bluuebunny/crossref_metadata_2025 huggingface dataset:
Sex differences in autoregulation of juxtamedullary glomerular blood flow in hydronephrotic rats
Authors: Steinhausen M. , Ballantyne D. , Fretschner M. , Parekh N.
Published: December 2017

The technique of the split hydronephrotic kidney of anesthetized Wistar rats was used for the first time to study afferent and efferent arterioles of juxtamedullary (JM) glomeruli in vivo and to compare their behavior with that of the cortical glomeruli in female (F, 270 g body wt) and male (M, 400 g body wt) rats. The mean length of cortical efferent arterioles (F, 260; M, 380 microns) was less than 10% the length of JM efferent arterioles. Luminal diameters of the JM afferent arteriole (F, 17.1; M, 18.3 microns) and efferent arteriole (F, 25; M, 33.4 microns) were much larger than those of cortical arterioles (afferent: F, 9.1, M, 10.5 microns; efferent: F and M, 11.1 microns). In the hydronephrotic kidney, cortical glomerular blood flow (F, 17.5; M, 18.3 nl/min) is much reduced compared with the normal filtering kidney. This, however, is not true of JM glomerular blood flow (F, 120; M, 262 nl/min). During the reduction of renal perfusion pressure in females blood flow was autoregulated in cortical glomeruli within the pressure range of 110 to 80 mmHg; JM glomeruli failed to show any autoregulation. In males the glomerular blood flow was similarly autoregulated down to 90 mmHg in both cortical and JM nephrons. Local application of indomethacin to the kidneys from female rats reduced the glomerular flow rates by 30% but changed the autoregulatory behavior of cortical and JM glomerular blood flow so that it resembled that observed in untreated males. The data suggest that in females the autoregulatory response, particularly in JM glomeruli, is modified by prostaglandins.
Renal hemodynamic and natriuretic effects of manganese and interactions with atrial natriuretic peptide
Authors: Lafferty H. M. , Gunning M. , Brady H. R. , Brenner B. M. , Anderson S.
Published: December 2017

Manganese (Mn2+) is a cofactor for guanylate cyclase (GC), which is involved in the generation of guanosine 3',5'-cyclic monophosphate (cGMP), a second messenger for atrial natriuretic peptide (ANP) action. Mn2+ is also, however, a nonselective calcium-channel blocker. We examined the effects of infusion of MnCl2 into normal rats and its interaction in vivo and in vitro with GC and ANP. MnCl2 significantly increased glomerular filtration rate (GFR) and effective renal plasma flow rate (RPF). These effects were caused by selective afferent arteriolar vasodilatation, which allowed the glomerular capillary plasma flow rate and hydraulic pressure to rise, thus elevating single-nephron GFR. Urinary Na+ excretion (UNaV) also increased with MnCl2. The natriuresis was, unlike ANP, not mediated by GC activation and cGMP production, as MnCl2 had no effect on either urinary cGMP excretion or cGMP accumulation in intact inner medullary collecting duct cell (IMCD) suspensions, nor did it affect Na(+)-dependent oxygen consumption in these cells. When superimposed on an infusion of ANP, MnCl2 resulted in significant increases in UNaV, GFR, and RPF. These effects were associated with small but significant increments in urinary cGMP excretion. However, MnCl2 did not affect in vitro cGMP production in intact IMCDs or glomeruli in response to ANP stimulation. It is uncertain therefore whether the in vivo augmentation of the natriuretic effect of ANP by MnCl2 is related to GC activation and cGMP production.
Isoproterenol increases Ca, Mg, and NaCl reabsorption in mouse thick ascending limb
Authors: Bailly C. , Imbert-Teboul M. , Roinel N. , Amiel C.
Published: December 2017

The effect of isoproterenol (Iso) on tubular transport in the thick ascending limb of Henle's loop (TAL) was investigated by in vitro microperfusion of MTAL (medullary) and CTAL (cortical) from White Swiss mouse kidney. The pattern of activation of adenylate cyclase along the distal tubule was investigated in this strain: results indicated that Iso stimulated adenylate cyclase fivefold in MTAL and ninefold in CTAL. Data from microperfusion experiments showed that Iso (10(-7) M in the bath) significantly and reversibly increased Ca and Mg reabsorption in CTAL. No net transport of Ca and Mg was observed in MTAL whether Iso was present or not. With regard to Na and Cl, Iso significantly stimulated their reabsorption in both segments and increased the transepithelial voltage in MTAL. Iso abolished K reabsorption in MTAL and induced a net K secretion in CTAL, the latter effect being also observed with 10(-9) M of Iso. When applied on CTAL, propranolol (10(-6) M in the bath) inhibited all these effects. These data indicate that beta-adrenergic agonists are involved in the multihormonal modulation of the TAL function.
Adaptation of HCO-3 and NH+4 transport in rat MTAL: effects of chronic metabolic acidosis and Na+ intake
Authors: Good D. W.
Published: December 2017

In vitro microperfusion experiments were performed to determine whether chronic metabolic acidosis or chronic alterations in sodium intake cause adaptive changes in bicarbonate or ammonium transport in the medullary thick ascending limb (MTAL) of the rat. In all experiments, MTAL were studied under standard conditions in vitro with 25 mM bicarbonate in perfusate and bath. Thus changes in transport rates reflect adaptive changes in the intrinsic transport properties of the tubule cells. Chronic metabolic acidosis (induced by oral NH4Cl loading) increased MTAL bicarbonate absorption by 53% and increased net ammonium absorption by 36%. Chronic administration of NaHCO3 (0.28 M NaHCO3 drinking H2O) increased MTAL bicarbonate absorption by 50% and increased net ammonium absorption by 54%, despite systemic metabolic alkalosis. Chronic administration of NaCl (0.28 M NaCl drinking H2O) also increased bicarbonate absorption by 50%. Thus an increase in sodium intake stimulated bicarbonate absorptive capacity to a similar extent when sodium was administered with either chloride or bicarbonate. Moderate dietary sodium restriction (0.5% NaCl) reduced bicarbonate absorption by 20% compared with pair-fed sodium-replete controls (2.2% NaCl). These results demonstrate that 1) the MTAL is a site of regulation of renal acid-base transport, 2) chronic metabolic acidosis is associated with adaptive increases in MTAL bicarbonate and ammonium absorption, changes that are appropriate to correct the acidosis, and 3) dietary sodium intake is an important determinant of MTAL bicarbonate and ammonium transport capacity. The response of the MTAL to changes in sodium intake suggests that this segment may play an important role in maintaining acid-base balance when NaCl intake is altered.
Na(+)-H+ exchange in choroid plexus and CSF in acute metabolic acidosis or alkalosis
Authors: Murphy V. A. , Johanson C. E.
Published: December 2017

Basolateral Na(+)-H+ exchange was analyzed with an in vivo model of choroid plexus (CP) epithelium in nephrectomized adult rats anesthetized with ketamine. Acid-base balance in blood was altered for 1 h over a pH continuum of 7.19 to 7.53 by equimolar intraperitoneal injections of HCl, NH4Cl, NaCl, or NaHCO3. Compartmental analysis enabled determination of CP intracellular pH (pHi) [dimethadione (DMO) method] and the choroid cellular concentration of 23Na (stable) and 22Na (tracer). HCl acidosis reduced the outwardly directed transmembrane basolateral H+ gradient, lowered the [23Na]i by 25%, and decreased the influx coefficient (Kin) for 22Na from blood into CP parenchyma (by 45% from 0.211 to 0.117 ml.g-1.h-1) and into cerebrospinal fluid (CSF) (by 43%, from 0.897 to 0.516). Compared with acid-loaded rats (HCl or NH4Cl), the NaHCO3-alkalotic animals had significantly enhanced uptake of 22Na into the CP-CSF system. This pH-dependent transport of Na+ from blood to CP was abolished by pretreatment with amiloride, an inhibitor of Na(+)-H+ exchange. Except in severe acidosis (HCl), the choroid cell pHi (7.05 +/- 0.02 in NaCl controls) and [HCO3-] (11-12 mM) remained stable in the face of acidemic and alkalemic challenges. With respect to reaction of the blood-CSF barrier to plasma acid-base perturbations, the responses of the fourth ventricle plexus pHi, [Na+]i, and 22Na uptake were similar to corresponding ones in lateral plexuses. We conclude that in the choroidal epithelium there is a Na(+)-H+ exchange activity capable of modulating Na+ flux into the CSF by approximately 50% as arterial pH is varied from 7.2 to 7.5.
Glutathione catabolism by the ischemic rat kidney
Authors: Slusser Stephen O. , Grotyohann Lee W. , Martin Louis F. , Scaduto Russell C.
Published: December 2017

The glutathione (GSH) content of rat kidney decreases after cessation of blood flow, falling to 40% of control levels 35 min after renal artery occlusion [R. C. Scaduto, Jr., V. H. Gattone II, L. W. Grotyohann, J. Wertz, and L. F. Martin. Am. J. Physiol. 255 ( Renal Fluid Electrolyte Physiol. 24): F911-F921, 1988]. Renal GSH levels remained depressed for at least 2 h after resumption of blood flow. Because GSH functions in the removal of free radicals, and lipid peroxidation is a free radical-initiated process that occurs in the ischemic kidney, we investigated the fate of this GSH pool in the ischemic kidney. Using high-performance liquid chromatography to measure thiols, we found the loss of GSH to be associated with a stoichiometric accumulation of cysteine in the kidney. Moreover, preischemic labeling of the renal GSH pool with 35S led to accumulation of [35S]cysteine during ischemia that had the same specific activity as that of tissue GSH. Formation of cysteine during ischemia was suppressed in rats pretreated with acivicin, an inhibitor of ɣ-glutamyltransferase (ɣ-GT), although the degree of suppression was small in comparison to the extent of ɣ-GT inhibition. During the initial 2 min of blood reflow after ischemia, tissue cysteine returned to control levels, and a transient increase in the cysteine content of renal venous blood was observed. After ischemia, renal GSH levels remained depressed, but postischemic GSH levels could be increased by administration of N-acetylcysteine during the ischemic period. We conclude that renal ischemia leads to marked catabolism of GSH to cysteine, which is flushed from the tissue upon resumption of renal blood flow. The data are consistent with a pathway involving initial hydrolysis of GSH by ɣ-GT under conditions in which GSH synthesis is suppressed. Resynthesis of GSH after ischemia is limited by the availability of cysteine.

ischemia; cysteine; plasma thiols; kidney thiols

Submitted on August 7, 1989

Accepted on November 20, 1989
Insulin stimulates phosphate transport in opossum kidney epithelial cells
Authors: Abraham M. I. , McAteer J. A. , Kempson S. A.
Published: December 2017

Insulin is antiphosphaturic in vivo and this effect is due, in part, to increased Na(+)-dependent phosphate uptake across the luminal brush-border membrane of the proximal tubule. The intracellular mechanism is not understood. The present study shows that the stimulatory effect of insulin on phosphate transport can be reproduced in opossum kidney (OK) cells, suggesting that this established renal epithelial cell line may be a good model for further studies on insulin action on renal phosphate transport. The stimulation by insulin was dose related when insulin was used at concentrations within the range of 10(-14) to 10(-8) M. At 10(-8) M, insulin had no effect on Na(+)-independent uptake of phosphate or on the Na(+)-dependent uptakes of methyl-alpha-D-glucopyranoside and glutamate. The onset of insulin action on phosphate uptake was detected within 15 min, and the stimulation was reversed completely within 30 min after removal of insulin from the medium. Insulin action was not blocked by protein synthesis inhibitors and was not altered by bacitracin, an inhibitor of intracellular degradation of insulin. Pretreatment with the calcium-channel blockers, nifedipine and verapamil (10(-4) M), produced significant increases in the stimulatory effect of insulin, suggesting indirectly that insulin action on phosphate uptake may be influenced by Ca2+. In contrast to in vivo studies, there was no evidence that insulin interfered with parathyroid hormone action on OK cells.
Differences in synergistic actions of vasopressin and deoxycorticosterone in rat and rabbit CCD
Authors: Chen L. , Williams S. K. , Schafer J. A.
Published: December 2017

We examined the time course of changes in osmotic water permeability (Pf, micron/s), lumen-to-bath 22Na+ flux (Jl----b, pmol.min-1.mm-1), and transepithelial voltage (VT, mV) in response to arginine vasopressin (AVP) in isolated perfused rat and rabbit cortical collecting ducts (CCD). CCDs were isolated from “normal” (untreated) animals and animals 4-14 days after an intramuscular depot injection of deoxycorticosterone pivalate (DOC; 35 mg/rabbit, 5 mg/rat). In the normal rat CCD, 220 pM AVP added to the bathing solution increased Pf from approximately 0 to 981 +/- 120, Jl----b from 24 +/- 5 to 62 +/- 9, and VT from -0.7 +/- 0.6 to -4.0 +/- 0.6 (mean +/- SE; P less than 0.05). The effect of AVP on Pf in DOC-treated rats was not significantly different, but the effects on Jl----b and VT were greater. Jl----b rose from a control value of 78 +/- 16 to 192 +/- 14 with AVP, and VT hyperpolarized from -4.2 +/- 1.6 to -12.2 +/- 0.4. All of these effects of AVP in the normal and DOC-treated rat CCD persisted for greater than or equal to 90-150 min. In DOC-treated rabbit tubules, AVP caused a stable increase in Pf from 9 +/- 6 to 800 +/- 199, which was significantly greater than in normal tubules (379 +/- 32). In the normal rabbit CCD we confirmed previous observations that AVP produces only a transient increase in Na+ absorption and VT; Jl----b increased from 76 +/- 4 to 96 +/- 7 during the period 15-25 min after AVP addition but subsequently fell to 80 +/- 6; VT transiently hyperpolarized from -55 +/- 7 to -64 +/- 8 at 3-8 min after AVP and then fell to -54 +/- 9. In DOC-treated rabbit CCDs, AVP produced no change whatsoever in Jl----b, which was not significantly different from the control value of 99 +/- 7, nor in VT, which was -68 +/- 8 mV. These results indicate fundamental differences in the response of the rat and rabbit CCD to AVP and the presence or absence of synergistic interactions with mineralocorticoids, which may relate to their differing response to other autacoids.
Bulk isolation of renal PCT and PST. II. Differential responses to anoxia or hypoxia
Authors: Ruegg C. E. , Mandel L. J.
Published: December 2017

Innate biochemical responses of rabbit renal proximal convoluted (PCT) and straight (PST) segments following in vitro exposure to anoxia or hypoxia were investigated to delineate the mechanisms responsible for segment-selective injury in vivo. After bulk isolation, suspensions (1 mg/ml) enriched in either PCT or PST were preincubated in Dulbecco's modified Eagle's-Ham's F-12 medium for 1 h before being exposed to either 40 min of anoxia (N2) or 120 min of hypoxia (1% O2) and 1 h of recovery under air-CO2 conditions. After recovery from anoxia, the percent of control values for each viability indicator in PCT and PST, respectively, were as follows: O2 consumption (QO2), 30/50; ATP content, 22/49; K+ content, 60/70; and percent lactate dehydrogenase (LDH) release, 66/45. Likewise, following recovery from hypoxia, the percent of control values for PCT and PST, respectively, were as follows: QO2, 50/90; ATP, 16/57; K+, 52/79; LDH, 45/17. These differential responses indicate that PCT segments were innately more susceptible to anoxic and hypoxic injury than PST segments. Because ATP content was significantly higher in PST segments immediately after anoxia and hypoxia, we investigated glucose-dependent responses during anoxia by exposing these segments to 30 min of anoxia in nutrient buffer with or without glucose. Results from these experiments demonstrate that the PST protection from anoxia was glucose dependent because removal of glucose from the nutrient buffers during anoxia abolishes the differential responses between PCT and PST. The in vitro PCT sensitivity observed here contrasts with the PST sensitivity observed following in vivo ischemia, suggesting that hemodynamic factors present in vivo may ultimately determine the overall susceptibility of PST segments in situ.
Role of angiotensin II in glomerulotubular balance
Authors: Liu F. Y. , Cogan M. G.
Published: December 2017

Inhibition of angiotensin II activity reduces reabsorption of both bicarbonate and chloride predominantly in the S1 subsegment of the proximal convoluted tubule (PCT). Because the S2 PCT is intrinsically better able to compensate for the increased delivery of bicarbonate compared with chloride under normal conditions, we reasoned that angiotensin II inhibition might selectively raise the amount of sodium chloride emerging from the PCT. Free-flow micropuncture techniques were used in normal and alkalotic Munich-Wistar rats that were euvolemic or plasma volume depleted. In the normal volume-depleted animals, saralasin caused a small rise in single-nephron glomerular filtration rate (29.5 +/- 0.6 to 31.5 +/- 0.6 nl/min, P less than 0.025) and fall in bicarbonate and chloride reabsorption in the 1st mm (S1) PCT (387 +/- 22 to 348 +/- 23 peq.mm-1.min-1, P less than 0.05, and 341 +/- 27 to 217 +/- 57 peq.mm-1.min-1, P less than 0.05, respectively). Reabsorptive compensation by the S2 PCT maintained the end-PCT delivery of bicarbonate unchanged (76 +/- 4 to 78 +/- 3 peq.mm-1.min-1, NS), but end-PCT chloride delivery increased significantly (2,014 +/- 41 to 2,248 +/- 29 peq.mm-1.min-1, P less than 0.01). Early distal convoluted tubule (DCT) and urinary bicarbonate excretion were unchanged, but DCT chloride delivery increased associated with a chloruresis. When metabolic alkalosis was present, however, S2 compensation for increased bicarbonate delivery was attenuated so that end-PCT, DCT, and urinary bicarbonate as well as chloride delivery rates increased.(ABSTRACT TRUNCATED AT 250 WORDS)
The vasopressin-regulated urea transporter in renal inner medullary collecting duct
Authors: Knepper M. A. , Star R. A.
Published: December 2017

The terminal part of the inner medullary collecting duct (terminal IMCD) is unique among collecting duct segments in part because its permeability to urea is regulated by vasopressin. The urea permeability can rise to extremely high levels (greater than 100 x 10(-5) cm/s) in response to vasopressin. Recent studies in isolated perfused IMCD segments have established that the rapid movement of urea across the tubule epithelium occurs via a specialized urea transporter, presumably an intrinsic membrane protein, present in both the apical and basolateral membranes. This urea transporter has properties similar to those of the urea transporters in mammalian erythrocytes and in toad urinary bladder, namely, inhibition by phloretin, inhibition by urea analogues, saturation kinetics in equilibrium-exchange experiments, and regulation by vasopressin. The urea transport pathway is distinct from and independent of the vasopressin-regulated water channel. The increase in transepithelial urea transport in response to vasopressin is mediated by adenosine 3',5'-cyclic monophosphate and is associated with an increase in the urea permeability of the apical membrane. However, little is known about the physical events associated with the activation or insertion of urea transporters in the apical membrane. Because of the importance of this transporter to the urinary concentrating mechanism, efforts toward understanding its molecular structure and the molecular basis of its regulation appear to be justified.
Growth hormone stimulates IGF I gene expression in isolated rat renal collecting duct
Authors: Rogers S. A. , Miller S. B. , Hammerman M. R.
Published: December 2017

To determine whether growth hormone (GH) directly stimulates insulin-like growth factor I (IGF I) gene expression in renal collecting duct, plasma membranes prepared from collecting ducts isolated from rat kidney, and collecting ducts themselves were incubated in presence and absence of GH. GH enhanced phospholipase C activity in collecting duct plasma membranes establishing the potential for GH-signal transduction. Inclusion of GH in suspensions of collecting ducts increased production of immunoreactive IGF I in a time-dependent and concentration-dependent manner. Production was stimulated significantly by addition of 10(-10), 10(-8), or 10(-6) M GH to suspensions for 2 h. IGF I produced in isolated collecting ducts was released into the suspending media. Levels of IGF I mRNA in collecting ducts were increased 2.8-fold after incubation with 10(-6) M GH in vitro. IGF I of collecting duct origin was indistinguishable from recombinant human IGF I in terms of its size and receptor-binding characteristics. Our findings demonstrate a direct action of GH to enhance collecting duct IGF I gene expression in vitro. Such enhancement is likely to reflect the mechanism by which GH stimulates renal IGF I production in intact kidney.
Monoaminergic innervation of the rat kidney: a quantitative study
Authors: Barajas L. , Powers K.
Published: December 2017

The sympathetic innervation of the renal tubules and vasculature was characterized by measuring the overlap of accumulations of autoradiographic grains (AAGs) on these structures in autoradiograms of kidney sections from rats injected with tritiated norepinephrine. AAG overlap was used as an indirect measure of the innervation of those structures. The renal vasculature showed x 4.5 more AAG overlap than observed on renal tubules. The greatest amount of AAG overlap occurred on afferent arterioles, followed by efferent arterioles, interlobular arteries, cortical capillaries, arcuate arteries, and renal veins. High concentration of AAGs occurred along the vascular bundles of the outer stripe. In the tubular nephron the proximal tubule had the greatest amount of AAG overlap, followed by the cortical thick ascending limb of Henle, the connecting tubule, the distal convoluted tubule, and the collecting duct. It was found that afferent arterioles had significantly higher mean density of AAG overlap than efferent arterioles for the superficial, midcortical, and juxtamedullary (vascular bundles excluded) renal cortex. There was consistently more AAG perimeter facing the interstitium than overlapping the vasculature. These observations, together with the ultrastructural distribution of synaptic vesicles in varicosities, suggest that the interstitium might be an additional pathway of neurotransmitter access to the effector structures.
Glucose absorption by isolated perfused rat proximal straight tubules
Authors: Garvin J. L.
Published: December 2017

Glucose absorption was investigated in isolated perfused proximal straight tubules from rats by use of a newly developed ultramicrofluorometric assay. This assay takes advantage of the increase in fluorescence associated with the reduction of NAD to NADH while glucose is degraded to 6-phosphogluconate. When tubules were perfused at 6.70 +/- 0.42 nl.mm-1.min-1, the mean rate of glucose absorption was 11.0 +/- 1.0 pmol.mm-1.min-1, and the mean rate of fluid absorption was 0.61 +/- 0.06 nl.mm-1.min-1. Glucose transport is generally due to Na-glucose cotransport in the proximal nephron. In the rat proximal straight tubule, glucose absorption also appeared to be primarily due to Na-glucose cotransport, since 10(-4) M phlorizin inhibited absorption by 100%, as did inhibition of Na(+)-K(+)-ATPase by K removal. To determine the maximum rate of transport, tubules were perfused at rates greater than 20 nl.mm-1.min-1 with a solution containing 5.5 mM glucose. The maximum rate of glucose absorption was approximately 20 pmol.mm-1.min-1 under these conditions. The concentration of glucose that supports 50% of the maximum rate of absorption, Km, was 0.6 mM. When tubules were perfused at flow rates of less than or equal to 2 nl.mm-1.min-1, the luminal glucose concentration reached a limiting value of 0.47 mM with 5.5 mM glucose in the bath. The glucose permeability was 3.1 X 10(-6) cm/s.
Characterization of atrial natriuretic factor receptors in human glomerular epithelial and mesangial cells
Authors: Chansel D. , Pham P. , Nivez M. P. , Ardaillou R.
Published: December 2017

To evaluate the distribution and functions of receptors of atrial natriuretic factor (ANF) in human glomeruli, we studied the binding sites of ANF-(1-28) in homogeneous populations of human glomerular epithelial cells or mesangial cells. 125I-labeled ANF bound specifically to both cell types. Equilibrium saturation binding curves suggested one group of receptor sites in mesangial cells (Kd = 99 +/- 32 pmol/l, Bmax = 15.3 +/- 3.5 fmol/mg) but multiple groups in glomerular epithelial cells. Binding was greater at 37 than at 4 degrees C in mesangial cells. The reverse was observed in glomerular epithelial cells due to marked degradation of the tracer at 37 degrees C. The fractions of undisplaceable tracer in a hypertonic acid medium after 60 min incubation were 45 and 16% at 37 degrees C for glomerular epithelial and mesangial cells, respectively. ANF-(1–28) and C-ANF-(4–23), a specific ligand of clearance receptors, similarly inhibited 125I-ANF binding to mesangial cells, whereas [Ala7-Ala23]-ANF, a linear analogue, was slightly less potent. In epithelial cells, C-ANF-(4–23) competitively inhibited 125I-ANF binding but with a lower potency than ANF, whereas linear ANF at low concentrations (10–100 pmol/l) stimulated 125I-ANF binding. In addition, linear ANF markedly inhibited the degradation of 125I-ANF in the incubation medium of epithelial and mesangial cells, whereas thiorphan, an inhibitor of enkephalinase, was inactive. ANF-(1–28) stimulated cGMP production in glomerular epithelial cells but not in mesangial cells. Both analogues were inactive in both cell types and did not modify ANF-(1–28)-dependent cGMP synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)
Depressed distal tubule acidification corrects chloride-deplete alkalosis in rats
Authors: Wesson D. E.
Published: December 2017

We investigated the relative contributions made by the proximal and distal tubule to the correction of Cl-deplete metabolic alkalosis induced by systemic administration of NaCl. Free-flow micropuncture was used to examine net bicarbonate reabsorption in superficial proximal and distal tubules of anesthetized Munich-Wistar rats during maintenance and correction of chronic furosemide-induced Cl-deplete metabolic alkalosis. The distal tubule of animals with correcting vs. maintained alkalosis had a lower fractional reabsorption of bicarbonate (38 vs. 75%, P less than 0.001) and a lower slope of the linear regression comparing absorption to delivered load (0.48 vs. 0.99, P less than 0.02). By contrast, proximal tubule of animals with correcting vs. maintained alkalosis had fractional reabsorption (85 vs. 90%, P = 0.07) and slopes of the regression comparing reabsorption to filtered load (1.09 vs. 0.98, P = 0.48) that were not different. The data indicate that correction of Cl-deplete metabolic alkalosis induced by NaCl administration involves a qualitative decreased in bicarbonate reabsorption in distal tubule with maintenance of the same load-dependent relationship for bicarbonate reabsorption in proximal tubule.
Single-nephron responses to systemic administration of amino acids in dogs
Authors: Brown S. A. , Navar L. G.
Published: December 2017

It has been suggested that the tubuloglomerular feedback (TGF) system is responsible for renal vasodilation during systemic infusion of amino acid solutions. We evaluated the effect of intravenous administration of amino acids (serine, alanine, proline, and glycine; total dose of 0.075 mmol of amino acids.kg body wt-1.min-1) on whole kidney and single-nephron hemodynamics in pentobarbital sodium-anesthetized dogs. At spontaneous renal arterial pressure (RAP; 125.4 +/- 4.7 mmHg), measurements of single-nephron function obtained during tubular blockade, stop-flow pressure (SFP; 48.2 +/- 2.0 vs. 58.9 +/- 2.3 mmHg, P less than 0.01), and proximally determined single-nephron glomerular filtration rate (SNGFR-TPC; 73.9 +/- 7.0 vs. 93.4 +/- 7.6 nl/min, P less than 0.01) increased in parallel to the increases of outer cortical blood flow (OCBF; 15.4 +/- 1.1 vs. 19.1 +/- 1.5 units, P less than 0.05), renal blood flow (RBF; 4.60 +/- 0.18 vs. 5.73 +/- 0.22 ml.min-1.g kidney wt-1, P less than 0.01), and glomerular filtration rate (GFR; 0.885 +/- 0.034 vs. 1.116 +/- 0.034 ml.min-1.g kidney wt-1, P less than 0.01). Free-flow tubular fluid-to-plasma inulin ratios, determined from late proximal recollections during saline (control) and amino acid infusions failed to provide evidence for altered proximal reabsorption rate (1.63 +/- 0.12 vs. 1.58 +/- 0.17 during amino acids, NS). At reduced RAP (92.6 +/- 1.9 mmHg), where it is presumed that TGF-mediated vasodilation is already near maximal, the vasodilatory response to amino acid infusion was intact and single-nephron parameters measured during tubular blockade increased to the same extent as OCBF, RBF, and GFR.(ABSTRACT TRUNCATED AT 250 WORDS)
Polarity of kallikrein release and activation in perfused rat kidneys
Authors: Boric M. P. , Corthorn J. , Silva R. , Roblero J. S.
Published: December 2017

The polarity of release and activation of renal kallikrein and its regulation by adrenal hormones was studied in isolated perfused rat kidneys. Bilateral adrenalectomy (AX) produced a decrease in kallikrein and prokallikrein excretion into urine and perfusate of isolated kidneys, as well as in active kallikrein excretion in vivo. One-week treatment with deoxycorticosterone acetate (DOCA 2.5 mg/day) or dexamethasone (DEX 0.25 mg/day) increased the urinary output of active and total kallikrein above AX levels but below control. In contrast, neither corticoid increased enzyme secretion to perfusate. Regardless of AX or corticosteroid treatment, the prokallikrein fraction was 90% of total enzyme in perfusate and only 40% in urine. These results confirm that adrenal steroids are necessary for renal kallikrein synthesis and excretion; however, neither DOCA nor DEX appears to be a unique regulator for release or activation of this enzyme. In addition, whereas the processes of secretion and activation toward the urine are regulated in parallel, kallikrein release to the venous effluent seems to be regulated separately.
Dihydropyridine-sensitive cell volume regulation in proximal tubule: the calcium window
Authors: McCarty N. A. , O'Neil R. G.
Published: December 2017

The mechanism underlying the activation of hypotonic cell volume regulation was studied in rabbit proximal straight tubule (PST). When isolated non-perfused tubules were exposed to hypotonic solution, cells swelled rapidly and then underwent a regulatory volume decrease (RVD). The extent of regulation after swelling was highly dependent on extracellular Ca concentration ([Ca2+]o), with a half-maximal inhibition (K1/2) for [Ca2+]o of approximately 100 microM. RVD was blocked by the Ca-channel blockers verapamil, lanthanum, and the dihydropyridines (DHP) nifedipine and nitrendipine, implicating voltage-activated Ca channels in the RVD response. Using the fura-2 fluorescence-ratio technique, we observed that cell swelling caused a sustained rise in intracellular Ca ([Ca2+]i) only when [Ca2+]o was normal (1 mM) but not when [Ca2+]o was low (1-10 microM). Furthermore, external Ca was required early on during swelling to induce RVD. If RVD was initially blocked by reducing [Ca2+]o or by addition of verapamil during hypotonic swelling, volume regulation could only be restored by subsequently inducing Ca entry within the first 1 min or less of exposure to hypotonic solution. These data indicate a "calcium window" of less than 1 min, during which RVD is sensitive to Ca, and that part of the Ca-dependent mechanism responsible for achieving RVD undergoes inactivation after swelling. It is concluded that RVD in rabbit PST is modulated by Ca via a DHP-sensitive mechanism in a time-dependent manner.
Alpha 2-adrenergic receptors regulate Na(+)-H+ exchange via a cAMP-dependent mechanism
Authors: Clarke J. D. , Cragoe E. J. , Limbird L. E.
Published: December 2017

The mechanism by which alpha 2-adrenergic receptors regulate Na(+)-H+ exchange activity in opossum kidney (OK) cells was studied. Because receptors linked to inhibition of adenylate cyclase, like alpha 2-receptors, also can interact with additional signaling mechanisms, we examined specifically the role of adenosine 3',5'-cyclic monophosphate (cAMP) in the signaling pathway controlling Na(+)-H+ activity in OK cells. Parathyroid hormone (PTH), prostaglandin (PGE1), and forskolin, agents that stimulate cAMP production in these cells, inhibited the rate of amiloride-sensitive 22Na+ uptake by up to 40%. Epinephrine and UK 14304, acting through alpha 2-receptors, were able to reverse this inhibition of 22Na+ uptake to near-control levels and also attenuate PTH-, PGE1-, and forskolin-stimulated cAMP accumulation. Likewise, serotonin (5-HT) and SDZ21-009, acting through 5-HT1b receptors, could reverse inhibition of 22Na+ uptake and also attenuate stimulated cAMP accumulation. Neither epinephrine nor serotonin affected the rate of uninhibited 22Na+ uptake. Pertussis toxin pretreatment abolished the effects of alpha 2- and 5-HT1b receptors on both cAMP accumulation and 22Na+ uptake, suggesting that receptor-mediated inhibition of cAMP accumulation is involved in receptor modulation of Na(+)-H+ exchange activity. In contrast, epinephrine was not able to alter the inhibition of 22Na+ uptake mediated by the membrane-permeant cAMP analogues 8-bromo-cAMP and dibutyryl cAMP at any concentration of analogue that significantly inhibited 22Na+ uptake.(ABSTRACT TRUNCATED AT 250 WORDS)
Hyposmotic activation of Ca-activated K channels in cultured rabbit kidney proximal tubule cells
Authors: Kawahara K. , Ogawa A. , Suzuki M.
Published: December 2017

The effects of hypotonicity on K currents were examined in the single cells isolated from cultured rabbit kidney proximal tubule cells. Using the whole cell clamp technique [pipette-filling solution was 145 mM KCl with 0 Ca plus 0.08 mM ethylene glycol-bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid], we found that the K currents increased from 0.8 to 43.5 +/- 12.5 pA at a holding potential (Vp) = 0 mV in response to reduction of extracellular osmolality from 290 to 218 mosmol/kgH2O (n = 8). Removal of Ca from bath reduced osmotic activation of K currents by 74% (n = 10). Application of 5 mM Ba to the bath completely inhibited the K currents at Vp = 0 mV but not at Vp = 60 mV. Dominant K currents were shown to be Ca-activated (maxi) K channels by their single-channel conductance (175 +/- 8.6 pS) and Ca dependence. Relative permeability ratio (PK/PNa) was 9. In conclusion, hypotonic-induced cell swelling stimulates Ca-activated K channels, which may play a role in cell volume regulation.
Renal Na-myo-inositol cotransporter mRNA expression in Xenopus oocytes: regulation by hypertonicity
Authors: Kwon H. M. , Yamauchi A. , Uchida S. , Robey R. B. , Garcia-Perez A. , Burg M. B. , Handler J. S.
Published: December 2017

Canine renal cells in culture (MDCK cells) accumulate organic osmolytes, including myo-inositol (MI), in response to hypertonic stress. When medium tonicity is increased, intracellular concentration of MI rises because hypertonicity elicits increased uptake of MI via Na-MI cotransporter(s). To study the mechanism for this increase in cotransporter activity, poly(A)+ RNA isolated from MDCK cells maintained in hypertonic or isotonic medium was injected into Xenopus oocytes, and Na-dependent MI uptake was measured 3–5 days later. Poly(A)+ RNA from hypertonic cells induced clear expression of the cotransporter. In contrast, oocytes injected with poly(A)+ RNA isolated from MDCK cells maintained in isotonic medium exhibited cotransporter activity like oocytes injected with water. Upon size fractionation of RNA, peak activity appeared in a fraction that contained poly(A)+ RNA with median size of approximately 4 kilobases. Na-dependent MI uptake by poly(A)+ RNA-injected oocytes was inhibited by both phlorizin and phloretin. We suggest that hypertonicity-induced upregulation of the Na-MI cotransporter involves an increase in mRNA and synthesis of cotransporter protein(s).
Lymphatic drainage of the peritoneal cavity in sheep
Authors: Abernethy N. J. , Chin W. , Hay J. B. , Rodela H. , Oreopoulos D. , Johnston M. G.
Published: December 2017

Lymphatic drainage of the peritoneal cavity has been investigated in anesthetized sheep. Studies involving intraperitoneal administration of a complex of Evans blue dye and bovine serum albumin demonstrated the existence of three anatomically distinct pathways. In the first pathway, dye is removed from the peritoneal cavity by diaphragmatic lymphatics that pass into caudal sternal lymph nodes. Efferent lymphatics from these nodes transport the material to cranial sternal lymph nodes. Efferent cranial sternal lymphatics then convey the material either directly or indirectly, via tracheal lymphatic trunks, to the right lymph duct. In the second pathway, the complex is transported from the peritoneal cavity by diaphragmatic lymphatics that pass into the caudal mediastinal lymph node. Efferent lymphatic ducts from this node transport the material to the thoracic duct. The third pathway appears to involve transport of the dye across the mesothelial lining of the abdominal viscera and removal from the interstitium by afferent visceral lymphatics. Material taken up in this manner is ultimately transported to the thoracic duct by efferent visceral lymphatics. Experiments involving measurements of lymphatic absorption of 125I-labeled human serum albumin from the peritoneal cavity indicated that, over the 6-h period studied, 4.55 +/- 1.20 and 1.43 +/- 0.56% of the injected tracer could be recovered in thoracic duct lymph and caudal mediastinal efferent lymph, respectively, and the sum of these values represented 26% of the recovered radioactivity. On the other hand, 16.95 +/- 6.93% of the injected radioactivity could be found in the blood over the same period.(ABSTRACT TRUNCATED AT 250 WORDS)
Renal effects of prostaglandin inhibition during increases in renal venous pressure
Authors: Fiksen-Olsen M. J. , Romero J. C.
Published: December 2017

The role of prostaglandins (PGs) in mediating the hemodynamic and natriuretic responses to increases in renal interstitial pressure (RIP) induced by altering renal venous pressure (RVP) from control (3.6 +/- 0.6) to 15 and 30 mmHg was examined before and after PG inhibition in pentobarbital sodium-anesthetized dogs. These elevations of RVP resulted in RIP increasing from control (6 +/- 1) to 11 +/- 1 and 23 +/- 2 mmHg, respectively, without altering mean arterial pressure (MAP), renal blood flow (RBF), and glomerular filtration rate (GFR). Sodium excretion increased only when RVP reached 30 mmHg. During the inhibition of PG synthesis, 15 mmHg RVP induced a 10% decrease in RBF, and 30 mmHg RVP induced a further 20% decrease in RBF and a 50% decrease in GFR. PG synthesis inhibition did not alter either the RIP or the sodium excretory response. In conclusion, the natriuresis associated with the RIP increases induced by increasing RVP appears to be independent of PG synthesis. PGs, however, appear to be important for the maintenance of RBF and GFR during increased RVP. These findings suggest that different mechanisms are involved in the hemodynamic and natriuretic responses to arterial vs. venous pressure changes.
ANF-mediated renal cGMP generation in congestive heart failure
Authors: Margulies K. B. , Heublein D. M. , Perrella M. A. , Burnett J. C.
Published: December 2017

Previous studies have demonstrated that the biological actions of atrial natriuretic factor (ANF) are mediated via increases in its intracellular second messenger guanosine 3',5'-cyclic monophosphate (cGMP). Because cGMP egresses rapidly from target cells after ANF binding to particulate guanylate cyclase-linked receptors, extracellular cGMP may be a useful biological marker for the action of ANF in vivo under pathophysiological conditions. The present studies tested the hypothesis that the avid sodium retention and renal ANF resistance characteristic of chronic congestive heart failure (CHF) are associated with attenuated renal cGMP responses to ANF. We assessed the natriuretic and cGMP responses to endogenous and exogenous ANF during the evolution of CHF produced by 6 days of rapid ventricular pacing in conscious dogs (n = 6). Simultaneous measurement of plasma and urinary cGMP concentrations allowed determination of the net renal generation of cGMP, an indicator of the renal contribution to total urinary cGMP excretion. In early CHF, increased sodium excretion and renal cGMP production were observed in association with increases in plasma ANF. Exogenous ANF administration (10 micrograms/kg iv) before CHF also produced parallel increases in sodium excretion and renal cGMP production. In more advanced CHF produced by 6 days of pacing, we observed avid sodium retention in association with reversal of earlier increases in renal cGMP production despite progressive increases in circulating ANF. Natriuretic and renal cGMP responses to exogenous ANF were similarly attenuated in chronic CHF. These studies suggest that 1) renal cGMP production is a useful biological marker for the renal natriuretic action of ANF; 2) endogenous ANF contributes to the maintenance of sodium excretion in early CHF via increases in renal cGMP production; and 3) the avid sodium retention and renal ANF resistance in advanced CHF are, in part, linked to attenuated renal cGMP responses to endogenous and exogenous ANF.
Detection of the Na(+)-K(+)-ATPase alpha 3-isoform in multinucleated macrophages
Authors: Vignery A. , Wang F. , Qian H. Y. , Benz E. J. , Gilmore-Hebert M.
Published: December 2017

We previously reported that multinucleated macrophages express a high concentration of Na(+)-K(+)-ATPases that are concentrated on the nonadherent domain of their plasma membrane (A. Vignery, T. Niven-Fairchild, D. H. Ingbar, and M. Caplan. J. Histochem. Cytochem. 37: 1265-1271, 1989). We also showed that an increase in newly synthesized alpha-subunit occurred during cell culture and multinucleation. We now present evidence that macrophage multinucleation in vitro is accompanied by an increased accumulation of Na(+)-K(+)-ATPase alpha-subunit mRNA. Most interesting is the detection of significant amount of both alpha 1- and alpha 3-isoform mRNA and peptide in these cells by in situ hybridization, Northern and Western blot analyses. These qualitative and quantitative variations in Na(+)-K(+)-ATPase expression suggest that macrophage multinucleation is accompanied by a coordinated regulation of gene expression and that multinucleation confers a specific function to macrophages. Multinucleated macrophages offer a novel model system to investigate not only the specific function(s) of the alpha 3-isoform but also the role of the Na(+)-K(+)-ATPase in giant cells and osteoclasts.
Syncytial organization of cultured rat mesangial cells
Authors: Iijima K. , Moore L. C. , Goligorsky M. S.
Published: December 2017

To investigate communication competence of cultured rat mesangial cells, Lucifer yellow transfer was studied using microinjection and scrape-loading techniques. Both methods yielded results indicating considerable gap junctional communication between cultured mesangial cells. Gap junctional communication between mesangial cells was upregulated by adenosine 3',5'-cyclic monophosphate (cAMP). Conversely, cell-to-cell communication was attenuated by exposure to the tumor promoter phorbol myristate acetate, the Ca ionophore ionomycin, reduced oxygen intermediates, and cell acidification. Expression of voltage gated calcium channels by mesangial cells was studied microspectrofluorimetrically using fura-2 fluorescence. KCl-induced depolarization, BAY-K 8644, and readdition of calcium to Ca-free depolarizing medium all produced a nifedipine-inhibitable increase in cytosolic calcium concentration. The existence of voltage-gated calcium channels in communication-competent cells suggests the possibility of propagation of depolarizing signals across the syncytium. This was studied by microapplication of KCl to the microenvironment of a single cell and monitoring fura-2 fluorescence in remote cells. This maneuver resulted in propagating calcium waves in communication-competent monolayers; calcium waves could not be evoked in monolayers exposed to an alkanol-type gap junction uncoupler, octanol. It is concluded that cultured rat mesangial cells form a syncytium capable of propagating calcium transients from a single depolarized cell to its coupled neighbors.
Mechanisms of sodium retention in heart failure: relation to the renin-angiotensin-aldosterone system
Authors: Eiskjaer H. , Bagger J. P. , Danielsen H. , Jensen J. D. , Jespersen B. , Thomsen K. , Sorensen S. S. , Pedersen E. B.
Published: December 2017

Renal plasma flow (RPF), glomerular filtration rate (GFR), renal proximal tubular delivery of sodium and water evaluated by lithium clearance, and hormonal parameters were measured in 12 patients with congestive heart failure NYHA class II-IV before and after captopril treatment for 4 wk and in 13 healthy control subjects. RPF and GFR were significantly decreased in heart failure, whereas the filtration fraction (FF) was increased. Treatment with captopril increased RPF and decreased FF, whereas GFR was unchanged. Total and fractional urinary excretion of sodium were reduced in the patients compared with the controls, but increased after captopril. Fractional excretion of lithium was normal in heart failure and was increased by captopril. Atrial natriuretic peptide, guanosine 3',5'-cyclic monophosphate, and aldosterone in plasma were significantly elevated in heart failure and were reduced by treatment with captopril. Plasma renin activity was increased in patients, correlated inversely with RPF, and increased further after captopril treatment. It is concluded that the reduced sodium excretion in heart failure was caused by a combination of diminished glomerular filtration and enhanced tubular reabsorption beyond the proximal tubule and that treatment with captopril increased urinary sodium excretion partly due to an attenuated sodium reabsorption in the proximal tubule. The present data in patients with congestive heart failure are consistent with an increased intrarenal angiotensin II generation and an elevated plasma level of aldosterone being involved in the pathogenesis of the glomerular hemodynamic changes and the enhanced distal tubular reabsorption, respectively.