/- 9% (mean +/- SD) in the absence and by 8 +/- 3% in the presence of an osmotic gradient (200 mosM, mucosal side hypotonic). With bladders stimulated in the absence of an osmotic gradient, rapidly imposing a gradient resulted in a peak rate of water flow that declined to 40% of the peak value after 15-20 min. ADH-dependent capacitance also decreased with a similar time course. Removal of ADH reversed the capacitance change (t1/2 = 10-15 min), but the reversal was slower than the decline in water flow to basal levels (t1/2 less than 5 min). Colchicine and cytochalasin B also inhibited the ADH-induced capacitance increase. The capacitance change was also inhibited when the mucosal solution was made hypertonic with raffinose. The results are interpreted within the framework of a previously proposed model of ADH-stimulated water transport in which cytoplasmic vesicular structures fuse with the apical plasma membrane.
Mechanism of cold diuresis in the rat
Authors: Morgan M. L. , Anderson R. J. , Ellis M. A. , Berl T.
Published: December 2017

The effect of cold exposure (CE) on renal water excretion has not been clearly delineated. Conscious rats were exposed to decreased ambient temperature (15 degrees C). Forty-five minutes of CE resulted in reversible increases in urine flow and decreases in urine osmolality. The diuresis was not due to a diminished response to vasopressin (VP), as the antidiuresis associated with 500 microU of Pitressin given to water-diuresing rats was comparable at 15 and 30 degrees C. To determine whether the diuresis was due to intrarenal factors, glomerular filtration rate, renal blood flow, sodium excretion, and osmolar clearances were measured and found to be equivalent during control and cold conditions. To determine whether the observed diuresis was due to suppression of endogenous VP, VP-free Brattleboro rats undergoing a constant VP infusion were cold exposed. In these rats, CE was not associated with a change in either urine flow or urinary osmolality. This antidiuretic hormone-mediated mechanism was corroborated by a decrease in immunoassayable VP levels. To determine the mechanism whereby CE suppresses endogenous VP, plasma osmolality and hemodynamic parameters were measured. Although CE was not associated with a change in plasma osmolality, it did result in a significant increase in both mean arterial pressure and cardiac index. Pretreatment of rats with 6-hydroxydopamine prevented both the increase in mean arterial pressure and cold diuresis. We conclude that the diuresis observed upon exposure to 15 degrees C results from nonosmotic suppression of endogenous VP, as a consequence of the increase in mean arterial pressure.
Effects of prostacyclin on short-circuit current and water flow in the toad urinary bladder
Authors: Pohlman T. , Yates J. , Needleman P. , Klahr S.
Published: December 2017

The effects of prostaglandins of the E series on sodium and water transport have been studied extensively. PGE2 has been shown to inhibit the increase in osmotic water flow produced by vasopressin and to stimulate short-circuit current (SCC) in the toad bladder. On the other hand, the effects of prostacyclin (PGI2), an arachidonic acid product, on sodium and water transport have not been extensively evaluated. The present studies describe the effects of PGI2 on basal and vasopressin-stimulated osmotic water flow and on SCC in the urinary bladder of the toad. Studies were performed in the absence or presence of indomethacin. PGI2 in the absence of indomethacin had no effect on basal or vasopressin-stimulated osmotic water flow. When indomethacin was present, thereby eliminating intrinsic prostaglandin biosynthesis, PGI2 inhibited basal but not vasopressin-stimulated osmotic water flow. PGI2 increased SCC in the presence or absence of indomethacin. 6-keto PGF1 alpha, the stable metabolite of PGI2, had no effect on SCC. PGI2 stimulated cAMP production in isolated toad bladder epithelial cells. 2',5'-Dideoxyadenosine, an inhibitor of cAMP production, blocked the increase in SCC produced by PGI2, suggesting that the effects of this compound on SCC are mediated via cAMP.
Glucagon degradation by luminal and basolateral rabbit tubular membranes
Authors: Talor Z. , Emmanouel D. S. , Katz A. I.
Published: December 2017

Glucagon is avidly degraded by the kidney, but the relative contribution of the luminal and basolateral tubular membranes to this process is unknown. We studied 125I-glucagon degradation by purified luminal (L) and basolateral (BL) tubular membranes prepared from rabbit kidney cortex, which showed enrichment vs. homogenate of marker enzyme activities (Na-K-ATPase for BL and maltase for L) of 10- and 14-fold, respectively. Renal homogenates and both tubular membrane fractions degraded glucagon avidly without reaching saturation even at pharmacologic concentration (10(-5) M) of the hormone. At physiologic concentration (3 x 10(-11) M) BL membranes degraded substantial amounts of glucagon (8.1 +/- 0.9 pg . micrograms protein-1 . h-1) even though at lesser rates (P less than 0.001) than the luminal fraction (33.3 +/- 1.9 pg . micrograms protein-1 . h-1). Competition experiments suggested that glucagon-degrading activity in both fractions includes both specific and nonspecific components, and the potency of different enzyme inhibitors to decelerate glucagon degradation was strikingly similar in the two membrane preparations. Glucagon degradation differed in several important aspects from the manner in which tubular membranes catabolize insulin, including absolute degradation rates and relative degrading capacity of the membranes vs. homogenates, both being substantially higher for glucagon. These results provide direct evidence that the renal metabolism of glucagon also involves its degradation by peritubular cell membranes.
Effect of potassium on renal NH3 production
Authors: Sastrasinh S. , Tannen R. L.
Published: December 2017

The influence on renal ammoniagenesis of a high potassium diet and also of acute manipulation of ambient potassium concentration was investigated using both the isolated perfused rat kidney and incubated renal cortical tubules. Ingestion of a high potassium diet for 1 wk resulted in potassium adaptation but had no effect on ammonia production by the isolated kidney perfused with physiologic concentrations of glutamine. By contrast, perfusion with a high ambient potassium concentration (8.0-9.3 mM) significantly increased renal tissue potassium levels and concomitantly reduced the rate of ammonia formation by 30% in comparison with perfusions at a normal potassium concentration. NH3 production by tubules incubated with 1 mM glutamine was also decreased at a K+ concentration of 9.0 mM. Ammonia production was unchanged when kidneys were perfused with a potassium concentration of 2.0 mM despite a 16% decrease in renal tissue potassium levels, but ammonia production by tubules incubated in 2 mM K+ was slightly less than in control incubations at 5.0 mM. Thus, unlike earlier in vitro studies with outer medullary slices, these studies do not support the hypothesis that an adaptive change in ammoniagenesis results from a high dietary potassium intake. However, a high ambient and renal intracellular potassium concentration can depress ammonia production. Although potassium depletion causes an adaptive increase in ammonia production, a decrease in ambient potassium concentration does not increase ammoniagenesis. Accordingly, both a potassium surfeit and deficit can modify renal ammonia production, but the mechanisms involved appear to differ.
Pressure effects on the ADH-induced initiation of water flow in toad bladder
Authors: Coluccio L. M. , Brady R. J. , Parsons R. H.
Published: December 2017

Earlier studies employed colchicine to demonstrate the need for microtubules in the ADH-induced initiation of increased water permeability in toad bladder. We have used colchicine and hydrostatic pressure together to determine whether formed or growing microtubules are required for initiation of the ADH response in Bufo marinus. When ADH and 8,000 psi were administered simultaneously, the ADH-induced increase in water flow was inhibited while under pressure by 107 +/- 7% (n = 6). Application of 8,000 psi for 10 min before ADH administration resulted in an increased initiation of the ADH osmotic response over the non-pressure-treated control (average acceleration, rate of water flow increase during first 3 min after ADH stimulation, 1.25 +/- 0.27 vs. 0.43 +/- 0.12 mg X cm-2 X min-2, n = 6). In addition, the inhibition of the ADH response brought about by colchicine incubation was overcome with pretreatment of the colchicine-incubated bladders with 8,000 psi for 10 min (average 3-min acceleration, 0.18 +/- 0.04 vs. 1.13 +/- 0.06 mg X cm-2 X min-2, respectively). Repeating the experiments with dibutyryl cAMP gave similar results. We interpret these data as suggesting that growing microtubules are required for initiation. The proposed model is as follows. Pressure removes colchicine inhibition by introducing, through disassembly of formed microtubules, more colchicine-free tubulin subunits. These subunits are then available following decompression to reassemble when the tissue is challenged with hormone.
Freeze-dissection analysis of 133Xe distribution to measure regional renal blood flow
Authors: Passmore J. C. , Allen R. L. , Hock C. E. , Neiberger R. E.
Published: December 2017

To verify the freeze-dissection technique for measuring renal blood flow (RBF) distribution in anesthetized dogs we compared the sum of all compartment flow rates with total RBF, compared compartment flow distribution with intercepts, and determined recirculated 133Xe. By dissection, we found that the cortex, delineated by its granular brownish red appearance, comprised 69%, whereas the outer medulla (the reddish portion) was 18% of the total kidney weight. Average cortical flow was 3.77 ml X g-1 X min-1 and the y-intercept for 133Xe washout was 85% of the initial radioactivity distribution. Outer medullary flow was 2.01 ml X g-1 X min-1 with a y-intercept of 13%. In a 100-g kidney, total cortical flow would be 259.8 ml/min (3.77 ml X g-1 X min-1 X 68.9 g) and total outer medullary flow would be 36.0 ml/min. These calculations indicate that 86% of the total flow is distributed to the cortex and 13% to the outer medulla, as the intercept-calculated percentages indicated. Summing whole cortical and medullary flows results in a flow that agrees with the electromagnetically measured flow of 292 ml/min for a 100-g kidney.
Effect of acute potassium infusion on loop segment chloride reabsorption in the rat
Authors: Kirchner K. A.
Published: December 2017

To assess the effect of acute potassium loading on proximal tubule and loop chloride handling, chloride transport was examined in superficial cortical nephrons in control rats and after infusion with either 0.3 M KNO3 (KVE) or 0.3 M NaNO3 (NaVE) using micropuncture techniques. Infusion with either salt increased plasma volume, single nephron glomerular filtration rate (SNGFR), and delivery of fluid and chloride out of the proximal tubule. Plasma volume, tubule fluid-to-plasma inulin ratio, proximal transepithelial chloride ratio, and absolute and fractional proximal chloride delivery, however, were not different in the NaVE and KVE groups. Early distal tubule fluid flow rate, SNGFR, and fluid reabsorption were greater than control values following either infusion but these were not different between KVE and NaVE. Early distal tubule chloride concentration and transepithelial chloride gradient were greater and fractional chloride reabsorption was less in KVE than in either control or NaVE groups. Calculated fractional loop segment chloride reabsorption was less in KVE animals. These data suggest that potassium loading reduces fractional chloride reabsorption in the loop segment of rat superficial cortical nephrons.
Furosemide action on collecting ducts: effect of prostaglandin synthesis inhibition
Authors: Wilson D. R. , Honrath U. , Sonnenberg H.
Published: December 2017

The effect of furosemide on inner medullary collecting duct chloride reabsorption has not been determined, and the blunting of furosemide action by drugs that inhibit prostaglandin synthesis, while known to occur, has not been examined in detail. The effect of indomethacin and meclofenamate on furosemide diuresis was studied in the rat using clearance and collecting duct microcatheterization methods. Furosemide-treated control animals showed complete inhibition of chloride, sodium, and water reabsorption in the inner medullary collecting duct. Rats given indomethacin or meclofenamate before and during furosemide administration showed marked reduction of the chloriuresis, natriuresis, and diuresis. Reduced delivery of sodium and chloride to the beginning of the inner medullary collecting duct, associated with a decrease in glomerular filtration rate and increased reabsorption in more proximal nephron segments, was largely responsible for the reduced natriuresis and chloriuresis during inhibition of prostaglandin synthesis. In addition, indomethacin increased collecting duct NaCl reabsorption toward normal, but meclofenamate showed no such effect. The results indicate that furosemide inhibits medullary collecting duct reabsorption of chloride, sodium, and water in the rat. The blunting of diuretic action seen with inhibition of prostaglandin synthesis is largely, although not entirely, due to effects of indomethacin and meclofenamate on furosemide action at nephron sites proximal to the collecting duct.
Angiotensin in the hemodynamic response to chronic nephron obstruction
Authors: Carmines P. K. , Tanner G. A.
Published: December 2017

Microsphere techniques were employed to investigate the role of intrarenal angiotensin generation in producing the arteriolar constriction associated with 24-h tubular obstruction in rats. In each animal, glomerular blood flow (GBF) and nephron vascular resistance were determined for normal and oil-blocked superficial cortical nephrons. In 17 control rats, GBF of normal and blocked nephrons averaged 226 +/- 12 and 130 +/- 9 nl/min, respectively (P less than 0.001). Captopril treatment in five rats (10 mg/kg orally) improved GBF to blocked nephrons to 252 +/- 31 nl/min. Saralasin treatment in six rats (10 micrograms . kg-1 . min-1 i.v.) lessened the difference between GBF of normal and obstructed nephrons. In six rats subjected to a high salt intake and deoxycorticosterone injections, GBF to obstructed nephrons was improved to 181 +/- 21 nl/min. Since both pharmacologic interruption of angiotensin activity and renin suppression were associated with improved GBF of blocked nephrons, these observations support a role for angiotensin as a local factor controlling glomerular hemodynamics of chronically obstructed nephrons.
Mechanism of urate and p-aminohippurate transport in rat renal microvillus membrane vesicles
Authors: Kahn A. M. , Branham S. , Weinman E. J.
Published: December 2017

The transport of urate and p-aminohippurate (PAH) was evaluated in brush border membrane vesicles from the rat renal cortex. The binding of urate to the membranes was 6% of total uptake and no conversion of urate to allantoin was detected. The binding of PAH to the membranes was 24% of total uptake. In the presence of an outwardly directed hydroxyl ion gradient (pHi = 7.5, pHo = 6.0), the uptake of urate and PAH was stimulated relative to the absence of a hydroxyl ion gradient (pHi = pHo = 7.5) and the influx of urate resulted in a transient overshoot of the equilibrium value. The hydroxyl ion gradient-stimulated uptake of urate and PAH was not solely due to a change in membrane potential. Probenecid, DIDS, furosemide, and pyrazinoate inhibited the hydroxyl ion gradient-stimulated uptake of urate and PAH in a dose-dependent manner. The uptake of [14C]urate and [3H]PAH could be cis-inhibited and trans-stimulated by either unlabeled urate or PAH. In the presence of an outwardly directed bicarbonate gradient and 10% CO2 (outside HCO-3 = 5.4 mM, inside HCO-3 = 54 mM, pHo = 6.5, pHi = 7.5), the initial rate of urate uptake was faster and the initial rate of urate efflux was slower compared with vesicles that had the same pH gradient without bicarbonate or CO2. The effects of bicarbonate gradients on organic anion transport were not dependent on diffusion potentials. Finally, 100 mM extravesicular Na+, K+, Li+, or Cs+ did not affect urate or PAH uptake. These results indicate that brush border membrane vesicles from the rat kidney contain an anion exchange transport system with affinity for urate, PAH, hydroxyl ions, and bicarbonate. In addition there is no evidence for a sodium-urate or sodium-PAH cotransport mechanism in these membranes.
Renal adaptation to alteration in dietary amino acid intake
Authors: Friedman A. L. , Albright P. W. , Gusowski N. , Padilla M. , Chesney R. W.
Published: December 2017

The nonessential beta-amino acid taurine, which is inert in renal tissue, was used to study the renal adaptation to dietary taurine change. Three isoproteinic diets were employed: HTD--high in taurine, NTD--normal taurine, and LTD--deficient in the taurine precursors cysteine and methionine. When compared with NTD, HTD resulted in an increase in the urinary excretion and fractional excretion of taurine, whereas LTD led to a decrease in urinary excretion and fractional excretion of taurine. In vitro studies demonstrated an increase in the Vmax of the high-affinity, low-capacity uptake system with no change in "apparent" Km following LTD. Complete adaptation developed within days after the diet was changed (NTD to HTD = 3 days; NTD to LTD = 3-6 days). These studies demonstrate that the renal response to altered dietary amino acid can be evaluated and that adaptation occurs for the beta-amino acid taurine. The renal response serves to conserve taurine during periods of deprivation and to dispose of taurine during periods of excess. The renal adaptation to restricted taurine intake seems to occur through an increase in transport sites (increased Vmax) or change in flux at the transport sites, with no change in transport affinity (unaltered apparent Km).
Characteristics of NH4+ and NH3 transport across the isolated turtle urinary bladder
Authors: Schwartz J. H. , Tripolone M.
Published: December 2017

To evaluate the contribution of NH+4 movement to net ammonia flux across the turtle urinary bladder, studies were designed to determine the individual permeabilities of NH3 and NH+4. In these studies we examined the effect of varying the NH+4 concentration gradient while holding that for NH3 constant or the opposite maneuver on the unidirectional flux of ammonia. It was demonstrated that the changes in the unidirectional flux of ammonia was a linear function of the change in the concentration of the varied species. From the slope of these relationships we estimated the NH+4 permeability (4.9 X 10(-6) cm . s-1) and the NH3 permeability (2.6 X 10(-4) cm . s-1). In the absence of H+ transport the unidirectional fluxes of NH+4 were equal, and these fluxes changed in a predictable manner with the application of transepithelial electrical potentials. In the presence of H+ transport there was net NH+4 secretion due to an increase in the serosal-to-mucosal flux. Net secretion could be abolished by inhibiting H+ transport with acetazolamide. The addition of NH4Cl to the serosal solution resulted in a decrement in the rate of mucosal acidification. The subsequent addition of nonvolatile buffer to the serosal solution restored H+ transport and reduced the secretory NH+4 flux to the same extent as that produced by acetazolamide. We conclude that the turtle bladder has a significant passive permeability to NH+4. There also is apparent coupling between H+ transport and ammonia secretion. This coupling may result from titration of NH+4 in the serosal solution to NH3 by alkali generated behind the H+ pump and the diffusion of NH3 into the mucosal solution.
Effect of glucocorticoids on renal net glucose release in vivo in normal and diabetic rats
Authors: Kamiya F. , Kimura H. , Takeuchi T. , Kida K. , Nakagawa H.
Published: December 2017

The effect of glucocorticoids on renal net glucose release in vivo in normal and diabetic rats was studied by the isotope-dilution method. Administration of hydrocortisone to normal fed rats increased renal net glucose release from 0.93 +/- 0.25 to 2.27 +/- 0.21 mg . dl-1 . min-1 and increased its contribution to blood glucose from 27.0 +/- 4.5 to 46.6 +/- 4.0%. The renal net glucose release and its contribution to blood glucose in adrenalectomized rats were 0.40 +/- 0.06 mg . dl-1 . min-1 and 16.3 +/- 1.4%, respectively, significantly less than those of normal control rats, and these parameters were raised to the levels of normal control rats by the administration of hydrocortisone. In rats with streptozotocin-induced diabetes, the renal net glucose release and its contribution to blood glucose were significantly increased to 2.22 +/- 0.51 mg . dl-1 . min-1 and 46.7 +/- 4.9%, respectively, and these parameters were normalized by adrenalectomy. These data indicate that glucocorticoids play an important role in regulation of renal net glucose release and its contribution to blood glucose in both normal and diabetic rats.
Nucleotide inhibition of phosphate transport in the renal proximal tubule
Authors: Lang R. P. , Yanagawa N. , Nord E. P. , Sakhrani L. , Lee S. H. , Fine L. G.
Published: December 2017

The observation that NAD inhibits sodium-dependent phosphate (P) uptake by the luminal brush border membrane (BBM) of the proximal tubule prompted us to examine the specificity and mechanism of this process. Addition of 10(-5) M NAD to the perfusate of isolated perfused rabbit proximal straight tubules inhibited lumen-to-bath P flux by approximately 50%. ADP-ribose had an identical effect, whereas nicotinamide had no effect. ADP and 5'-AMP (10(-5) M) also inhibited P flux. Na-dependent uptake of 32P by rabbit BBM vesicles was inhibited by 0.1-0.3 mM NAD, ADP-ribose, ADP, ATP, 5'-AMP, and GDP, which were preincubated with the vesicles for 30 min. The kinetics of inhibition showed an apparent increase in the Km for P but no change in Vmax. These findings are consistent with "competitive inhibition." The nucleotides inhibited P uptake even when BBM alkaline phosphatase was inhibited by 96% with 10 mM theophylline. Evidence of nonspecific phosphatase activity was present, since incubation of BBM with 0.1 mM solution of nucleotides for 30 min resulted in an elevation of free P in the medium of approximately 0.15-0.22 mM. Correction of 32P specific activity for this change resulted in values for Km and Vmax that were not significantly different from control. The "competitive inhibition" could thus be ascribed to an isotope-dilution effect. There was no evidence to suggest that NAD caused ADP-ribosylation of the luminal membrane. These studies indicate that adenine and guanine nucleotides do not inhibit P transport by a direct action on the luminal membrane of the proximal tubule but do inhibit lumen-to-bath P flux in isolated perfused proximal tubules at concentrations of 10(-5) M. Since there is no direct inhibitory effect of these compounds at the level of the BBM, it is possible that they inhibit P transport by altering some event subsequent to the transfer of P across the luminal membrane.
Maleic acid-induced reabsorptive dysfunction in the proximal and distal nephron
Authors: Brewer E. D. , Senekjian H. O. , Ince A. , Weinman E. J.
Published: December 2017

Micropuncture and clearance studies were performed to assess reabsorptive function in the proximal and distal nephron of rats with experimental Fanconi's syndrome induced by maleic acid. Anesthetized rats were studied by free-flow micropuncture of the late proximal tubule 90-120 min after continuous intravenous administration of maleic acid, 100 mg X kg-1 X h-1. Compared with control rats, the reabsorption of sodium and phosphate was significantly reduced (P less than 0.001 and less than 0.02, respectively). Tubular fluid-to-ultrafiltrate (TF/UF) chloride concentration ratio was 1.00 +/- 0.02 compared with 1.16 +/- 0.03 (P less than 0.01) in controls, suggesting a nearly total inhibition of proximal bicarbonate reabsorption. Whole kidney fractional excretions of sodium and chloride were increased significantly (P less than 0.02) but could not be explained by enhanced delivery of these solutes out of the late proximal tubule. To assess whether distal nephron reabsorption of sodium and chloride were inhibited by maleic acid, clearance studies were performed during water diuresis in awake rats. During maleic acid administration, 200 mg X kg-1 X h-1, urine flow rate (P less than 0.02) and the fractional excretions of sodium and chloride (P less than 0.001) increased significantly, but fractional free water clearance decreased from 7.16 +/- 0.42 to 4.03 +/- 0.68% (P less than 0.001). In acetazolamide-treated control rats but not in maleic acid-treated rats with similar bicarbonaturia, the magnitude of fractional free water clearance closely approximated the simultaneously measured fractional distal delivery of chloride. These studies suggest that maleic acid inhibits reabsorption at a distal nephron site or sites as well as in the proximal tubule.
Hydrogen ion secretion by the rat distal nephron: adaptation to chronic alkali and acid ingestion
Authors: Kornandakieti C. , Grekin R. , Tannen R. L.
Published: December 2017

Isolated rat kidneys perfused at a low bicarbonate concentration were subjected to increased rates of buffer excretion, provided as creatinine, in order to examine the maximal hydrogen ion secretory capacity of the distal nephron. Preliminary experiments with kidneys from normal rats indicated that the quantity of hydrogen ion that titrated creatinine from urine pH to a pH of 6.0, designated TA-pH 6.0, provided an index of net hydrogen ion secretion by a functional segment of the distal nephron. With this technique the response of distal nephron hydrogen ion transport to ingestion of both acid and alkali loads was examined. Perfused kidneys from rats with chronic metabolic acidosis, produced by drinking 1.5% NH4Cl for 3-5 days, excreted urine with a lower pH and higher total titratable acid and TA-pH 6.0 than appropriate controls. Perfused kidneys from rats that ingested NaHCO3 for 7 days exhibited a higher urine pH and lower rates of total titratable acid and TA-pH 6.0 than controls. By contrast, kidneys from rats acutely tube-fed NaHCO3 3 h prior to study showed no change in urinary acidification parameters. Thus, chronic ingestion of an acid load stimulates, and chronic ingestion of an alkali load inhibits, the intrinsic hydrogen ion secretory capacity of the rat kidney at a distal nephron site. This intrinsic adaptation of the hydrogen ion transport mechanism is not secondary to changes in aldosterone because rats that ingested NaHCO3 chronically had higher plasma aldosterone levels than controls.
Metabolic alkalosis in models of primary and secondary hyperparathyroid states
Authors: Hulter H. N. , Toto R. D. , Ilnicki L. P. , Halloran B. , Sebastian A.
Published: December 2017

Hyperchloremic metabolic acidosis has been reported in clinical states of primary and secondary hyperparathyroidism (HPT). Acute administration of parathyroid hormone (PTH) decreases renal acidification in humans and dogs, but the renal and systemic acid-base effects of chronic HPT have not been extensively investigated. In chronically thyroparathyroidectomized (TPTX) dogs (group I), bPTH 1-5 U/kg twice daily resulted in sustained hypophosphatemia, hypercalcemia, and Cl- -resistant metabolic alkalosis that was of renal origin at least in part: delta [HCO3-]p + 4.1 +/- 0.8 meq/liter, P less than 0.01; delta [H+]p -4 +/- 1 neq/liter, P less than 0.001, days 10-12. The cumulative change (sigma delta) in net acid excretion (NAE) was +44 meq (day 9, P less than 0.05). Similarly, metabolic alkalosis of renal origin, at least in part, occurred when PTH was administered by chronic continuous intravenous infusion (group II). Since chronic administration of calcitriol in dogs results in metabolic alkalosis, plasma calcitriol concentration was measured and found not to be increased by chronic intravenous PTH administration. In intact dogs (group III), a continuous chronic intravenous infusion of the Ca2+ chelator, Na4EGTA (3.0 mmol/kg daily), substituted for an equimolar amount of prechelated EGTA (CaNa2EGTA), resulted in a model of hypocalcemic HPT and severe Cl- -resistant metabolic alkalosis: delta [HCO3-]p +9.1 +/- 1.9 meq/liter, P less than 0.05; delta [H+]p -5 +/- 1 neq/liter, P less than 0.01, days 6-8. NAE decreased significantly. Thus, whereas metabolic alkalosis induced by PTH administration could be accounted for by increased NAE (group I), EGTA-induced metabolic alkalosis was accounted for by an extrarenal mechanism of base input to extracellular fluid (group III). Neutralization of the extrarenal base input by chronic administration of HCl during the period of EGTA-induced HPT did not preclude the development of metabolic alkalosis (group V), suggesting that a renal component was present in EGTA-induced metabolic alkalosis as well as in models of primary HPT (groups I and II). During the steady state, in this group as in the groups administered PTH, the net endogenous load of acid to the systemic circulation requiring renal excretion was unchanged from control, as indicated by stable values of NAE not significantly different from control. Yet metabolic alkalosis persisted in the steady state.(ABSTRACT TRUNCATED AT 400 WORDS)
Absence of Cl- -OH- or Cl- -HCO3- exchange in the rabbit renal proximal tubule
Authors: Schwartz G. J.
Published: December 2017

Coupled entry of Na+ and Cl- into the cell may mediate salt and water absorption by the renal proximal tubule. Other leaky epithelia have been shown to have parallel luminal Na+-H+ and Cl- -OH- exchangers that can serve in concert as a major pathway for NaCl absorption. Experiments were designed to test whether Cl- -OH- or Cl- -HCO3- exchange occurs in the isolated perfused rabbit proximal convoluted tubule and thereby whether neutral transcellular NaCl absorption could be a possible mode of active transport in this segment. The studies described here make use of a lumen-to-cell gradient for Cl- to drive OH- from cell to lumen, causing an increase in the rate of H+ disappearance from the luminal fluid. Superficial proximal convoluted tubules were perfused in vitro with acidic solutions (pH 6) that were generally free of organic solutes. The bathing solution contained organics, colloid, and less than 10% of perfusate H+ concentration. H+ disappearance was calculated from the difference in pH between perfused and collected fluid, flow rate, and buffer capacity of the perfusate. The removal of Na+ from perfusate and bath reduced H+ efflux to 68% of control, a smaller effect than that noted previously in the presence of organic solutes. When Na+-containing solutions were used, bilateral replacement of Cl- by NO3-, isethionate, or SO2-(4) failed to reduce H+ efflux, but rather resulted in a 11% increase in H+ flux.(ABSTRACT TRUNCATED AT 250 WORDS)
Urea transport in isolated thick ascending limbs and collecting ducts from rats
Authors: Knepper M. A.
Published: December 2017

The use of pathogen-free rats allows the dissection and in vitro perfusion of several rat nephron segments not previously studied. In the present experiments, net urea fluxes were measured in isolated perfused cortical and medullary thick ascending limbs and cortical collecting ducts from pathogen-free Sprague-Dawley rats. No evidence for active transport of urea was found in either cortical or medullary thick ascending limbs. Permeabilities were calculated from urea fluxes measured with 5 mM urea either in the bath or perfusate and with no urea on the opposite side of the epithelium. Permeability coefficients (cm/s X 10(-5) +/- SE) in different portions of the thick ascending limb were: inner stripe, short-looped nephrons, 0.9 +/- 0.2; inner stripe, long-looped nephrons, 0.6 +/- 0.2 (not significantly different vs. short loops); outer stripe, 1.4 +/- 0.3 (P less than 0.05 vs. inner stripe); and cortical, 1.5 +/- 0.3 (P less than 0.05 vs. inner stripe). The relatively high urea permeability of thick ascending limbs in the outer stripe of the outer medulla and medullary rays is likely to permit substantial passive absorption of urea from these segments in vivo. This will contribute to dilution of the tubule fluid in thick ascending limbs and thus indirectly enhance urinary concentrating ability. In cortical collecting ducts, the urea permeability was relatively low both in the presence of 100 microU/ml arginine vasopressin in the bath (0.5 +/- 0.1 X 10(-5) cm/s) and in its absence (0.4 +/- 0.1). These permeability values are similar to values previously measured in rabbit cortical collecting ducts.
Bioenergetics of Na+ transport across frog skin: chemical and electrical measurements
Authors: Civan M. M. , Peterson-Yantorno K. , DiBona D. R. , Wilson D. F. , Erecinska M.
Published: December 2017

Enzymatically prepared split frog skins consisted purely of epithelial cells. Electrical parameters and the cell contents of ATP, ADP, phosphocreatine (PCr), creatine, inorganic phosphate, protein, and water were measured in skins maintained at room temperature. Studies were conducted under base-line conditions, 15 and 60 min after adding vasopressin, and 30 min after adding amiloride. Intracellular ionic activities and concentrations were obtained from previous results. The data demonstrated that 1) the base-line concentration ratio of PCr/ATP was 0.53 +/- 0.03; 2) the average molar free energy of hydrolysis of intracellular ATP was approximately 15.0 kcal X mol-1 under control conditions, changing by less than or equal to 3% with changes in transport; and 3) the free energy of extruding 3 mol of Na+ and accumulating 2 mol of K+ was approximately 9.8 kcal X mol-1 under base-line conditions; the difference between the molar free energies of ATP hydrolysis and of transport work remained large, despite large changes in transepithelial transport. The simplest conclusion is that the Na+ pump of frog skin operates far from equilibrium.
Effects of verapamil in models of ischemic acute renal failure in the rat
Authors: Malis C. D. , Cheung J. Y. , Leaf A. , Bonventre J. V.
Published: December 2017

This study was designed to determine whether verapamil protects renal function in experimental ischemia in the rat and, if so, whether the protection is mediated by verapamil's vasodilatory action or by an effect on renal cells independent of vascular perfusion. Inulin clearance (CIn) was examined for 3 h subsequent to 40 min of unilateral intrarenal infusion of norepinephrine (0.75 microgram X kg-1 X min-1) and 3 and 48 h subsequent to 40 min of unilateral renal pedicle clamp. In norepinephrine-induced ischemia CIn fell to 0.8 +/- 0.4% of preischemic values in saline-treated kidneys and 0.5 +/- 0.3% in verapamil post-treated kidneys. By contrast, CIn fell only to 52.3 +/- 6.5% of preischemic values in verapamil-pretreated kidneys. Verapamil pretreatment significantly counteracted the intrarenal vasoconstriction produced by norepinephrine, sustaining renal blood flow during the norepinephrine infusion. In pedicle clamp-induced ischemia verapamil pre- and posttreatment had no beneficial effect on preservation of glomerular filtration rate, whereas mannitol pretreatment was beneficial. Parallel studies in the isolated perfused rat kidney confirmed the in vivo observations. In conclusion, verapamil exerts no protective effect on renal function at 3 or 48 h when ischemia is induced by renal pedicle clamp. Likewise, verapamil administration subsequent to norepinephrine-induced ischemia is ineffective in preserving renal function. Verapamil pretreatment in norepinephrine-induced ischemia preserves renal function probably by attenuating the vasoconstrictive ischemic insult due to norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)
Response of 31P-nuclear magnetic resonance spectra of frog skin to variations in PCO2 and hypoxia
Authors: Nunnally R. L. , Stoddard J. S. , Helman S. I. , Kokko J. P.
Published: December 2017

31P-nuclear magnetic resonance (NMR) studies were conducted on split epithelial sheets of frog skins to examine the effects of hypoxia and respiratory pH variations on various phosphate-containing intracellular substrates. Frog skins were split into epithelial sheets from which the supporting tissue was removed. Epithelial sheets in either phosphate-free Cl--Ringer or phosphate-free SO2-4-Ringer were bubbled at room temperature with 100% N2, 100% O2, 2% CO2-98% O2, 5% CO2-95% O2, and 15% CO2-85% O2. The results show that the intracellular pH (pHi) with Cl- -Ringer was 7.19 and with SO2-4-Ringer was 7.42 with extracellular pH of 7.52 when bubbled with 100% O2. These pHiS indicate that H+ concentration is at least an order of magnitude less than predicted from the previously measured Nernst potential. With exposure to increasing extracellular PCO2, there is a polynomial decrease in pHi. The pHi tended to be more alkaline in SO2-4 -Ringer, suggesting the presence of a HCO-3/Cl- exchange mechanism. The ATP concentration is critically and reversibly dependent on PO2. ADP concentrations were consistently low in well-oxygenated conditions. Variable but small quantities of phosphocreatine were detected. These studies demonstrate further the potential importance in utilizing NMR spectroscopy to examine coupling of biochemical substrates to epithelial transport processes.
Efferent role of ADH in CNS-induced natriuresis
Authors: Pierce E. T. , Grekin R. J. , Mouw D. R.
Published: December 2017

Ventriculocisternal perfusion (VCP) of artificial cerebrospinal fluid (CSF) was performed in pentobarbital-anesthetized dogs. Renal function was studied in protocols consisting of a 1-h experimental period in which the animals received either CSF with an elevated sodium concentration (300 mM, high Na) via VCP or antidiuretic hormone (ADH) intravenously, bracketed by 1-h control and recovery periods. High Na VCP caused an increase in plasma ADH measured by radioimmunoassay (to 176% of control) that coincided with a natriuresis (to 180% of control). In a second set of experiments, these changes in endogenous ADH were mimicked experimentally with intravenous infusions of synthetic ADH in animals receiving continuous VCP with normal sodium artificial CSF. The dose-response relationship between log ADH and urinary sodium excretion for the intravenous ADH experiments was not different from the relationship for those experiments in which ADH was elevated as a consequence of high Na VCP. These results suggest that ADH causes part, if not all, the natriuresis induced by high Na VCP.
Glutamine transport in renal basolateral vesicles from dogs with metabolic acidosis
Authors: Windus D. W. , Cohn D. E. , Klahr S. , Hammerman M. R.
Published: December 2017

To determine whether the increased ammonia production per nephron in chronic metabolic acidosis is accompanied by augmented L-glutamine transport across the basolateral membrane of the renal cortical cell and consequent increased availability of this ammoniagenic amino acid, we measured L-[3H]glutamine transport in basolateral membrane vesicles (BLMV) isolated from kidneys of normal and acidotic dogs. Na+ -dependent electrogenic transport of L-[3H]glutamine was demonstrated in BLMV from kidneys of normal dogs that exhibited saturability over the concentration range of 25 microM to 2 mM L-glutamine. The apparent Km was 416 +/- 114 microM and Vmax was 536 +/- 129 pmol X mg protein-1 X 15 s-1. The initial rate of Na+ -dependent L-[3H]glutamine transport was increased in BLMV from kidneys of acidotic dogs, as reflected by an increased apparent Vmax. We conclude that an adaptation resulting in greater uptake of L-glutamine across the basolateral membrane of the renal cortical cell may underlie, in part, the increased rate of ammonia production per nephron seen in chronic metabolic acidosis.
Analysis of renal denervation in the hydropenic rat: interactions with angiotensin II
Authors: Pelayo J. C. , Blantz R. C.
Published: December 2017

Nephron filtration rate (SNGFR), its determinants, and proximal tubular reabsorption were measured in hydropenic Munich-Wistar rats with sham-operated (sham) or denervated (DNx) kidneys before and during the administration of [Sar1, Ala8]angiotensin II or SQ 14225. The glomerular ultrafiltration coefficient (LpA) was significantly lower in DNx than in sham rats (P less than 0.025). However, SNGFR was not altered due to an offsetting increment in transcapillary glomerular hydrostatic pressure (delta P) in DNx (P less than 0.005). The marked increment of delta P in DNx was due to an increase in the glomerular capillary hydrostatic pressure, secondary to decreased afferent arteriolar resistance. The infusion of angiotensin II inhibitors to denervated kidneys completely normalized LpA but did not alter sham values. SQ 14225 but not [Sar1, Ala8]angiotensin II infusion provided a nephron plasma flow-dependent increase in SNGFR, secondary to a striking reduction in both glomerular vascular resistances. Endogenous angiotensin II activity may be enhanced by renal denervation, and angiotensin II acts to reduce LpA in this condition and may modulate the final level of renal vascular resistances after acute renal denervation.
Vasodilation mediated by human PTH 1-34 in the spontaneously hypertensive rat
Authors: McCarron D. A. , Ellison D. H. , Anderson S.
Published: December 2017

Parathyroid hormone's cardiovascular effects were assessed in a model of experimental hypertension with known abnormalities of calcium metabolism. Mean arterial pressure (MAP) changes and serum ionized calcium responses were measured in the spontaneously hypertensive rat (SHR) and its normotensive control, the Wistar-Kyoto (WKY), following injections of synthetic human PTH 1-34. Six 22-wk-old SHR and six WKY were given intra-arterial serial injections (0.1-100 micrograms/kg) of hPTH 1-34. Both the SHR (P less than 0.001) and WKY (P less than 0.001) demonstrated log dose-dependent hypotensive responses that were maximal at 1 min, with recovery occurring between 15 and 30 min. The slopes, however, of the dose-response curves differed (P less than 0.01). The SHR experienced a greater maximal delta MAP [-93.7 +/- 2.4 (SHR) vs. -71.2 +/- 1.6 mmHg (WKY), P less than 0.01]. Furthermore, the duration of the hypotensive action of hPTH 1-34 was significantly longer (P less than 0.001) in the SHR. Even when corrected for base-line MAP the SHR demonstrated a significant (P = 0.025) enhancement of this vasodilator response at doses of 5 micrograms/kg and greater at time intervals between 3 and 9 min after injection. A transient decrease [2.25 +/- 0.10 (pre) vs. 2.17 +/- 0.11 meq/liter (1 min post), P less than 0.01] in serum ionized calcium occurred at 1 min. We conclude that hPTH 1-34 is a potent vasoactive peptide in both the normotensive WKY and the SHR. The greater maximal hypotensive response to hPTH 1-34 and the prolongation of this cardiovascular effect in the SHR may be an additional manifestation of this experimental animal's acknowledged abnormalities of cellular membrane calcium and phospholipid metabolism.
Inhibition of aldosterone-induced antinatriuresis and kaliuresis by actinomycin D
Authors: Horisberger J. D. , Diezi J.
Published: December 2017

The effects of actinomycin D on short-term response to aldosterone on sodium and potassium urinary excretion were investigated in adrenalectomized glucocorticoid-substituted anesthetized rats. Aldosterone alone (1 microgram/kg followed by sustained intravenous infusion of 1 microgram X kg-1 X h-1) entailed a simultaneous antinatriuretic and kaliuretic effect after a latent period of 30-60 min. Actinomycin D (300 micrograms/kg) administered intravenously 30 min before aldosterone inhibited both the aldosterone-induced kaliuresis and antinatriuresis and the concomitant changes in plasma potassium concentration. The administration of actinomycin D alone enhanced sodium excretion in the first hour and then induced kaliuresis. These results favor the hypothesis that mineralocorticoid effects of aldosterone on sodium and potassium excretion are closely linked and may be dependent on the same mechanisms.