bluuebunny/crossref_metadata_2025 huggingface dataset:
Superficial distal and deep nephrons in correction of metabolic alkalosis
Authors: Galla J. H. , Bonduris D. N. , Luke R. G.
Published: December 2017

Chloride is necessary and sufficient to correct alkalosis induced by dialysis vs. 0.15 M NaHCO3. To determine the contribution of the cortical (SC) distal convolution (DCT) and juxtamedullary (JM) nephrons to correction, we examined Cl and total CO2 (tCO2) transport in alkalotic Sprague-Dawley rats infused with 5% dextrose (group DM) or with 5% dextrose and 80 mM Cl (group CC); in papillary studies in alkalotic Munich-Wistar rats, 6% albumin was added to the infusate. In cortical studies, changes in plasma Cl and tCO2 were 4.9 +/- 0.7 vs. 0.7 +/- 0.9 and -6.0 +/- 0.8 vs. 0.4 +/- 0.9 meq/l and in tCO2 excretion (133 +/- 28 vs. -8 +/- 10 mueq/min) in groups CC and DM, respectively; results in papillary studies were similar. Delivery of tCO2 out of late SC DCT (CC 146 +/- 20 and DM 146 +/- 23 pmol/min) and Henle's loop (CC 145 +/- 18 and DM 202 +/- 56 pmol/min) and reabsorption within DCT (CC 15 +/- 24 and DM 45 +/- 19 pmol/min) did not differ. During correction of chloride-depletion alkalosis, the increment in bicarbonate excretion does not emanate from DCT of SC nephrons or JM nephrons but rather from the collecting duct.
Chlorothiazide effect on feedback-mediated control of glomerular filtration rate
Authors: Okusa M. D. , Persson A. E. , Wright F. S.
Published: December 2017

We examined the effect of chlorothiazide (CTZ) on the tubuloglomerular (TG) feedback system in anesthetized Sprague-Dawley rats. During infusion of CTZ (0.25 mg.kg body wt-1.min-1) we found that whole kidney glomerular filtration rate (GFR) decreased by 19% (1.0 +/- 0.1 vs. 0.8 +/- 0.1 ml/min; P less than 0.005). To asses the activity of the TG feedback system during CTZ administration we compared measurements of single-nephron (SN)GFR from tubule fluid sampled separately at proximal and distal sites. During CTZ administration, distally measured SNGFR decreased significantly by 16% (27.3 +/- 1.3 vs. 22.9 +/- 1.1 nl/min; P less than 0.025), whereas proximally measured SNGFR was unchanged. Thus the difference in SNGFR between proximal and distal determination increased during CTZ infusion (4.7 +/- 0.7 vs. 7.7 +/- 0.7 nl/min; P less than 0.025), indicating that CTZ suppresses GFR by TG feedback. Na, K, and Cl concentrations measured in the late proximal tubule fluid during control and CTZ infusions were similar. In early distal tubule fluid samples K and Cl concentrations were unaffected by CTZ infusion, whereas Na concentrations increased by 32% (47.9 +/- 2.7 vs. 63.1 +/- 2.4 mM; P less than 0.001). Proximal tubule microperfusion with 1.0 mM CTZ decreased transport rates of Na and water by approximately 40%, whereas the transport rate of Cl was not affected. In conclusion our results indicate that CTZ reduces GFR by activating TG feedback. The mechanism by which this occurs is in part due to an increase in the strength of the signal.
Induction of renal phosphoenolpyruvate carboxykinase mRNA: suppressive effect of glucose
Authors: Pollock A. S.
Published: December 2017

The mRNA for the important gluconeogenic enzyme phosphoenolpyruvate carboxykinase (GTP) (PEPCK; EC 4.1.1.32) is expressed in liver and kidney. In the kidney, acidosis is a unique and potent stimulus, whereas insulin, the major counterregulatory hormone of gluconeogenesis, has no effect. In this study, we find that oral glucose administration to rats rapidly decreases the abundance of renal PEPCK mRNA by 50–72%. This reduction takes place in normal euglycemic, in insulin-induced hypoglycemic, and in streptozotocin-induced hyperglycemic diabetic animals. The effect of glucose is not seen in the presence of metabolic acidosis, whether induced by NH4Cl or by prolonged fasting. Therefore, it appears that oral glucose loading is a physiological suppressor of renal PEPCK message abundance, although not in acidosis.
Metabolic acidosis stimulates bicarbonate reabsorption in the early proximal tubule
Authors: Santella R. N. , Gennari F. J. , Maddox D. A.
Published: December 2017

The early proximal tubule is the major site for renal bicarbonate reabsorption but little is known about the influence of acidosis on transport in this segment. This study examined early proximal bicarbonate reabsorption in rats with chronic metabolic acidosis (MA) (induced by NH4Cl administration). Rats were studied by free-flow micropuncture techniques, after varying degrees of plasma volume expansion to vary the filtered load of bicarbonate (FLHCO3). At FLHCO3 less than 700 pmol/min, both control and acidotic animals reabsorbed greater than 80% of the filtered load by 2 mm from Bowman's space. At higher FLHCO3 (700–1,100 pmol/min), reabsorption in the early proximal tubule was significantly greater in MA rats vs. control (633 +/- 26 vs. 449 +/- 24 pmol/min, between 1 and 2 mm from Bowman's space, P less than 0.001). This MA-induced stimulation of early proximal bicarbonate reabsorption was completely reversed by restoring systemic pH to normal either by acute hypocapnia or alkali infusion. Thus bicarbonate reabsorption in the early proximal tubule correlated closely with changes in systemic pH in rats with MA when bicarbonate delivery was increased by plasma expansion. The mechanism of this effect remains to be determined.
Enhanced in vivo H2O2 generation by rat kidney in glycerol-induced renal failure
Authors: Guidet B. , Shah S. V.
Published: December 2017

Aminotriazole-mediated inhibition of catalase has been used in previous studies as a measure of in vivo changes in the hydrogen peroxide generation. Using this method, we found a significantly higher inhibition of renal catalase activity at various time points (30, 60, and 90 min) in glycerol-treated rats (a well-established model for myoglobinuric acute renal failure) compared with rats treated with aminotriazole alone. The greater inhibition in the glycerol-treated group was not due to differences in aminotriazole levels. We confirmed that catalase inactivation by aminotriazole was due to formation of catalase-hydrogen peroxide intermediate (compound I) because catalase inactivation was prevented by ethanol, a competitive substrate for compound I. There were no significant differences in the aminotriazole-induced inhibition of renal cortical catalase activity in control and uranyl nitrate-treated rats, suggesting that there was no enhanced generation of hydrogen peroxide in this model of acute renal failure. Taken together, these data provide evidence for enhanced generation of hydrogen peroxide in glycerol-induced acute renal failure and suggest that the enhanced generation of hydrogen peroxide in the glycerol-induced acute renal failure is not a result of nonspecific response to tissue injury.
Evidence that intrarenal dopamine acts as a paracrine substance at the renal tubule
Authors: Siragy H. M. , Felder R. A. , Howell N. L. , Chevalier R. L. , Peach M. J. , Carey R. M.
Published: December 2017

Dopamine is synthesized within the kidney and dopamine 1 (DA1) receptors are associated with the proximal tubule. In pharmacological doses, dopamine increases renal blood flow and sodium excretion. It is possible that dopamine formed intrarenally acts locally via renal dopamine receptors to control renal function. We investigated the possible paracrine action of renal dopamine by intrarenal administration of a specific DA1 antagonist, Sch 23390, in doses confined to the kidney in conscious uninephrectomized dogs (n = 5) in metabolic balance at a sodium intake of 40 meq/day. Changes (mean +/- SE) in renal excretory and hemodynamic function in response to cumulative infusions of several doses of Sch 23390 (0.01, 0.1, 1.0, 5.0, and 10.0 pmol.kg-1.min-1) were studied. Sch 23390 at 0.01 pmol.kg-1.min-1 did not cause any changes in urinary flow rate or sodium excretion. Sch 23390 in doses from 0.1 to 10.0 mol.kg-1.min-1 caused a significant dose-dependent antidiuresis (F = 44.9, P less than 0.0001) and antinatriuresis (F = 42.1, P less than 0.0001) and a decrease in fractional sodium excretion (F = 44.2, P less than 0.0001). No changes in estimated renal plasma flow, glomerular filtration rate, plasma aldosterone concentration, plasma renin activity, or systemic arterial pressure occurred with any dose of intrarenal Sch 23390 infused into the renal artery. Rebound diuresis and natriuresis occurred after cessation of the DA1 blockade.(ABSTRACT TRUNCATED AT 250 WORDS)
Natriuretic and diuretic effects of infusion of atrial natriuretic factor in conscious dogs
Authors: Ohanian J. , Young M. A. , Shen Y. T. , Gaivin R. , Vatner S. F. , Graham R. M.
Published: December 2017

We studied the effects of 30-min infusions of the synthetic 25-amino acid atrial natriuretic factor [ANF-(102-126)] and the 28-amino acid ANF-(99-126) at 0.1 and 0.3 micrograms.kg-1.min-1 on urine flow rate, sodium excretion, and arterial pressure in conscious dogs. Each dose was administered on a separate day following a 1-h stabilization period. We also compared the effects of 60-min infusions of ANF, 0.01 micrograms.kg-1.min-1, or water infusion on separate days in conscious dogs. Arterial pressure was reduced in a dose-dependent fashion, reaching statistical significance at a dose of 0.3 micrograms.kg-1.min-1. During the 0.01-micrograms.kg-1.min-1 infusion, the plasma concentration of ANF rose approximately threefold (from 68 +/- 7 to 207 +/- 14 pg/ml), with no change in urine flow rate, sodium excretion, or arterial pressure. At a dose of 0.1 micrograms.kg-1.min-1, urine flow increased (P less than 0.05) by 0.41 +/- 0.15 ml/min, and sodium excretion rose by 72 +/- 24 mu eq/min, but not significantly, whereas plasma ANF levels rose to 1,236 +/- 229 pg/ml. At the highest dose of ANF (0.3 micrograms.kg-1.min-1) urine flow rose by 0.62 +/- 0.16 ml/min, P less than 0.05, and sodium excretion rose by 139 +/- 30 mu eq/min, P less than 0.05, whereas plasma levels of ANF rose to 2,436 +/- 320 pg/ml. In contrast, volume loading with dextran increased urine flow by 3.5 +/- 1.3 ml/min, P less than 0.05, and sodium excretion by 439 +/- 147 mu eq/min, P less than 0.05, whereas ANF rose to only 320 +/- 69 pg/ml. These results suggest that, in the conscious dog, ANF does not cause significant diuretic or natriuretic effects until plasma levels are markedly above those observed in physiological conditions. A possible explanation for the difference between this and previous studies is that the renal effects of ANF, at physiological plasma levels, are indirect and thus dependent on autonomic and hormonal (angiotensin, vasopressin, and aldosterone levels) factors governing the renal function of the animal.
Reflection coefficients and water permeability in rat proximal tubule
Authors: Green R. , Giebisch G.
Published: December 2017

Simultaneous microperfusion of proximal tubules and peritubular capillaries in kidneys of rats anesthetized with Inactin was used to measure reflection coefficients. All perfusates contained cyanide to inhibit active transport; the tubular perfusate was isotonic and the peritubular capillaries were perfused with solutions made hypertonic with NaCl, NaHCO3, L-glucose, or sodium ferrocyanide. Measurements of recollected fluid enabled a precise mean gradient and ionic fluxes to be calculated; net water flux was measured with inulin. Imposed gradients always partly dissipated. Reflection coefficients were 0.59 +/- 0.01 for NaCl, 0.87 +/- 0.04 for NaHCO3-, and 0.96 +/- 0.07 for ferrocyanide, assuming that L-glucose was 1. Water permeability of the proximal tubule was 1,030 microns/s. Ionic permeability of Cl- (21.6 +/- 1.3 X 10(-5) cm/s) was greater than that for Na+ (13.3 +/- 2.7 X 10(-5) cm/s); permeability for L-glucose was 5.4 +/- 1.3 X 10(-5), and for ferrocyanide ions 2.7 +/- 0.9 X 10(-5) cm/s. It is concluded that in rat proximal tubule both NaCl and NaHCO3 have reflection coefficients less than 1.0 and solute asymmetry across the epithelium is a significant driving force for fluid reabsorption. Furthermore the data suggest that there is a significant contribution of solvent drag to solute movement.
Acute regulation of the predominant organic solutes of the rabbit renal inner medulla
Authors: Wolff S. D. , Stanton T. S. , James S. L. , Balaban R. S.
Published: December 2017

High concentrations of organic solutes are present in the medulla of the antidiuretic kidney. However, their role in and response to acute changes in the diuretic state are unknown. In this study the organic solute content of the renal medulla was determined from extracts with the use of high-performance liquid chromatography following the acute dilution of the medullary interstitium during various forms of diuresis. After acute infusion of saline and furosemide, inner medullary urea, sodium, inositol, sorbitol, and betaine decrease significantly with no change in glycerophosphorylcholine (GPC) content. After diuresis, inner medullary urea and sodium contents eventually returned to control levels, although inositol, sorbitol, and betaine contents still remained low. Addition of antidiuretic hormone to the saline/furosemide infusion gave similar results. In contrast, induction of diuresis from mannitol infusion caused an acute decrease in all 4 organic solutes, whereas glucose infusion caused an acute decrease in all organic solutes except sorbitol. These data demonstrate that a decrease in all four organic solutes can accompany medullary dilution. However, GPC and sorbitol do not decrease when diuresis is induced by furosemide or glucose, respectively. In addition, the recovery of these compounds in a normally functioning kidney after diuresis is much slower than the regeneration of the sodium chloride and urea gradients.
Acute and chronic responses of human renal kallikrein and kinins to dietary protein
Authors: Bolin P. , Jaffa A. A. , Rust P. F. , Mayfield R. K.
Published: December 2017

Glomerular filtration rate (GFR; creatinine clearance) and renal excretion rates of active kallikrein, prokallikrein, and kinins were measured in seven normal male subjects after a week on a constant low (40 g/day)-protein diet (LP) and during a subsequent week when only protein content was increased to 140 g/day (HP). Renal kinin excretion increased from 19.7 +/- 1.2 micrograms/day on day 7 of LP to 26.0 +/- 2.5 on day 1 of HP (P less than 0.002), and this higher rate persisted during HP. Active kallikrein excretion increased from 105 +/- 16 to 171 +/- 40 micrograms/day on day 2 of HP (P less than 0.006). Prokallikrein excretion did not increase significantly until day 4 of HP, 52 +/- 16 vs. 96 +/- 38 micrograms/day (P less than 0.03). The increases in active kallikrein and kinin excretion preceded an increase in GFR, which went from 117 +/- 6.8 ml/min on LP to 130 +/- 10 ml/min on day 5 of HP (P less than 0.003). At the end of the LP diet, acute ingestion of 40 g of a casein solution produced an increase in kinin excretion after 2 h (586 +/- 64 vs. 402 +/- 33 pg/min, P less than 0.001) and further to 640 +/- 74 pg/min at 3 h (P less than 0.001). This was accompanied by an increase in GFR at 3 h (154 +/- 18 vs. 132 +/- 10 ml/min, P less than 0.05). Kinin excretion rate correlated directly with GFR during both chronic (r = 0.87) and acute (r = 0.77) studies.(ABSTRACT TRUNCATED AT 250 WORDS)
Heterogeneous response of cytoplasmic free Ca2+ in proximal convoluted and straight tubule cells in primary culture
Authors: Suzuki M. , Kawaguchi Y. , Kurihara S. , Miyahara T.
Published: December 2017

Cytoplasmic free calcium [( Ca2+]c) plays an important role in cellular signal transduction in response to hormones. The development of microfluorometric digital image analysis makes it possible to obtain an image of a calcium-indicator dye, fura-2, in a single living cell. Subconfluent primary cultured cells from isolated proximal convoluted and straight tubules were analyzed for [Ca2+]c. The basal level of [Ca2+]c was 92.0 +/- 0.82 nM in convoluted and 75.0 +/- 4.7 nM in straight tubule cells. Exposure of convoluted tubule cells to parathyroid hormone (10(-7) M) elicited a 1.4-fold transient rise in [Ca2+]c. Treatment of straight tubule cells with calcitonin (0.1 U/ml), on the other hand, evoked a 1.6-fold transient increase in [Ca2+]c. [Ca2+]c in proximal straight tubule cells did not respond to parathyroid hormone, nor did that in convoluted tubule cells to calcitonin. [Ca2+]c peaks were diminished in straight tubule cells by repeated additions of calcitonin at 5-min intervals. These hormonal responses were abolished by perfusing the cells with calcium-free solution and were not mimicked by perfusion with adenosine 3',5'-cyclic monophosphate (10(-4) M) or with forskolin (5 X 10(-5) M). The results suggest that the [Ca2+]c response to the selected peptide hormones is different in proximal convoluted and straight tubule cells in primary culture.
Calcium transport across rat inner medullary collecting duct perfused in vitro
Authors: Magaldi A. J. , van Baak A. A. , Rocha A. S.
Published: December 2017

Ca2+ transport by the inner medullary collecting duct (IMCD) of normal rats was studied using the "in vitro" microperfusion technique. Net (Jnet), lumen-to-bath (Jl----b), and bath-to-lumen (Jb----l) fluxes of Ca2+ were measured in the absence of net water absorption using 45Ca as a tracer. In the absence of an electrochemical gradient, an important net absorption of Ca2+ (11.1 +/- 1.6 pmol.cm-2.s-1), similar to the difference between the Jl----b and Jb----l, was observed by direct determination at low (5-6 nl/min) and high (12-17 nl/min) perfusion rates. The Jl----b of Ca2+ was reduced by the addition to the bath fluid of ouabain (10(-3) M) and verapamil (10(-4) M), by the presence of amiloride (10(-5) and 10(-3) M) and verapamil (10(-4) M) in the luminal fluid, or by perfusion with a Na+-free solution. Neither the presence of verapamil (10(-4) M) and ouabain (10(-3) M) in the bath nor the withdrawal of Na+ from bath and perfusion solution was able to modify the Jb----l of Ca2+. Incrementing Ca2+ bath concentration increased proportionally the Jb----l of Ca2+. Therefore Ca2+ outflux is in part dependent on Na+-K+-adenosinetriphosphatase luminal membrane Na+ transport and in part inhibited by verapamil. However, Ca2+ influx is independent of Na+ transport, is not blocked by verapamil, but is increased by Ca2+ transtubular gradient, indicating the presence of a passive diffusion mechanism.
Effect of acute renal decapsulation on pressure natriuresis in SHR and WKY rats
Authors: Khraibi A. A. , Knox F. G.
Published: December 2017

The objective of these experiments was to study pressure natriuresis in the Wistar-Kyoto (WKY) and the spontaneously hypertensive rat (SHR) during acute bilateral renal decapsulation, a maneuver that partially blocks the increase in renal interstitial hydrostatic pressure (RIHP). In control WKY rats (n = 7), at renal perfusion pressure (RPP) of 105 +/- 0.7 and 125 +/- 1.1 mmHg, RIHP increased from 4.4 +/- 0.4 to 7.2 +/- 0.7 mmHg (P less than 0.05) and fractional excretion of sodium (FENa) increased from 0.23 +/- 0.05 to 1.32 +/- 0.14% (P less than 0.05). Acute bilateral renal decapsulation (n = 6) blunted the increase in RIHP observed when RPP was increased in control WKY rats and abolished the pressure natriuretic and diuretic response. When RPP was allowed to increase from 106 +/- 0.8 to 130 +/- 2.2 mmHg in the WKY rats with decapsulated kidneys, RIHP increased from 3.8 +/- 0.5 to 4.3 +/- 0.4 mmHg but FENa did not significantly change (0.31 +/- 0.12 to 0.43 +/- 0.13%). In control SHRs (n = 7), at RPPs of 135 +/- 0.8 and 163 +/- 3.0 mmHg, RIHP was 4.4 +/- 0.4 and 5.0 +/- 0.6 mmHg (NS) and FENa was 0.41 +/- 0.10 and 0.82 +/- 0.17% (P less than 0.05). Renal decapsulation in the SHR did not affect the blunted relationships between RPP, RIHP, and FENa; at RPPs of 135 +/- 0.3 and 162 +/- 2.9 mmHg (n = 7), RIHP was 4.4 +/- 0.6 and 4.7 +/- 0.5 mmHg (NS) and FENa was 0.43 +/- 0.10 and 0.95 +/- 0.22% (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Increased oxidative metabolism in renal tubules from spontaneously hypertensive rats
Authors: Brazy P. C. , Klotman P. E.
Published: December 2017

Genetic hypertension in the rat is associated with abnormal renal function. This may be due to systemic hypertension or to intrinsic alterations in the kidney. Therefore, we examined intrinsic rates of oxidative metabolism in renal cortical tubules isolated from spontaneously hypertensive rats (SHR) and age-matched normotensive controls (WKY) before, during, and after the development of hypertension. We examined tubule function in SHR and WKY treated with antihypertensive agents to block the development of hypertension. During the early phase of hypertension (ages 7-8 wk), SHR tubules have intrinsic rates of oxygen consumption that are 15-25% greater than that of WKY. Ouabain-sensitive rates of oxygen consumption, an index of sodium entry, and Na+-K+-ATPase activity were not increased by 17%. Reduction of blood pressure with drugs did not abolish these differences in oxidative metabolism. Addition of exogenous arachidonic acid (1 microM) did reduce the metabolic differences between 8-wk-old SHR and WKY tubules. Norepinephrine (1 microM) had a greater stimulatory effect on oxygen consumption rates in tubules from hypertensive SHR. The relationship of these metabolic differences to the development of hypertension remains unclear.
Cyclosporine augments renal mitochondrial function in vivo and reduces renal blood flow
Authors: Lemmi C. A. , Pelikan P. C. , Sikka S. C. , Hirschberg R. , Geesaman B. , Miller R. L. , Park K. S. , Liu S. C. , Koyle M. , Rajfer J.
Published: December 2017

The in vivo action of cyclosporine A (CS) on rat renal cortical mitochondria was investigated. CS (30 mg.kg-1.day-1) given orally to rats for 30 days caused an augmentation of renal mitochondrial oxidative phosphorylation. The ADP-stimulated respiratory rate was increased by 37.0% with glutamate plus malate as respiratory substrates (P less than 0.025) but not with succinate-supported respiration, indicating enhancement of mitochondrial complex I activity. This reaction may be a response to the 32.5% reduction of renal blood (P less than 0.005) in the CS-treated group, possibly serving to maximize ATP synthesis during ischemia. Ligation-induced decreases in renal blood flow also resulted in enhancement of mitochondrial complex I activity.
Relationship between intracellular pH and ammonia metabolism in LLC-PK1 cells
Authors: Sahai A. , Laughrey E. , Tannen R. L.
Published: December 2017

Previous studies from our laboratory have confirmed that cultures of LLC-PK1 cells exhibit pH-responsive alterations in ammonia metabolism produced by changes in media bicarbonate concentration. To further elucidate the mechanism of ammonia regulation, studies were carried out using parallel cultures of still and rocked LLC-PK1 cells subjected to acute alterations in media pH by either metabolic or respiratory acid-base manipulations. When media pH was altered by modifying PCO2 levels, the response of ammonia and alanine production by rocked culture was identical to the changes observed with metabolic acid-base maneuvers. Furthermore, both metabolic and respiratory acute acidosis resulted in a fall of intracellular alpha-ketoglutarate concentrations in these cells. In contrast, standard still cultures subjected to acute acidosis/alkalosis by metabolic and respiratory manipulations did not exert any significant change in ammonia and alanine production or in intracellular alpha-ketoglutarate concentration. Measurements of intracellular pH (pHi) by the 5,5-[2-14C]dimethyloxazolidine-2,4-dione method in rocked cells demonstrated changes in pHi parallel to media pH changes induced by both metabolic and respiratory acid-base maneuvers. Despite the absence of pH-responsive ammonia-genesis in still cultured cells the pHi values were altered in a fashion similar to their rocked counterparts, indicating the lack of an effect of the pHi signal on ammonia metabolism.
Native tubular fluid attenuates ANF-induced inhibition of tubuloglomerular feedback
Authors: Pollock D. M. , Arendshorst W. J.
Published: December 2017

The effect of atrial natriuretic factor [ANF-(1–28); 0.25 microgram.kg-1.min-1] on tubuloglomerular feedback (TGF) and the efficiency of renal blood flow (RBF) autoregulation was determined in anesthetized euvolemic rats. In microperfusion studies, ANF dramatically inhibited (greater than 80%) feedback-mediated decreases in single-nephron glomerular filtration rate (SNGFR) and stop-flow pressure (Psf) when Henle's loop was perfused at 0–48 nl/min with artificial fluid. The sigmoidal relationship between Psf and loop perfusion during control was shifted to a linear relation during ANF; reactivity was almost nonexistent and no inflection point could be discerned. ANF almost completely blocked maximum Psf and SNGFR responses to loop perfusion at rates greater than 24 nl/min. In contrast 30 nl/min loop perfusion with native proximal tubular fluid obtained during ANF infusion restored maximum TGF activity to 70% of control levels. During ANF administration, the paired Psf responses to native and artificial perfusate were significantly different (-5.3 vs. -0.8 mmHg, P less than 0.001), compared with similar responses during control conditions (-7.6 vs. -8.3 mmHg, P greater than 0.1). In free-flow studies, ANF increased proximally and distally measured SNGFR equally. The constancy of the proximal-distal SNGFR difference (10.3 vs. 9.3 nl/min) in the presence of increased distal fluid delivery suggests partial inhibition of TGF during ANF administration. ANF elevated Psf but did not affect basal RBF or the RBF autoregulatory index over an arterial pressure range of 130–70 mmHg. These results indicate that 1) RBF autoregulation is efficiently maintained during ANF infusion when preglomerular vessels are vasodilated and TGF is inhibited by approximately 30%; 2) an endogenous factor(s) in native proximal tubular fluid may attenuate ANF-induced inhibition of TGF; and 3) microperfusion studies using artificial fluid significantly overestimate the net in vivo effect of ANF on TGF.
Cyclosporine augments renal but not systemic vascular reactivity
Authors: Garr M. D. , Paller M. S.
Published: December 2017

Renal vasoconstriction and hypertension are major side effects of cyclosporine. We tested the acute effects of cyclosporine on renal and systemic vascular reactivity to norepinephrine, angiotensin II, and arginine vasopressin. Renal vascular reactivity was tested in anesthetized Sprague-Dawley rats with denervated kidneys. Renal blood flow was measured with an electromagnetic flow probe in response to graded intra-arterial infusions of vasoconstrictors before and after intravenous administration of cyclosporine. Cyclosporine augmented the decrease in renal blood flow and the increase in renal vascular resistance produced by intrarenal norepinephrine, angiotensin II, and arginine vasopressin. In these studies, systemic blood pressure did not change and cyclosporine caused no direct change in basal renal blood flow. In contrast, in conscious animals, cyclosporine did not increase the pressor response to intravenous norepinephrine or to angiotensin II. Rather, cyclosporine caused enhanced baroreflex slowing of heart rate and a decrease in the pressor response to both norepinephrine and angiotensin II. Even when the baroreceptor reflex was blocked by pentolinium, the pressor response to norepinephrine in cyclosporine-treated animals was diminished compared with vehicle-treated animals. Therefore, although cyclosporine augmented renal vasoconstriction in response to norepinephrine, angiotensin II, and arginine vasopressin, it did not acutely increase the systemic vascular response to these agents. Enhanced renal vascular responsiveness is an additional mechanism for cyclosporine-mediated renal vasoconstriction. Lack of enhanced peripheral vascular responsiveness suggests that hypertension is not likely to be due to direct effects on the systemic vasculature and is more likely to be a consequence of renal functional impairment.
Fluorescein transport in isolated proximal tubules in vitro: epifluorometric analysis
Authors: Sullivan L. P. , Grantham J. A. , Rome L. , Wallace D. , Grantham J. J.
Published: December 2017

An epifluorometric method was used to quantify the bidirectional fluxes of fluorescein across the basolateral surfaces of nonperfused rabbit tubule segments in vitro. Proximal S2 segments, but not cortical collecting tubules or cortical thick ascending limbs, accumulated fluorescein to levels in cytoplasm over 100-fold greater than in the external medium. The rate of intracellular fluorescein accumulation was dependent on the concentration of the ligand in the external bath. The apparent Km was 10 microM and the Vmax was 623 x 10(-6) mol.min-1.l-1. Probenecid and ouabain inhibited fluorescein accumulation. We conclude that fluorescein is transported into the cytoplasm of proximal tubules by basolateral mechanisms that share features in common with the classical organic anion system. This fluorescent compound offers some unique advantages for the study of the organic anion transport system in intact cells.
Arterial pressure effects on preglomerular microvasculature of juxtamedullary nephrons
Authors: Carmines P. K. , Inscho E. W. , Gensure R. C.
Published: December 2017

Videomicroscopic and micropuncture techniques were utilized to determine segmental microvascular responses of in vitro blood-perfused juxtamedullary nephrons to step changes in renal arterial perfusion pressure (PP). At a PP of 104 +/- 2 mmHg, inside diameters of arcuate arteries (ARC), interlobular arteries (ILA), and afferent arterioles (AFF) averaged 68.6 +/- 6.4, 35.7 +/- 1.5, and 20.4 +/- 2.3 microns, respectively. Variations in PP within the range of 70-180 mmHg elicited alterations in microvessel diameters with the following slopes: ARC, -0.15 micron/mmHg; ILA, -0.13 micron/mmHg; and AFF, -0.14 micron/mmHg. In other experiments, intravascular pressures were measured during changes in PP. Glomerular capillary pressure was well regulated (slope = 0.19 +/- 0.03 mmHg/mmHg), and mid-AFF pressure was partially regulated (slope = 0.60 +/- 0.17 mmHg/mmHg); however, pressure measured at the ILA-AFF branch point responded passively to changes in PP (slope = 0.95 +/- 0.06 mmHg/mmHg). These observations reveal that, although the entire preglomerular vasculature of juxtamedullary nephrons is capable of actively responding to changes in PP, afferent arterioles are responsible for the predominant resistance adjustment throughout the normal autoregulatory range.
PTH receptor coupling to phospholipase C is an alternate pathway of signal transduction in bone and kidney
Authors: Dunlay R. , Hruska K.
Published: December 2017

The parathyroid hormone (PTH) receptor is coupled via a guanine nucleotide-binding regulatory protein (G protein) to phospholipase C (PLC). Binding of PTH to its receptor leads to activation of PLC with the subsequent hydrolysis of phosphatidylinositol 4,5-bisphosphate to inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 generation leads to the release of intracellular calcium stores, which produces an increase in the intracellular calcium concentration. DAG activates protein kinase C (PKC). Both IP3 metabolites and PKC may play a role in returning the intracellular calcium concentration back to base line, by stimulating the movement of calcium from the intracellular to the extracellular compartment, as well as by sequestering calcium within intracellular organelles. PKC appears to be important in the development of desensitization and downregulation of the PTH receptor to PTH. Activation of PLC may be important in modulating the well-known effects of PTH on bone and kidney and also may be relevant to recently described actions, such as the possible role of PTH as a growth factor in skeletal tissue. Important issues that need to be addressed in this field include 1) characterization of the PTH receptor, 2) the possible role of low-molecular-weight G proteins in PTH signal transduction, and 3) further description of the role of alternate pathway signal transduction in producing the effects of PTH.
Quantitation of total carbon dioxide in nanoliter samples by flow-through fluorometry
Authors: Star R. A.
Published: December 2017

A new ultramicrofluorometric assay for the measurement of picomole amounts of total CO2 is described. The assay is based on a sequence of two linked enzymatic reactions: HCO3 reacts with phosphoenolpyruvate forming oxaloacetate, and oxaloacetate is then converted to malate with associated oxidation of NADH to NAD+. The fluorescence of NADH is measured in a modified ultramicrofluorometer. The HCO3 content of the sample is proportional to the decrease in NADH fluorescence. The method can resolve differences as small as 5.5 pmol total CO2 in 3-nl samples containing 0-160 pmol. The assay is 5- to 10-fold more sensitive than the widely used microcalorimetric assay. The assay can also measure total CO2 in biological samples. The assay will be useful in measuring transepithelial total CO2 transport in short distal nephron segments with low rates of total CO2 transport without resorting to extremely long collection times.
A theoretical approach to analyze pressure equilibria in the interstitium
Authors: Gilanyi M. , Kovach A. G.
Published: December 2017

Inherent problems concerning the interstitial fluid pressure (IFP) are reinvestigated on theoretical grounds. Analyzing the thermodynamic and mechanical equilibria in the interstitium, it is concluded that IFP includes a pressure term originating from the elastic forces and an osmotic pressure term. A quantitative relationship is established between the IFP and all of the parameters responsible for the changes in the recorded pressure. The theoretical results suggest that, under control conditions, 1) there are no permanently existing free fluid spaces, 2) the gel pressure is atmospheric, and 3) the fluid equilibration techniques measure an osmotic pressure difference between the gel phase and the fluid phase created artificially by any of the pressure measuring devices. The pressure response during acute volume changes is attributed to the changes in the osmotic pressure term, gel volume, and elasticity. Volume and elasticity changes are reflected in the recorded IFP as promptly developing and permanent effects; on the other hand, osmotic processes result in slowly developing and transient effects. The volume-pressure relationship is also analyzed.
Dietary bicarbonate reduces rat distal nephron acidification evaluated in situ
Authors: Wesson D. E.
Published: December 2017

Whether altered reabsorption of bicarbonate by the superficial distal nephron contributes to the renal response to a chronic dietary bicarbonate challenge is not known. These micropuncture studies were done in control, NaHCO3-loaded, and NaCl-loaded Munich-Wistar rats to determine whether this dietary maneuver altered acidification in this nephron segment as evaluated in situ. Urinary bicarbonate excretion of NaHCO3-loaded animals was higher than control for each day of a 7-day study period, but bicarbonate excretion for animals identically loaded with NaCl was not sustained above control. Bicarbonate transport by the superficial distal nephron was assessed using paired collections from this segment. Net bicarbonate reabsorption was observed in all three groups. Reabsorption was lower in NaHCO3-loaded vs. control (11 vs. 25 pmol/min, P less than 0.01) but that for NaCl-loaded animals was not. The data indicate that reduced reabsorption of bicarbonate by the superficial distal nephron of rats contributes to the renal response to a chronic dietary bicarbonate challenge as evaluated in situ.
Role of protein kinase C in proximal bicarbonate absorption and angiotensin signaling
Authors: Liu F. Y. , Cogan M. G.
Published: December 2017

Using in vivo microperfusion in the proximal convoluted tubule (PCT) of the Munich-Wistar rat, we investigated the impact of varying protein kinase C (PKC) activity on the rate of bicarbonate reabsorption and on its regulation by angiotensin II. Activation of PKC with luminal perfusion of phorbol 12-myristate 13-acetate (PMA, 5 x 10(-7) M) caused bicarbonate absorption in the S1 PCT to increase by 25%, from 346 +/- 7 to 432 +/- 4 peq.mm-1.min-1 (P less than 0.001), without affecting intracellular cAMP level. Another PKC stimulator, dioctanoylglycerol, had the same effect. Inhibition of PKC activity with luminal perfusion of 5 x 10(-6) M sphingosine had the opposite effect, decreasing bicarbonate absorption by 45% to 190 +/- 2 peq.mm-1.min-1 (P less than 0.001). Pretreatment with PMA or with sphingosine each attenuated by approximately one-third the bicarbonate absorptive response usually observed following angiotensin II administration. Similar results for the action of PKC, but of smaller magnitude, were found in the S2 PCT. In conclusion, activation of PKC increases bicarbonate and water absorption in the S1 and S2 PCT in vivo, and PKC may participate in as much as one-third of the transport stimulation induced by angiotensin II.
Effects of chronic volume expansion and enalapril on chronic cyclosporine nephropathy
Authors: Gillum D. M. , Truong L.
Published: December 2017

Prolonged treatment with cyclosporine (CS) results in an irreversible renal lesion consisting of interstitial fibrosis and tubular atrophy, as well as prominent hyperplasia of the juxtaglomerular apparatus (JGA). Ischemia to the tubulointerstitial compartment caused by intense CS-mediated renal vasoconstriction may contribute significantly to the development of this lesion. To explore the potential role of volume contraction and activation of the renin-angiotensin system (RAS) in the genesis of this lesion, we have employed a recently described rodent model of chronic cyclosporine nephropathy (CCN). Over 28 days of CS therapy, animals received plain drinking water, 1% saline, or enalapril (ENAL), 50 mg/l in drinking water. At the end of 28 days, Na+ balance in saline-treated animals was markedly positive, and plasma volume was increased; however, glomerular filtration rate (GFR) did not change, and the tubulointerstitial lesion and JGA hyperplasia as evaluated by morphometric techniques were unaffected. Enalapril-treated animals were relatively hypotensive with lower GFR than CS controls. Enalapril conferred no protection against the development of tubulointerstitial disease and exacerbated the development of JGA hyperplasia and hyperkalemia. We conclude that volume contraction is not an important contributor to the reduced GFR, tubulointerstitial lesion, or JGA hyperplasia associated with long-term CS treatment. Blockade of the RAS also conferred no protection against the development of tubulointerstitial disease but resulted in worsening of JGA hyperplasia and hyperkalemia.
Na+(Li+)-H+ exchange in rat renal cortical vesicles with endosomal characteristics
Authors: Sabolic I. , Brown D.
Published: December 2017

Preparations of rat renal cortical endocytic vesicles, loaded with fluorescein isothiocyanate-labeled dextran (FITC-dextran) in vivo had an ATP-dependent N-ethylmaleimide (NEM)-sensitive H+ pump and, in addition, showed a limited activity of an electroneutral Na(+)-H+ and Li(+)-H+ exchanger. However, the majority of FITC-dextran-containing vesicles possessed only the H+ pump. The H+ pump and the electroneutral Na+(Li+)-H+ antiporter colocalized in only a small proportion of FITC-dextran-containing vesicles. These vesicles also exhibited marked electrically coupled Na+, Li+, and H+ movement due to conductances in the vesicle membrane for these cations. As measured by the acridine orange fluorescence quench method, the electroneutral Na(+)-H+ exchange in endosomal preparations obeyed hyperbolic kinetics with an apparent Michaelis constant (Km) for Na+ of 5.9 mM and resembled that of brush-border membrane vesicles (BBMV) isolated from the same tissue (Km for Na+, 3.7 mM). The endosomal Na+(Li+)-H+ exchange was not affected by the presence or absence of ATP or NEM. However, Li+, added before or simultaneously with Na+, inhibited the endosomal Na(+)-H+ antiporter. The Na+(Li+)-H+ antiporter was insensitive to extravesicular amiloride but was partially inhibited by intravesicular amiloride. Acidic buffers stimulated the activity of the electroneutral exchanger. We found that vesicles with similar characteristics contaminate preparations of right-side-out BBMV. We conclude that the vesicles with endosomal characteristics, which contain both a vacuolar-type H+ pump and the Na+(Li+)-H+ antiporter, are either a special pool of endocytic vesicles responsible for the trafficking of the exchanger between intracellular and luminal membranes or are inside-out BBMV that form during the homogenization of the tissue.
1/f fluctuations in arterial pressure and regulation of renal blood flow in dogs
Authors: Marsh D. J. , Osborn J. L. , Cowley A. W.
Published: December 2017

To determine whether renal blood flow is regulated against spontaneous fluctuations in arterial pressure and to estimate the frequency band of the regulation, we measured arterial pressure and renal blood flow continuously over several days in conscious dogs. Mean arterial blood pressure showed broad band fluctuations and behaved as a 1/f process, indicating that the blood pressure record is a fractal curve and therefore scale invariant. The fluctuations in arterial pressure caused attenuated fluctuations in renal blood flow; the gain was about -6.5 +/- 0.5 dB through all sampled frequencies greater than or equal to 4 cycle/day. The kidney did not attenuate the blood pressure signal at the lowest frequencies. The results show that renal blood flow is better regulated against fluctuations in pressure at frequencies greater than or equal to 4 cycle/day than it is at lower frequencies. Although there are no direct tests of the underlying regulatory mechanisms, we argue that the responses are generated locally and can be identified with renal autoregulation.
Measurement of renin secretion in single perfused rabbit glomeruli
Authors: Bock H. A. , Hermle M. , Fiallo A. , Osgood R. W. , Fried T. A.
Published: December 2017

A new technique is presented that allows the measurement of the renin secretion rate of single rabbit glomeruli during in vitro perfusion at controlled afferent arteriolar perfusion pressure. Rabbit glomeruli with intact afferent arteriole and Bowman's capsule are obtained by microdissection and cannulated with a pipette system that allows continuous afferent arteriolar pressure measurement. The renin secretion rate of 10 glomeruli, perfused at 40 mmHg, was measured in 15-min intervals with an antibody-trapping microassay. Renin secretion rate was low relative to total renin content (1.2-2.0% of content/perfusion h) and increased three- to fivefold in response to isoproterenol (10(-5) M). The afferent arteriole contracted to norepinephrine (10(-5) M) in each instance. This novel, although difficult, technique allows the study of renin release in vitro at controlled perfusion pressure, without the interfering effects of the macula densa, arterial angiotensin II, and the adrenergic nervous system. It should allow a new perspective on issues such as the pressure-flow dependence of renin release and the interaction of the afferent arteriolar endothelium with the renin-secreting juxtaglomerular cells.
Acetazolamide and insulin alter choroid plexus epithelial cell [Na+], pH, and volume
Authors: Johanson C. E. , Murphy V. A.
Published: December 2017

Agents that inhibit or stimulate Na+ transport were tested for their effects on the ionic composition and volume of the in vivo choroid plexus (CP) epithelium. Ketamine-anesthetized adult Sprague-Dawley rats treated 1 h with acetazolamide or insulin were analyzed for choroid cell [Na+]i, [HCO3-]i, and pHi (dimethadione method); for transmembrane Na+ and H+ gradients; and for the kinetics of penetration of 22Na from plasma to plexus epithelium to CSF. Acetazolamide (25 mg/kg) reduced [Na+]i by 5-10 mmol/l and substantially elevated [HCO3-]i and pHi; the concurrent 22Na uptake by the in vivo choroid plexus and CSF, as quantified by the transfer coefficient, Kin (ml.g-1.h-1), was curtailed by 55-60%. Such effects on Na+ transport and distribution are likely secondary to the alkalinization of pHi induced by carbonic anhydrase inhibition. Conversely, insulin (3 U/kg ip) stimulated Na+ transport, i.e., manifested as enhanced uptake of 22Na from plasma to choroid cell and increased [Na+]i. For various treatments altering the basolateral membrane H+ gradient, the regression analysis of the 22Na Kin vs. log [H+]i/[H+]ISF (where ISF is interstitial fluid) was significant at P less than 0.01. This is consistent with effects mediated by Na(+)-H+ exchange. K+ and Cl- redistribution phenomena were coincident with altered Na+ transport, as choroidal cells retained K+, Cl-, and H2O after acetazolamide but lost K+, Cl-, and H2O with insulin treatment. A model is presented relating alterations in CP Na+ transport, KCl content, and cell volume. Overall, the findings encourage the postulate for effects of these drugs on Na+ transport basolaterally, either indirectly by attenuating [H+]i/[H+]ISF (acetazolamide) or directly by accelerating Na+ transport (insulin).
The role of adenosine in HgCl2-induced acute renal failure in rats
Authors: Rossi N. , Ellis V. , Kontry T. , Gunther S. , Churchill P. , Bidani A.
Published: December 2017

It has been proposed that adenosine mediates the renal hemodynamic changes in acute renal failure (ARF) and that these changes are pathogenic in reducing glomerular filtration rate. Consistently, adenosine-receptor antagonists such as theophylline have been shown to have protective effects in several experimental models of ARF. The present experiments were designed to explore the potential role of adenosine in HgCl2-induced ARF in rats. In isolated perfused rat kidneys, HgCl2 increased adenosine production and induced a concentration-dependent vasoconstriction. However, the vasoconstriction was unrelated to adenosine production and was not antagonized by theophylline. During the initiation phase of HgCl2-induced ARF in intact rats (first 4 h after injection), theophylline failed to reverse the reduction in inulin clearance, and this failure could not be attributed to a loss of vascular responsiveness to adenosine, since N6-cyclohexyladenosine, a receptor agonist, produced a further reduction in inulin clearance. Furthermore, theophylline actually had deleterious effects during the maintenance phase of HgCl2-induced ARF in intact unanesthetized rats, as evidenced by higher mean serum creatinine values in theophylline-injected rather than in saline-injected rats, on both the second and third days after HgCl2 injection. Therefore HgCl2 acutely increases renal adenosine production, but increased adenosine does not mediate acute HgCl2-induced renal vasoconstriction, and adenosine-receptor antagonism does not have protective effects during the initiation or the maintenance phases of HgCl2-induced ARF in rats. These results provide no support for the hypothesis that increased adenosine mediates the hemodynamic changes in HgCl2-induced ARF.