bluuebunny/crossref_metadata_2025 huggingface dataset:
Absence of Cl-OH exchange and NaCl cotransport in rabbit renal microvillus membrane vesicles
Authors: Seifter J. L. , Knickelbein R. , Aronson P. S.
Published: December 2017

Cl-transport was studied in microvillus membrane vesicles isolated from the rabbit renal cortex. Inwardly directed K+ gradients in the presence of the K+ ionophore valinomycin (Val) enhanced 10 mM 36Cl uptake 2.5-fold, confirming a Cl- conductive pathway. An inwardly directed H+ gradient (pHin 7.5, pHout 6.0) stimulated 10 mM Cl- uptake 1.5-fold compared with pHin = pHout = 6.0. However, this H+ gradient stimulation of Cl- uptake appeared secondary to the H+ diffusion potential rather than to Cl-OH exchange, as it was abolished by Val and K+in = K+out. Additional evidence against Cl- transport via anion exchange was the failure of an inwardly directed Cl- gradient to generate an inside-acid pH gradient as monitored by quenching of acridine orange fluorescence. Cl- influx was the same in the presence of inwardly directed gradients of Na+, K+, Cs+, Li+, and Rb+, arguing against NaCl cotransport. Finally, conductive Cl- transport was reduced by the inhibitors furosemide, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid. These data indicate the presence of an inhibitor-sensitive, conductive mode of Cl- transport but fail to demonstrate significant pathways for Cl- OH exchange or NaCl cotransport in rabbit renal microvillus membrane vesicles.
Lead flux through the kidney and salivary glands of rats
Authors: Craan A. G. , Nadon G. , P'an A. Y.
Published: December 2017

The blood disappearance curve of lead injected intravenously into rats and its appearance curve in the saliva reflect a three-compartment open model. Urinary elimination rate showed many fluctuations in the first 10 days but decreased progressively afterward. In clearance experiments, with low lead infusion (4 micrograms/min), renal reabsorption accounted for nearly all the filtered lead load, and salivary secretion was on the order of 1 ng/min. Experiments with renal and salivary tissue fragments indicated maximal accumulation in both tissues. Contrary to salivary tissue uptake, renal accumulation of lead decreased in the presence of KCN and 2,4-dinitrophenol, and in Na+-deficient media. Renal lead uptake contains, therefore, an important energy-dependent component. In vitro evidence that the lead transport mechanisms of the kidney and salivary glands are fundamentally different is consistent with the results of the pharmacokinetic study. The resemblance between the early profile of salivary lead secretion and its disappearance from the blood indicates that salivary glands represent diffusion barriers for the metal, in contrast to the kidney where lead uptake may be influenced by energy- and metabolism-dependent mechanisms.
Hypothalamic sodium-transport inhibitor is a high-affinity reversible inhibitor of Na+-K+-ATPase
Authors: Haupert G. T. , Carilli C. T. , Cantley L. C.
Published: December 2017

Bovine hypothalamus contains a stable, low molecular weight substance with ouabain-like properties. To further study its mechanism of action and potential physiological importance we examined its effects on purified Na+-K+-ATPase in a kinetic coupled-enzyme assay. Under optimal conditions up to 95% of Na+-K+-ATPase activity could be inhibited by the factor. Mg2+ is required for maximal inhibitory activity, but ligand requirements for optimal activity are otherwise distinct from those of both ouabain and vanadate. Inhibition is reversed by high concentrations of sodium chloride plus EDTA. Kinetic analysis yielded a Ki = 1.4 nM. The hypothalamic factor is a high-affinity reversible inhibitor of Na+-K+-ATPase, being at least as potent as the cardiac glycoside ouabain and may be a circulating inhibitor of sodium transport, which appears to be associated with experimental volume-expanded hypertension and human essential hypertension.
Glomerular prostaglandin formation in two-kidney, one-clip hypertensive rats
Authors: Stahl R. A. , Helmchen U. , Paravicini M. , Ritter L. J. , Schollmeyer P.
Published: December 2017

In vitro prostaglandin (PG) and thromboxane B2 (TXB2) formation by isolated glomeruli from normotensive (N) and two-kidney, one-clip hypertensive (2K,1C) rats was determined. When calculated on the basis of glomerular protein content, PGE2, 6-keto-PGF1 alpha and TXB2 production of glomeruli from clipped kidneys was significantly greater than PG and TXB2 formation of glomeruli from the untouched kidneys. When PG and TXB2 formation was calculated per amount of glomeruli, only PGE2 formation was found to be significantly greater in clipped kidneys. No severe damage of glomerular structure was found in the kidneys when studied by light microscopy. In additional in vivo studies, the effect of the cyclooxygenase inhibitor indomethacin on blood pressure and glomerular filtration rate (GFR) was evaluated. Following indomethacin GFR in 7 of 13 clipped kidneys of 2K,1C rats decreased from 363 +/- 77 to 188 +/- 51 microliter/100 g body wt, whereas six kidneys developed anuria. No effect of cyclooxygenase inhibition on GFR was found in N rats and in untouched kidneys of 2K,1C rats. Mean arterial blood pressure in 2K,1C hypertension fell significantly, from 158 +/- 10 to 135 +/- 7 mmHg, after cyclooxygenase inhibition. No effect was seen in N rats. The data suggest that increased glomerular PG formation in the clipped kidneys of 2K,1C rats is involved in the pathogenesis of hypertension in this animal model.
Atrial extracts increase glomerular filtration rate in vivo
Authors: Beasley D. , Malvin R. L.
Published: December 2017

We measured the effect of a constant infusion of rat atrial extract on the glomerular filtration rate (GFR), renal plasma flow (RPF), and plasma renin concentration (PRC) of bioassay rats. The infusion rate of the atrial extract was 0.038 ml/min, which represented 1.25 mg of homogenized atrial tissue/min. To ensure that dead space was cleared, clearance measurements during the atrial extract infusion were not begun until urine flow had increased and 300 microliter of urine had been excreted. In the first series of rats, control GFR was 0.69 +/- 0.05, increased to 1.04 +/- 0.06 during infusion of atrial extract, and then decreased to 0.72 +/- 0.08 ml X min-1 X 100 g-1 during the recovery period. In a second series, RPF was also measured. GFR increased from 0.92 +/- 0.02 to 1.15 +/- 0.05 ml X min-1 X 100 g-1, while RPF was unchanged. In both series, the increase in GFR was statistically significant. Constant infusion of atrial extracts had no significant effect on PRC. These studies provide evidence that an atrial factor can cause a large increase in GFR, which may contribute to the natriuretic effect of atrial extracts.
Response of isolated renal arterioles to acetylcholine, dopamine, and bradykinin
Authors: Edwards R. M.
Published: December 2017

The effect of acetylcholine (ACh), dopamine (DA), and bradykinin (BK) on vascular tone was examined in interlobular arteries and superficial afferent and efferent arterioles isolated from rabbit kidney. A single microvessel was dissected and cannulated, and lumen diameter was measured at a fixed intraluminal pressure. ACh caused a dose-dependent relaxation of norepinephrine-induced tone in all three vessel types. Significant relaxation (10-20%) was observed with 10(-8) M ACh and higher concentrations caused complete relaxation. In afferent and efferent arterioles DA caused a dose-dependent relaxation that was indistinguishable from the one caused by ACh. However, DA was much less effective on interlobular arteries. Significant relaxation was not observed until 10(-5) M DA, and 10(-4) M caused only a 30-40% relaxation. In afferent arterioles atropine blocked the effect of ACh, and metoclopramide selectively inhibited DA-induced relaxation. BK (10(-9) to 10(-5) M) caused a dose-dependent relaxation of norepinephrine-induced tone only in efferent arterioles. BK, either in the bath or lumen, had no effect on the preglomerular microvessels. ACh and DA also caused relaxation of afferent arterioles with spontaneous tone while all three vasodilators relaxed efferent arterioles with spontaneous tone. The results demonstrate segmental heterogeneity for these vasodilators in the rabbit renal microvasculature, with ACh causing relaxation in all three vessel types, DA acting primarily on the glomerular arterioles, and BK affecting only the efferent arteriole.
Alpha2-adrenoceptors and cellular cAMP levels in single nephron segments from the rat
Authors: Umemura S. , Marver D. , Smyth D. D. , Pettinger W. A.
Published: December 2017

A functional role for the numerically predominant renal alpha2-adrenoceptors, which in other tissues inhibit adenylate cyclase, remains undefined. We therefore examined the effect of alpha2-adrenoceptor stimulation with (-)-epinephrine (E) on cell cAMP content in the isolated proximal convoluted tubule (PCT), medullary and cortical thick ascending limb of Henle, and collecting tubule (MTAL, CTAL, MCT, and CCT, respectively). Parathyroid hormone (1-34 PTH), in PCT or CTAL, or arginine vasopressin (AVP), in MTAL, CTAL, MCT, or CCT, was used to activate adenylate cyclase in intact cells from these microdissected nephron segments in the presence of 3-isobutyl-1-methylxanthine (phosphodiesterase inhibitor) and propranolol. Alpha2-Adrenoceptors were activated using varying concentrations of E (37 degrees C, 2 min). Alpha2-Adrenoceptor activation with E (5 X 10(-7) to 5 X 10(-6) M) suppressed cellular cAMP stimulation by PTH by 35% in PCT and stimulation by AVP in CCT by 50%. This suppression by E in PCT and CCT was inhibited by 5 X 10(-6) M yohimbine or 5 X 10(-7) M phentolamine but not by 5 X 10(-6) M prazosin. E also suppressed cAMP stimulated by AVP in MCT, but it did not suppress the PTH-or AVP-stimulated increase in cellular cAMP in CTAL and MTAL. These studies show that there are alpha2-adrenoceptors in the rat nephron. Activation of these alpha 2-adrenoceptors can inhibit cAMP formation stimulated by PTH in PCT and by AVP in the CCT and MCT but not in the CTAL and MTAL. A pathophysiological role of altered regulation of these receptors is yet to be described.
Sodium-pyrazinoate cotransport in rabbit renal brush border membrane vesicles
Authors: Manganel M. , Roch-Ramel F. , Murer H.
Published: December 2017

Pyrazinoate (PZA) is an organic anion actively reabsorbed and secreted in the mammalian kidney. In experiments with rabbit renal brush border membrane vesicles, we characterized a sodium-PZA cotransport mechanism that could be involved in reabsorption. An inwardly directed sodium gradient stimulated the influx of PZA. The sodium-dependent transport was electroneutral, suggesting a 1:1 stoichiometry. The kinetic constants for sodium-PZA cotransport were measured under initial linear flux and zero trans conditions for both sodium and PZA. The apparent Km for sodium was about 60 mM. At 90 mM sodium the apparent Km for PZA was about 1.1 mM; increasing the sodium concentration augmented the apparent affinity for PZA. Cis inhibition of sodium-dependent PZA uptake was observed by the addition of nicotinate, lactate, probenecid, succinate, beta-hydroxybutyrate, and salicylate. Urate had no effect. [14C]PZA uptake was trans stimulated by PZA itself, lactate, and nicotinate. PZA shares a transport system(s) involved in the proximal tubular reabsorption of these two anions.
Active transport of chloride by lateral ventricle choroid plexus of the rat
Authors: Smith Q. R. , Johanson C. E.
Published: December 2017

The nature of Cl transport and its relation to Na and K transport were analyzed in adult rat lateral ventricle choroid plexus incubated in cerebrospinal fluid (CSF) medium at 37 degrees C and PCO2 = 30 mmHg. In synthetic CSF (extracellular Cl [( Cl]o) = 130 mM), the intracellular Cl [( Cl]i) was three times that estimated for passive distribution. Choroid plexus [Cl]i was not determined by Donnan distribution because [Cl]i remained constant at approximately 50 mM while the [K]i/[K]o ratio was varied 10-fold by drugs and cation substitutions. A [Cl]i/[Cl]o ratio of approximately 0.38 was found when [Cl]o was varied from 15 to 130 mM by isosmotic replacement of Cl with methyl sulfate or isethionate. However, the [Cl]i/[Cl]o ratio increased to greater than 1.0 when [Cl]o was lowered below 5 mM. Reduction in bath temperature to 15 degrees C (CSF PCO2 = 50 mmHg) increased both [Cl]i/[Cl]o and [HCO3]i/[HCO3]o to approximately 0.6. SITS, an inhibitor of Cl-HCO3 transport, reduced [Cl]i by 18 mM, decreasing the [Cl]i/[Cl]o ratio close to the equilibrium value. In contrast, neither furosemide (10(-3) M) nor low CSF [Na]o (3 mM) reduced Cl accumulation. It is concluded that uphill movement of Cl into choroid plexus epithelium occurs primarily by Cl-HCO3 antiport and not by Na-Cl symport.
Renal prostanoids after unclipping the denervated one-kidney, one-clip hypertensive rat
Authors: Vandongen R. , McGowan H. , Anderson H. , Barden A.
Published: December 2017

The contribution of the renal nerves in maintaining blood pressure and modulating renal prostanoid synthesis was examined in established (less than 8 wk in duration) one-kidney, one-clip (1K,1C) hypertension in the rat. Systolic blood pressure was measured for 7 days after renal denervation, at which time the renal artery clip was removed. Twenty-four-hour urinary excretion of PGE2 and 6-keto-PGF1 alpha (stable degradation product of PGI2) was determined before and after denervation and unclipping. Compared with sham-denervated rats, denervation (n = 15) resulted in a small but significant fall in blood pressure (from 216 +/- 4 to 182 +/- 4 mmHg after 48 h) and an increase in urinary 6-keto-PGF1 alpha (from 31 +/- 4 to 43 +/- 5 ng/24 h after 24 h). There was no change in PGE2 excretion. Seven days after surgery, blood pressures were similar in denervated (202 +/- 4 mmHg) and sham-denervated (211 +/- 5 mmHg) rats and fell to a similar extent 24 h after unclipping (142 +/- 3 and 147 +/- 4 mmHg, respectively). Urinary 6-keto-PGF1 alpha increased from 25 +/- 5 to 74 +/- 11 in denervated and 21 +/- 2 to 72 +/- 9 ng/24 h in sham-denervated rats in the 24 h after unclipping. PGE2 excretion increased approximately twofold over this period. These findings indicate that the renal nerves have only a minor role in established hypertension in the 1K,1C rat and that the reversal of hypertension and stimulation of renal prostanoid synthesis following unclipping is not dependent on neural mechanisms.
Effects of calcium antagonists on renal hemodynamics
Authors: Loutzenhiser R. , Epstein M.
Published: December 2017

The renal hemodynamic effects of Ca2+ antagonists are considered in the context of their actions on Ca2+ movements during activation of vascular smooth muscle. Observations in intact animals reveal that the renal hemodynamic response to Ca2+ antagonists is highly variable, depending on the neural and hormonal determinants of renal vascular tone. Studies in the isolated perfused kidney and in isolated renal vessels indicate that diverse agonists use different activating mechanisms with differing sensitivities to Ca2+ antagonists. In comparison with other direct-acting vasodilators, Ca2+ antagonists are unique in their ability to maintain or increase glomerular filtration rate. This effect is due, in part, to their selective reduction of afferent arteriolar resistance. This implies that activating mechanisms of the afferent and efferent arterioles differ. The ability of Ca2+ antagonists to augment glomerular filtration rate by concomitant actions on nonvascular sites remains to be elucidated.
Effect of ADH on chloride reabsorption in the loop of Henle of the Brattleboro rat
Authors: Work J. , Galla J. H. , Booker B. B. , Schafer J. A. , Luke R. G.
Published: December 2017

Both in vivo superficial loop segment microperfusion and in vitro perfusion of isolated medullary thick ascending limb segments were used to assess the effect of vasopressin on loop of Henle chloride absorption in the Brattleboro rat. Superficial loop segments were perfused between the latest proximal and earliest distal tubule in vivo at 19.2 +/- 0.4 nl/min (mean +/- SE) with an artificial tubule fluid. Under control conditions, absolute chloride reabsorption was 1,596 +/- 61 pmol/min and increased to 1,876 +/- 102 after intravenous infusion of vasopressin (P less than 0.005). Distal tubule fluid chloride concentration decreased 4.6 +/- 1.5 meq/liter (P less than 0.05), and fractional chloride reabsorption increased 4.8 +/- 2.0% (P less than 0.05). For in vitro perfusion, medullary thick ascending limb segments were bathed and perfused (9-15 nl/min) with phosphate-buffered solutions at 38 degrees C. Under control conditions, transepithelial voltage was +2.4 +/- 0.3 mV, lumen positive, and the net chloride flux was 147 +/- 24 pmol X min-1 X mm-1 in the absorptive direction. Addition of vasopressin to the bathing solution increased net chloride reabsorption to 342 +/- 56 pmol X min-1 X mm-1 (P less than 0.02) and transepithelial voltage to 3.0 +/- 0.3 mV (P less than 0.002). An additional group of tubules was examined under identical conditions; however, vasopressin was removed from the bathing medium during a subsequent recovery period. In these experiments, net chloride flux and transepithelial voltage significantly increased compared with the control period and returned to control values upon removal of vasopressin from the bath.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of renal ammoniagenesis in the dog with chronic metabolic acidosis: effect of a glutamine load
Authors: Gougoux A. , Vinay P. , Halperin M. L.
Published: December 2017

We recently emphasized that ATP is an obligatory product of renal glutamine metabolism and that all cells must remain in ATP balance. Based on this, we suggested that the maximum rate of renal ammoniagenesis in dogs with chronic metabolic acidosis may be limited by the rate of ATP utilization in the kidney. Since a large infusion of glutamine led to a twofold increase in renal ammoniagenesis in acidotic dogs, we wished to evaluate the renal metabolic changes that permitted this increment within the constraints of renal ATP balance. A large glutamine infusion did not lead to an augmented rate of ATP hydrolysis because renal oxygen consumption was not increased. Two major metabolic changes could explain this stimulation while maintaining ATP balance: first, ATP production from lactate by the kidney was decreased following the glutamine infusion; second, the metabolic fate of glutamine was changed so that more ammonium per ATP was synthesized (i.e., the rates of amino acid release into the renal vein were markedly enhanced, and gluconeogenesis was now a quantitatively significant process). 3-Mercaptopicolinate, an inhibitor of phosphoenolpyruvate carboxykinase, when infused with glutamine, apparently decreased the calculated rate of gluconeogenesis as expected; however, ammonium production did not decline, because the rate of amino acid release increased further, as did the rate of oxygen consumption. Therefore, a large glutamine infusion increased renal ammoniagenesis in dogs with chronic metabolic acidosis while maintaining ATP balance, because ATP production from other substrates was decreased and because the fate of glutamine metabolism was altered in that less ATP was formed per glutamine utilized.
Effect of intrarenal angiotensin II infusion on the renal escape from mineralocorticoid
Authors: Opgenorth T. J. , Granger J. P. , Chakravarthy A. , Knox F. G. , Romero J. C.
Published: December 2017

This study examined the hypothesis that suppression of the antinatriuretic action of angiotensin II (ANG II) is an important determinant of the escape from the sodium-retaining effects of mineralocorticoid. In five uninephrectomized dogs aldosterone (ALDO) infusion (10 ng X kg-1 X min-1) produced a fall in sodium excretion (UNaV) on the first day that returned to control on the fourth day of ALDO infusion. Mean arterial pressure (MAP) increased from 89 +/- 1 to 100 +/- 1 mmHg, and glomerular filtration rate (GFR) increased from 38 +/- 3 to 45 +/- 3 ml/min during ALDO infusion. After recovery, intrarenal infusion of ANG II (1.5 ng X kg-1 X min-1) was initiated to maintain a constant level of ANG II during the subsequent aldosterone administration. The intrarenal ANG II infusion produced a sustained increase in MAP (12 +/- 4 mmHg) and a sustained decrease in GFR (11 +/- 5 ml/min) and effective renal plasma flow (42 +/- 17 ml/min). With intrarenal ANG II levels fixed, ALDO infusion again produced a marked decrease in UNaV on the first day followed by a return to control levels on the third day. Again, MAP and GFR increased significantly during ALDO infusion (from 101 +/- 2 to 119 +/- 2 mmHg and from 27 +/- 6 to 35 +/- 4 ml/min, respectively). The absolute increase in MAP was significantly greater during ALDO infusion with intrarenal ANG II infusion as compared with ALDO infusion with intrarenal vehicle infusion alone.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of intermittent feeding on renal hemodynamics in conscious rats
Authors: Gehrig J. J. , Jamison R. L. , Baylis C. , Troy J. L. , Brenner B. M. , Jamison R. L.
Published: December 2017

The hemodynamic influences of many forms of dietary restriction have not been studied in the conscious rat. To examine the effect of one regimen of dietary restriction, alternate-day feeding, on renal hemodynamics, we performed 56 clearance studies in 20 unanesthetized, previously catheterized male Sprague-Dawley rats at mean age 30 wk. Group 1 rats (n = 10) were given standard chow only on alternate days for 25 wk and then studied after feeding and after fasting days, whereas group 2 rats (n = 10) were fed ad libitum during the same period and then studied randomly. In group 1, glomerular filtration rate (GFR, clearance of inulin) and renal blood flow [RBF, clearance of PAH/(1 - hematocrit)] increased 23 and 19%, respectively, after feeding days compared with fasting days (GFR, 4.25 vs. 3.47 ml/min, P less than 0.005; RBF, 22.2 vs. 18.6 ml/min, P less than 0.025). After feeding, mean arterial pressure and plasma protein concentration were unchanged, hematocrit increased slightly, and fractional excretion of sodium rose from 0.23 to 0.57%. Both GFR and RBF averaged 31% less in group 1 than in group 2 but, when factored by body weight, the differences were abolished. The results indicate that alternate-day feeding causes substantial oscillations in GFR and RBF in healthy awake rats through mechanisms unlikely to involve changes in extracellular fluid volume alone and limits GFR and RBF to average values markedly lower than those observed for larger ad libitum-fed rats of the same age.
Dexamethasone and hydrogen peroxide production by mesangial cells during phagocytosis
Authors: Baud L. , Perez J. , Ardaillou R.
Published: December 2017

We have previously demonstrated that a high percentage of rat cultured mesangial cells phagocytized serum-treated zymosan (STZ) (L. Baud, J. Hagege, J. Sraer, E. Rondeau, J. Perez, and R. Ardaillou, J. Exp. Med. 158: 1836-1852, 1983). Phagocytosis resulted in stimulation of arachidonic acid metabolism with generation of H2O2. Exposure of mesangial cells to dexamethasone for 48 h produced a dose-dependent decrease in phagocytosis-induced production of H2O2 with a 50% inhibitory concentration of 32 nM. The decrease in H2O2 release was associated with the inhibition of prostaglandin (PG) E2 production. The effect of dexamethasone could be considered as due to receptor-mediated modulation of protein synthesis since dexamethasone was not active immediately but only after a lag period of 3 h; RU 38486, a potent competitor for dexamethasone receptors, counteracted the reduction in H2O2 generation; and actinomycin and cycloheximide both blunted the inhibitory effect of dexamethasone. Pretreatment of mesangial cells with dexamethasone also produced a dose-dependent decrease in the phagocytic capability of the cells (63% inhibition for 1 microM dexamethasone). However, the inhibitory effect of dexamethasone on H2O2 production expressed as percentage of control was similar whether or not phagocytosis had been blocked by cytochalasin B. This result and also the fact that dexamethasone inhibited H2O2 production in cells triggered with soluble stimuli (A 23187 ionophore, PAF) suggested that the effect of dexamethasone on H2O2 generation was independent of that on phagocytosis. Addition of exogenous arachidonic acid reduced the effect of dexamethasone only when its conversion into PGE2 was inhibited by indomethacin.(ABSTRACT TRUNCATED AT 250 WORDS)
Atrial natriuretic factor can increase renal solute excretion primarily by raising glomerular filtration
Authors: Cogan M. G.
Published: December 2017

Controversy persists on whether atrial natriuretic factor (ANF) raises renal solute excretion simply by increasing glomerular filtration rate (GFR) or whether it directly inhibits tubular transport (independent of changes in flow rate). Free-flow micropuncture techniques were used in 10 Munich-Wistar rats. ANF caused a significant increase in single-nephron and whole-kidney GFR (41.6 +/- 1.4 to 52.7 +/- 2.3 nl/min and 0.95 +/- 0.05 to 1.24 +/- 0.09 ml/min, respectively). Although absolute proximal sodium, bicarbonate, and chloride reabsorption increased, the increment in reabsorption was less than the increase in load; therefore solute delivery out of the proximal tubule increased by approximately 30-35%. Whole-kidney electrolyte excretion also rose markedly. When single-nephron and whole-kidney GFR were reduced back to a control level by aortic constriction (40.2 +/- 1.8 nl/min and 0.93 +/- 0.05 ml/min, respectively), proximal transport reverted to normal values despite persistent ANF administration. Ninety percent of the ANF-induced natriuresis and chloruresis were simultaneously abolished when GFR was normalized. In conclusion, ANF has no direct effect on reabsorption in the superficial proximal convoluted tubule independent of changes in filtration rate. Although direct effects on more distal or deeper nephron segments are not precluded, the present data suggest that ANF can increase renal solute excretion predominantly by acutely augmenting GFR.
Regulation and function of arginine vasopressin in pregnant sheep
Authors: Bell R. J. , Laurence B. M. , Meehan P. J. , Congiu M. , Scoggins B. A. , Wintour E. M.
Published: December 2017

The aim of this study was to investigate the regulation and function of arginine vasopressin (AVP) in pregnant sheep. The mean plasma osmolality of nonpregnant ewes (298 +/- 1.0 mosmol/kg, n = 8) was not significantly different from that of late pregnant ewes (295 +/- 1.1 mosmol/kg, n = 21). The mean resting plasma [AVP] of nonpregnant ewes (4.1 +/- 0.6 pg/ml,n = 8) was not significantly different from that of pregnant ewes (3.3 +/- 0.3 pg/ml,n = 21). In a series of dehydration experiments it was established that the slope of the function relating log [AVP] to plasma osmolality for pregnant ewes (n = 13) was not significantly different from the slope of the function relating log [AVP] to plasma osmolality for nonpregnant ewes (n = 4). When AVP was infused into water-loaded ewes, a significant decrease in urinary flow rate and free water clearance occurred at an infusion rate of 0.003 microgram/h in both the pregnant (n = 4) and nonpregnant (n = 4) animals. Both groups achieved negative free water clearance at an infusion rate of 0.01 microgram/h. These findings suggest that pregnancy does not alter the relationship between plasma osmolality and plasma [AVP] or the renal responsiveness to AVP in sheep.
Electrophysiology of sodium-coupled transport in proximal renal tubules
Authors: Lang F. , Messner G. , Rehwald W.
Published: December 2017

Effects of sodium-coupled transport on intracellular electrolytes and electrical properties of proximal renal tubule cells are described in this review. Simultaneous with addition of substrate for sodium-coupled transport to luminal perfusates, both cell membranes depolarize. The luminal cell membrane depolarizes due to opening of sodium-cotransport pathways. The depolarization of the peritubular cell membrane during sodium-coupled transport is primarily due to a circular current reentering the lumen via the paracellular pathway. The depolarization leads to a transient decrease of basolateral potassium conductance that in turn amplifies the depolarization. However, within 5-10 min of continued exposure to substrate, potassium conductance increases again, and peritubular cell membrane repolarizes. During depolarization the driving force of peritubular bicarbonate exit is reduced. As a result net alkalinization of the cell prevails despite an increase of intracellular sodium activity, which reduces the driving force for the sodium-hydrogen ion exchanger and would thus have been expected to acidify the cell. No evidence is obtained for regulatory inhibition of sodium-coupled transport by intracellular sodium or calcium. Rather, luminal cotransport is altered by the change of driving forces.
ATP-dependent proton transport in human renal medulla
Authors: Diaz-Diaz F. D. , LaBelle E. F. , Eaton D. C. , DuBose T. D.
Published: December 2017

An electrogenic proton-translocating ATPase (H+-ATPase) has been described in turtle urinary bladder and bovine and rat renal medulla. In the present study, a membrane fraction with ATP-dependent H+ transport activity was isolated from human renal medulla. Intravesicular acidification was assessed by acridine orange absorbance changes. Proton transport was abolished by N-ethylmaleimide but not oligomycin or vanadate, differentiating this H+-ATPase from mitochondrial F0-F1 H+-ATPase and gastric H+-K+-ATPase. In addition, vesicular proton uptake was demonstrated to be independent of sodium and potassium cotransport. Proton translocation rate increased when transmembrane potential was clamped with valinomycin supporting an electrogenic mechanism. Hydrogen ion transport was dependent on the presence of chloride or bromide, since substitution by fluoride or nitrate markedly decreased intravesicular acidification. The transport characteristics of this proton-translocating ATPase are similar to those described for turtle urinary bladder and bovine and rat renal medulla, which have been assumed to play a role in urinary acidification by the medullary collecting duct.
Effect of barium on potassium transport in amphibian kidney
Authors: Zupka M. T. , Sullivan L. P.
Published: December 2017

We have examined the effect of barium on K excretion and transport in the perfused frog kidney. The transepithelial secretory flux of K was calculated from the rate of excretion of 42K from the portal circulation. Barium was applied to the basolateral surfaces of the tubules via the portal circulation. Barium (0.1 mM) increased fractional K excretion from 55 to 178% by stimulating the K secretory flux; 0.5 mM Ba increased fractional K excretion from 39 to 386% primarily by increasing the secretory flux greater than 10-fold. Tissue content increased 10%. When Ba was applied to both the apical and basolateral surfaces by perfusion of the arterial circulation, K excretion and secretion also increased. This same result was obtained when K secretion was first stimulated by acetazolamide. In another series of experiments, tubular cells were loaded with 42K via a pulse injection into the portal circulation, and simultaneous washout of the isotope into the urine and the venous effluent was measured. Analysis of the washout curves revealed that basolateral (portal) application of Ba inhibited efflux of K from the cells into the circulation, reduced the influx from the circulation, and stimulated efflux into the urine. We suggest that blockade of K channels in the basolateral membrane indirectly depolarizes the apical membrane and thereby increases the electrochemical gradient favoring K movement from cells to tubular fluid. When Ba is applied simultaneously to both tubular surfaces, the effect on the basolateral surface apparently overrides any direct effect it may have on K movement across the apical surface. Using 133Ba, we measured a very small transepithelial perfusate-to-tubular fluid flux. However, fractional Ba reabsorption averaged 19% when 0.5 mM Ba was present in the arterial perfusate.
Glomerular capillary permeability in developing canines
Authors: Goldsmith D. I. , Jodorkovsky R. A. , Sherwinter J. , Kleeman S. R. , Spitzer A.
Published: December 2017

The changes in glomerular permeability that occur during development were assessed in 1- and 6-wk-old canines by analyzing dextran-sieving curves obtained in six animals at each age. The fractional clearance of the smallest dextran molecules (18 A) was 0.97 +/- 0.02 (+/- SE) in both 1- and 6-wk-old animals, and it became progressively less at larger molecular sizes. The sieving curves were consistent with an isosporous model of a glomerular capillary. When axial changes in protein concentration were included in the mathematical model, the apparent pore radius was 62.7 +/- 1.7 and 61.7 +/- 1.69 A in 1- and 6-wk-old puppies, respectively (P greater than 0.7). The effects of developmental changes in hydrostatic pressure and renal blood flow were balanced by the increases in serum protein concentration and filtration fraction leaving the fractional clearances of macromolecules unchanged. In contrast, the total cross-sectional pore area per unit path length (Aw/delta x) increased during this 6-wk period by approximately 7.5-fold (from 1.39 +/- 0.2 to 10.55 +/- 3.0 10(-5) cm, P less than 0.0001), and the ultrafiltration coefficient rose from 0.012 +/- 0.002 to 0.093 +/- 0.012 ml X s-1 X mmHg-1 (P less than 0.0001). The findings reveal constancy of pore size and an increase in total pore area as a function of age. Analysis by classical pore theory yielded similar findings. We conclude that the predominant factor determining the rise in glomerular filtration rate during development is the large increment in Aw/delta x, which in turn is due to increases in the surface area and pore density of the glomerular capillaries.
Reactive oxygen species: production and role in the kidney
Authors: Baud L. , Ardaillou R.
Published: December 2017

Reactive oxygen species (ROS) are formed by incomplete reduction of molecular oxygen. They include superoxide anion (O2-.), hydrogen peroxide (H2O2), hydroxyl radical (OH.), and singlet oxygen (1O2). ROS may induce different types of cell injury, particularly lipid peroxidation and membrane damage. ROS have been shown to play an essential role in the mechanisms of experimental models of several renal diseases: ischemic acute renal failure, renal graft rejection, acute glomerulonephritis, and toxic renal diseases. They are produced by the renal cells and also by the inflammatory bone marrow-derived cells invading the renal tissue. ROS, regardless of their origin, may degrade the glomerular basement membrane and alter the glomerular and tubular cell functions. Particularly, they produce an increase in cyclic AMP synthesis and prostaglandin production in the glomeruli. Recent studies have shown that the glomerular mesangial cells themselves generated ROS on stimulation by phagocytosis of foreign particles or exposure to the complement membrane attack complex or platelet-activating factor. Production of ROS is in narrow relationship with the metabolism of arachidonic acid. Conversion of this fatty acid via the lipoxygenase pathway is associated with an increase of ROS, whereas its transformation into prostaglandins via the cyclooxygenase pathway results in the opposite effect. Production of ROS in activated mesangial cells can be inhibited by glucocorticoids via a receptor-mediated mechanism. The fact that some of these characteristics are different in leukocytes suggests the possibility in the future of the more specific pharmacological control of the inflammatory process in the glomerular mesangium.
31P-NMR in vivo measurement of renal intracellular pH: effects of acidosis and K+ depletion in rats
Authors: Adam W. R. , Koretsky A. P. , Weiner M. W.
Published: December 2017

Renal intracellular pH (pHi) was measured in vivo from the chemical shift (sigma) of inorganic phosphate (Pi), obtained by 31P-nuclear magnetic resonance spectroscopy (NMR). pH was calculated from the difference between sigma Pi and sigma alpha-ATP. Changes of sigma Pi closely correlated with changes of sigma monophosphoesters; this supports the hypothesis that the pH determined from sigma Pi represents pHi. Renal pH in control rats was 7.39 +/- 0.04 (n = 8). This is higher than pHi of muscle and brain in vivo, suggesting that renal Na-H antiporter activity raises renal pHi. To examine the relationship between renal pH and ammoniagenesis, rats were subjected to acute (less than 24 h) and chronic (4-7 days) metabolic acidosis, acute (20 min) and chronic (6-8 days) respiratory acidosis, and dietary potassium depletion (7-21 days). Acute metabolic and respiratory acidosis produced acidification of renal pHi. Chronic metabolic acidosis (arterial blood pH, 7.26 +/- 0.02) lowered renal pHi to 7.30 +/- 0.02, but chronic respiratory acidosis (arterial blood pH, 7.30 +/- 0.05) was not associated with renal acidosis (pH, 7.40 +/- 0.04). At a similar level of blood pH, pHi was higher in chronic metabolic acidosis than in acute metabolic acidosis, suggesting an adaptive process that raises pHi. Potassium depletion (arterial blood pH, 7.44 +/- 0.05) was associated with a marked renal acidosis (renal pH, 7.17 +/- 0.02). There was a direct relationship between renal pH and cardiac K+. Rapid partial repletion with KCl (1 mmol) significantly increased renal pHi from 7.14 +/- 0.03 to 7.31 +/- 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of reduction in renal artery pressure on atrial natriuretic peptide-induced natriuresis
Authors: Davis C. L. , Briggs J. P.
Published: December 2017

Studies were undertaken in anesthetized male Sprague-Dawley rats to investigate the effects of lowering renal arterial pressure within the autoregulatory range (to 85-95 mmHg) on the renal response to atriopeptin II (AP II) and atrial extract (AE). The natriuresis and diuresis produced by bolus injections of AP II at three dose levels (250-1,000 ng) was abolished or substantially reduced at lowered arterial pressure (85 mmHg). When renal artery pressure was lowered at the same time as an AE infusion was begun it completely blocked the natriuresis and diuresis. When pressure was reduced after 45 min of AE infusion the natriuresis was blunted, but not fully abolished. The effect of prior reduction in renal arterial pressure on the response to AP II (100 ng/min) and furosemide was compared; the AP II natriuresis was prevented when arterial pressure was lowered to 90 mmHg, but the natriuretic effect of furosemide was only slightly diminished. There was no significant rise in glomerular filtration rate (GFR) with AP II and no correlation between GFR changes and the Na excretory response. Reducing renal arterial pressure prior to, at the same time as, or 45 min after beginning an infusion of atrial natriuretic peptide substantially blunts or completely abolishes the natriuresis. Reductions in renal arterial pressure may block the natriuretic and diuretic effects of these compounds by interfering with their hemodynamic actions or by causing sufficient enhancement of salt reabsorption to limit delivery to terminal nephron segments.
Renal metabolism of amino acids in vivo: studies on serine and glycine fluxes
Authors: Lowry M. , Hall D. E. , Hall M. S. , Brosnan J. T.
Published: December 2017

The pathway of serine synthesis by the rat kidney has been investigated in vivo by measuring the net flux in the presence and absence of specific inhibitors of the glycine cleavage system, phosphoenol-pyruvate carboxykinase and gamma-glutamyltranspeptidase. In normal animals serine release was 705 +/- 187 nmol X min-1 X animal-1, whereas glycine uptake was only 28% of this value. Inhibition of the glycine cleavage system (cysteamine infusion) resulted in a reversal of glycine flux with no change in serine production. In similar experiments with mercaptopicolinate serine release was decreased by 55% with no change in glycine removal. AT-125, a potent inhibitor of gamma-glutamyltranspeptidase, had no effect on renal serine and glycine fluxes. In chronically acidotic rats serine synthesis was unchanged, but there were significant increases in the uptake of glutamine (fourfold) and glycine (2.5-fold). Infusion of cysteamine into these animals caused a 50% decrease in serine release with a significant reversal of the glycine flux. Infusion of mercaptopicolinate had effects similar to those observed in normal animals. These results show that renal serine synthesis can occur by both the phosphorylated-intermediate pathway and serine hydroxymethyltransferase in vivo. Furthermore, they demonstrate that glycine can contribute significantly to ammoniagenesis during acidosis.
N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline, amiloride analogues, and renal Na+/H+ antiporter
Authors: Rocco V. K. , Cragoe E. J. , Warnock D. G.
Published: December 2017

N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) is a carboxyl-activating agent and has been shown to inhibit the renal Na+/H+ antiporter. The purposes of the present studies were to characterize the kinetics of inhibition of the Na+/H+ antiporter by EEDQ and to determine whether amiloride analogues affect the ability of EEDQ to inhibit the rate of Na+/H+ exchange. Brush-border membrane vesicles (BBMV) were prepared from rabbit kidneys; Na+/H+ exchange rate was assessed by the fluorescence quenching of acridine orange. EEDQ produced a concentration-dependent inhibition of Na+/H+ exchange; the effect was to decrease the maximum activity (Vmax) from 5.51 to 2.03 fluorescence units X mg protein-1 X S-1) and Km (from 14.1 to 8.7 mM) compared with control BBMV. Pretreatment of BBMV with amiloride before the addition of EEDQ maintained both Vmax and Km at values that were not significantly different from those for control BBMV. Compared with a series of analogues, amiloride was only the third most potent inhibitor of the rabbit renal Na+/H+ antiporter; amiloride, however, provided the greatest protection against inhibition of the antiporter by the subsequent addition of EEDQ. These findings suggest that the 2-carbonylguanidininum moiety and 6-chloro atom are important for binding of amiloride to sites at or near the antiporter; the group at position 5 is important in determining the ability of amiloride to protect against inhibition of the Na+/H+ antiporter by EEDQ. Finally, the ability of amiloride to protect against inactivation of the renal Na+/H+ antiporter by EEDQ is reversible.
Ionic permeabilities of rat renal cortical brush-border membrane vesicles
Authors: Lipkowitz M. S. , Abramson R. G.
Published: December 2017

It is generally assumed that electrolytes equilibrate readily across renal cortical brush-border membrane vesicles (BBMV). This assumption was tested by use of two new methods in rat BBMV prepared with free-flow electrophoresis (FFE), Mg aggregation, or Ca aggregation. Intravesicular KCl and RbCl concentrations, as well as the conductance of Cl relative to K (GCl/GK) and GNa/GK were determined with the fluorescent, potential-sensitive probe 3,3'-dipropylthiadicarbocyanine iodide [diS-C3-(5)]; intravesicular KCl concentration was also approximated utilizing the response of Na-dependent [3H]glucose uptake to variations in the membrane potential. These studies demonstrated that KCl fails to attain electrochemical equilibrium in BBMV prepared by the three methods, despite prolonged incubation at 22 degrees C; a significant, inwardly directed electrolyte gradient was sustained in all cases. The intravesicular electrolyte concentration was lower in BBMV prepared with FFE than in those prepared with Mg or Ca. GCl/GK was lowest in BBMV prepared with FFE and highest in those prepared with Ca; GNa/GK was comparable in all preparations. The apparent impermeance of BBMV may impact significantly in interpreting data from studies that require knowledge of the precise concentration of intravesicular electrolytes.
Improved separation method for rat proximal and distal renal tubules
Authors: Gesek F. A. , Wolff D. W. , Strandhoy J. W.
Published: December 2017

We modified and improved enzyme digestion and density gradient separation procedures to obtain fractions of proximal and distal renal tubules with high yield and viability. Kidneys from two anesthetized adult Wistar rats were flushed with Krebs-Henseleit buffer (KHB) and then perfused in situ with recirculated KHB containing collagenase and hyaluronidase at 125 mmHg. Cortices were excised, minced, and incubated in KHB containing enzymes for 35 min at 37 degrees C. Dissociated tubules were removed at 10-min intervals, rinsed, and placed in KHB containing 10% calf serum, vitamins, and amino acids at 4 degrees C. Separation was achieved by suspending the tissue in 45% isosmotic Percoll layered over an undiluted Percoll cushion and centrifuging. Proximal tubules sedimented near the cushion. Distal segments were isolated in the uppermost bands of a second 35% Percoll separation. Viability was greater than 95% as measured by lactate dehydrogenase leakage and quantitated by oxygen consumption and ATP content. Basal oxygen consumption was greater than 33 nmol O2 X min-1 X mg protein-1 in all fractions and was stimulated by succinate and inhibited by amiloride and ouabain. Basal ATP content averaged 9.7 nmol/mg ATP. An average 3.3-fold separation for the proximal fraction and 24.5-fold separation for the distal fraction was assessed by the enrichment of six specific enzyme markers, with several of the markers indicating separations up to 32-fold. Isolated tubules also displayed functional responses to parathyroid hormone and vasopressin. Distal, but not proximal, segments demonstrated significantly increased adenosine 3',5'-cyclic monophosphate formation with vasopressin.
Postglomerular capillary solute flux restricted by shape and charge in the dog
Authors: Whiteside C. , Silverman M.
Published: December 2017

The permselectivity characteristics of the postglomerular (PG) microcirculation in dog kidney were investigated employing 3H-labeled cationic (DEAE) and anionic sulfated dextrans (dextran-SO4) ranging from 19 to 29 A Stokes-Einstein Radius. With the use of the multiple-indicator dilution (MID) technique, a bolus injection was made into the left renal artery and timed serial samples were obtained from renal venous and urine outflows. The injection solution contained 125I-labeled albumin (plasma reference), [14C]inulin and/or creatinine (glomerular and interstitial references), and a test [3H]dextran probe. A control run was carried out with tracer, then charge interaction was analyzed by repeating the MID run with excess unlabeled compound or after protamine sulfate infusion. After loading, renal vein recovery and mean transit time (t) were unchanged relative to [14C]inulin for [3H]dextran-SO4. But excess DEAE resulted in reduced recovery and decreased t for [3H]DEAE. After protamine sulfate, the renal vein and urine recoveries of [3H]dextran-SO4 decreased and the renal vein t increased. These findings demonstrate saturable anionic binding sites in the PG microcirculation. Under conditions where charge interaction was eliminated, the ratio of renal vein t for 125I-albumin to cationic or anionic dextran was always less than its ratio to neutral dextran, implying a larger apparent volume of distribution. We concluded that PG capillaries also limit solute flux on the basis of shape.