bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport and hydrolysis of glucagon in the proximal nephron
Authors: Peterson D. R. , Green E. A. , Oparil S. , Hjelle J. T.
Published: December 2017

Transport and hydrolysis of glucagon in the rabbit proximal nephron were studied. Iodinated glucagon (0.34 +/- 0.02 pg/nl, mean +/- SE) was microperfused (16.0 +/- 1.1 nl/min) in vitro through proximal straight nephron segments for 30 min. Radiolabeled material, primarily 125I-tyrosine, appeared in the bathing medium in a linear fashion as a function of time (0.406 pg glucagon X mm tubule length-1 X min-1). Hydrolysis of glucagon by proximal tubule homogenates was pH dependent, with a large peak of activity observed at pH 7.0-7.4 and a smaller one at pH 3.0. Analytical cell fractionation studies of proximal tubule cells revealed glucagon-hydrolyzing activity associated with the brush border and cytosol at pH 7.4. Less than 3% of activity was found associated with the contraluminal membrane. Substantial catabolism was observed at lysosomes on lowering the pH to 5.0. Incubation of glucagon directly in the presence of isolated renal cortical microvilli confirmed the presence of a high-capacity glucagon-degrading hydrolase. In addition to glucagon-hydrolyzing activity associated with the proximal nephron, noncortical activity was observed that was not accounted for by proximal tubule hydrolases. The data suggest several mechanisms for renal extraction of glucagon, including hydrolysis by enzymes at the brush border of the proximal tubule, prior to reabsorption of metabolites there. Conversely, enzymes associated with the contraluminal membrane of the proximal nephron probably contribute little to its hydrolysis. Nonproximal extracortical degradation of glucagon may account for its previously observed peritubular hydrolysis.
Renal effects of ANP without changes in glomerular filtration rate and blood pressure
Authors: Salazar F. J. , Fiksen-Olsen M. J. , Opgenorth T. J. , Granger J. P. , Burnett J. C. , Romero J. C.
Published: December 2017

The aim of the present study was to determine if atrial natriuretic peptide (ANP)-induced natriuresis is dependent on increases in glomerular filtration rate (GFR). Intrarenal blood flow distribution and urinary excretion of prostaglandins were also determined during the infusion of a dose of ANP that does not induce changes in GFR and mean arterial pressure (MAP). It was found that the intrarenal infusion of ANP (8-33) at a dose of 0.05 micrograms X kg-1. min-1 in seven anesthetized dogs did not produce any change in GFR or MAP, but its natriuretic effect was similar to that obtained by a larger dose (0.3 micrograms X kg-1 X min-1, n = 5) that produces significant changes in both MAP and GFR. The natriuresis induced by the lower dose of ANP was associated with a redistribution (P less than 0.05) of renal blood flow (RBF) from the superficial to the juxtamedullary cortex and with an increase (P less than 0.05) in urinary excretion of prostaglandins E2 (PGE2) (0.8 +/- 0.2 to 2.4 +/- 1.0 ng/min) and 6-keto-F1 alpha (6-keto-PGF1 alpha) (2.8 +/- 0.6 to 5.5 +/- 1.7 ng/min). Renin secretion rate decreased from 610 +/- 165 to 279 +/- 61 ng angiotensin I/min. These results show that the natriuresis induced by ANP is not necessarily produced by an increase in GFR and is associated with a redistribution of RBF to the deep cortex and an increase in urinary excretion of PGE2 and 6-keto-PGF1 alpha.
Sodium chloride, extracellular fluid volume, and blood pressure regulation
Authors: Hamlyn J. M. , Blaustein M. P.
Published: December 2017

Data from humans and experimental animals indicate that hypertensive diseases triggered by extracellular fluid volume expansion are characterized, in their chronic phases, by relatively normal blood volume (BV) and heightened pressure-volume relationship may be viewed as corresponding to a condition of "virtual hypervolemia," where BV is inappropriately "high" relative to blood pressure. The limited data available on the phasic relationship between these variables indicate that the BV expansion appears to be a prerequisite to alterations in vascular ion metabolism, that both of these changes precede the rise in blood pressure, and that structures within the central nervous system may be a critical link between the body fluid volumes and vascular functional changes. In contrast, hypertensive diseases triggered by secretion of pressor agents or their precursors appear to be characterized in their chronic phases by low BV. These relationships and the associated alterations in plasma aldosterone and renin levels are summarized for a variety of clinical syndromes, including essential hypertension and pregnancy-induced hypertension. Direct or indirect evidence of a primary or secondary defect in renal function is apparent as an underlying event in many of these diseases.
Distinct localization of atrial natriuretic factor and angiotensin II binding sites in the glomerulus
Authors: Bianchi C. , Gutkowska J. , Thibault G. , Garcia R. , Genest J. , Cantin M.
Published: December 2017

A comparative study of the localization of 125I-labeled atrial natriuretic factor (ANF) and 125I-labeled angiotensin II (ANG II) binding sites in the glomerulus of the rat, after an intravascular injection, has been done by ultrastructural radioautography. 125I-ANF binding sites are localized predominantly on the podocytes of the visceral epithelium (63%) followed by the endothelium of capillaries (14%), the parietal epithelium (13%), and finally mesangial cells (10%). In a comparative study, it was confirmed that 125I-ANG II uptake is localized predominantly on mesangial cells (60%) followed by epithelial visceral cells (23%) and the endothelium of capillaries (16%). Using isolated rat glomeruli, it was confirmed that ANG II decreases glomerular size (maximum effect of 15%) with an apparent half maximum effective concentration (EC50) between 10(-9) and 10(-8) M. Although ANF alone has no apparent effect on glomerular size, it inhibits the contractile effect of ANG II with a half maximum inhibitory concentration (IC50) between 10(-11) and 10(-10) M. These results suggest that an intraglomerular mechanism other than glomerular arteriolar resistance may be involved in the modulation of glomerular filtration rate by ANF. The presence of 125I-ANF uptake mainly in foot processes of visceral epithelial cells of glomeruli in vivo and the inhibition of ANG II decrease in glomerular size by ANF in vitro raise the possibility that ANF may regulate the ultrafiltration coefficient by two mechanisms: modulation of glomerular permeability, and surface area.
Effect of cAMP on prostaglandin E2 production in cultured rat inner medullary collecting tubule cells
Authors: Teitelbaum I. , Mansour J. N. , Berl T.
Published: December 2017

Studies were performed to determine whether cAMP impairs prostaglandin (PG) E2 production in a homogeneous population of cultured rat inner medullary collecting duct cells. Three structurally different cAMP analogues were shown to decrease PGE2 synthesis by 48.4% in the basal state and by 49.3% in response to the divalent cation ionophore A23187 (5 microM). Thromboxane B2 production was similarly suppressed. An increase in endogenous cAMP by forskolin also decreased PGE2 synthesis. To determine the locus of the cAMP effect we examined the response to exogenously added arachidonic acid. At a concentration of arachidonic acid (5 micrograms/ml) sufficient to render the phospholipase-dependent fraction negligible (as evidenced by the lack of a mepacrine effect), cAMP had no effect on PGE2 production, suggesting phospholipase as the site of cAMP action. Further evidence for a phospholipase-mediated mechanism derives from studies employing [5,6,8,9,11,12,14,15-3H(N)]arachidonic acid in which cAMP analogues had no effect on the rate of cellular arachidonic acid incorporation, but did impair the release of tritiated arachidonic acid in response to ionophore. These results suggest the existence of a negative feedback system that, by impairing phospholipase activity and PGE2 synthesis, could enhance the action of cAMP in the antidiuretic state.
Effects of mineralocorticoids on transport properties of cortical collecting duct basolateral membrane
Authors: Sansom S. C. , O'Neil R. G.
Published: December 2017

The effects of long-term mineralocorticoid (deoxycorticosterone acetate, DOCA) elevation for 9-16 days on the active and passive transport properties of the basolateral cell membrane of rabbit cortical collecting ducts were assessed using microelectrode techniques. It was found that both the transepithelial membrane voltage (Vte) and basolateral membrane voltage (Vb) hyperpolarized and the basolateral membrane conductance (Gb) increased on chronic elevation of mineralocorticoid levels. Barium (5 mM) addition to the bathing solution effectively blocked an induced K+ current across the basolateral cell membrane without an immediate affect on the other barriers. Therefore Ba2+ was used to quantitate the basolateral cell membrane K+ conductance (GbK). It was found that GbK increased from 1.0 +/- 0.2 mS X cm-2 (controls) to 3.7 +/- 1.0 mS X cm-2 in DOCA-treated animals. The basolateral membrane electrogenic pump current (Ibact) was quantitated from the change in the basolateral membrane equivalent emf on addition of either ouabain (0.1 mM) to the bath or of amiloride (50 microM) to the perfusate. There was a large increase in Ibact from 32 microA X cm-2 in controls to 195 microA X cm-2 in the DOCA-treated group. In addition, the estimated Na+-to-K+ coupling ratio of the Na+ pump was observed to increase from 1.6 to 1.0 in the control group to 3.2 to 1.0 in the DOCA-treated group. The estimated basolateral membrane passive K+ current (IbK) increased from a value that was not significantly different from 0 in controls to approximately -45 microA X cm-2 (from bath to cell) in the DOCA-treated group. These findings support a model whereby mineralocorticoids induce an increase in electrogenic Na+ pump activity in response to chronically elevated rates of Na+ transport. This results in a hyperpolarization of Vb, which is well above EbK, thereby resulting in a net driving force for K+ uptake into the cell, bringing about an increased rate of K+ secretion.
Effect of acute acidemia on phosphate uptake by renal proximal tubular brush-border membranes
Authors: Levine B. S. , Kraut J. A. , Mishler D. R. , Crooks P. W.
Published: December 2017

Prolonged metabolic acidosis is associated with depressed phosphate (Pi) uptake by the brush-border membrane (BBM) of the proximal tubule. To examine if changes in systemic pH underlie this inhibition, we measured Pi transport by renal cortical BBM from thyroparathyroidectomized rats with respiratory or metabolic acidosis of 1 or 3 h, respectively, and in appropriate controls. Also, Pi transport was measured in BBM prepared using tissue slices from nonacidotic rats that were preincubated for 20 or 45 min at either pH 6.9 (HCO3 = 10 mM, CO2 = 10%) or 7.4 (HCO3 = 10 mM, CO2 = 2.5%). Despite comparable acidemia (pH 7.06 +/- 0.05 with respiratory acidosis and 7.10 +/- 0.03 with metabolic acidosis), Na-dependent Pi uptake at 5 s incubation was reduced by 15.2 +/- 3.5% with respiratory acidosis compared with paired controls. It was not altered with metabolic acidosis. Vmax in respiratory acidosis (1.2 nmol X mg protein-1 X 5 s-1) was less than in controls (1.6); Kt was similar in both groups. 22Na transport and Na-dependent glucose transport were unchanged. Plasma phosphorus (P) increased from 8.75 +/- 0.35 mg/dl to 12.42 +/- 1.9 with respiratory acidosis. Therefore BBM vesicles transport was measured in controls after plasma P was raised. Under these conditions, Pi transport was similar to that with respiratory acidosis. Also Pi transport by BBM was unchanged when tissue slices were preincubated in vitro at high CO2 concentrations for 20 or 45 min. Thus respiratory acidosis specifically inhibits Na-dependent Pi transport by decreasing the number or rate of the BBM Pi carrier.(ABSTRACT TRUNCATED AT 250 WORDS)
A new microelectrode method for simultaneous measurement of pH and PCO2
Authors: Bomsztyk K. , Calalb M. B.
Published: December 2017

A liquid-membrane pH-PCO2 microelectrode is described for the simultaneous measurement of pH and PCO2 in tissues and body fluids. The microelectrode is simple and easy to fabricate. It can be used to measure HCO3 concentration in solutions at chemical equilibrium. In the physiological range the microelectrode response is linear with nearly Nernstian slopes for PCO2 (61.2 +/- 2.0 mV/log10 PCO2) and pH (63.7 +/- 1.9 mV/pH units) (n = 14) at 37 degrees C. The PCO2 response is independent of the solutions' pH, anionic composition, and presence of serum proteins. In randomly micropunctured rat surface proximal tubules, pH averaged 6.80 +/- 0.04 and PCO2 averaged 57.7 +/- 4.6 mmHg (n = 22), whereas in the adjacent peritubular capillaries pH was higher (7.27 +/- 0.03) but PCO2 was not different (55.7 +/- 4.6 mmHg) (n = 22). Systemic arterial PCO2 was significantly lower compared with the renal cortex and averaged 37.4 +/- 2.4 mmHg (n = 14). Directly measured and pH-PCO2 microelectrode-derived HCO3 concentrations in systemic arterial blood, surface fluid bathing the kidney, and randomly micropunctured proximal tubules were approximately equal.
Renal effects of angiotensin II: modulation by calcium and cyclooxygenase products
Authors: Kasiske B. L. , O'Donnell M. P. , Keane W. F.
Published: December 2017

Modulation of angiotensin II effects on renal function by extracellular calcium levels and cyclooxygenase products was evaluated using the isolated perfused rat kidney. Kidneys from normal male Sprague-Dawley rats were perfused at constant pressure. After base-line assessment of function, angiotensin II was administered as a bolus and constant infusion; group 1 with normal ionized calcium and 1.2 ng/min angiotensin II, group 2 with normal ionized calcium and 0.6 ng/min angiotensin II, group 3 with low ionized calcium and 1.2 ng/min angiotensin II, and group 4 with indomethacin, low ionized calcium, and 1.2 ng/min angiotensin II. Angiotensin II caused a marked fall in inulin clearance (CIn) in groups 1 and 2. With low ionized calcium (group 3), angiotensin II increased resistance to the same degree as in group 2, but in contrast to group 2, CIn was unchanged. Kidneys perfused with indomethacin (group 4) had marked angiotensin II-induced declines in CIn that rapidly returned to base line despite persistently elevated resistance. Thus the results demonstrated that both calcium and cyclooxygenase products may directly modulate the effects of angiotensin II on renal function. These effects involve more than modulation of angiotensin II-induced vasoconstriction.
Renal effects of atrial natriuretic factor in primate
Authors: Bourgoignie J. J. , Gavellas G. , Hwang K. H.
Published: December 2017

Baboons (Papio hamadryas) were infused intravenously with a nonhypotensive dose (0.1 microgram X min-1 X kg-1) of synthetic human atriopeptin III (ANF) for 60 min. Throughout the infusion in intact animals, ANF significantly increased glomerular filtration rate (GFR) (clearance of inulin) (P less than 0.001), and, to a lesser extent, total renal plasma flow (RPF) [clearance of p-aminohippurate (PAH)] (P less than 0.02) and filtration fraction (P less than 0.02). Concomitant increases in urinary flow rate and in the excretion of osmoles, sodium, chloride, potassium, phosphorus, and calcium were highly significant (less than 0.001 for all). To minimize the hemodynamic impact of ANF on GFR, the same dose of ANF was infused into the same animals 8 wk after uninephrectomy. Base-line single-kidney GFR was then 50% increased. With ANF infusion RPF increased significantly (P less than 0.02), as in intact baboons, but ANF then had only marginally significant effects on GFR (P = 0.06) and insignificant effects on filtration fraction (P = 0.17). Nevertheless, the changes in urinary flow rate and solute excretion rates were highly significant (P less than 0.001 to less than 0.007). In both groups, all changes developed rapidly, were sustained during the infusion of ANF, and were readily reversible within 15 to 30 min of cessation of ANF infusion. The data dissociate in uninephrectomized primate the effects of ANF on water and solute excretion from those on GFR and filtration fraction. Both in intact and in uninephrectomized baboons, the changes in water and solute excretion were associated with small but significant changes in RPF.
Involvement of calmodulin in mediating inhibitory action of intracellular Ca2+ on renin secretion
Authors: Park C. S. , Honeyman T. W. , Chung E. S. , Lee J. S. , Sigmon D. H. , Fray J. C.
Published: December 2017

This study sought to elucidate further the cellular mechanism(s) involved in the control of renin secretion by Ca2+. The rate of renin secretion in vitro by rabbit and dog renal cortical slices was inversely related to medium Ca2+ concentration. The inverse relationship was observed only when the cell membrane permeability to Ca2+ was increased by K+ depolarization, suggesting that the Ca2+ concentration in the juxtaglomerular cell modulates renin secretion. From this relationship, renin secretion appears to turn on at intracellular Ca2+ concentrations between 10(-8) and 10(-7) M. Calmidazolium, a potent calmodulin antagonist, markedly stimulated basal renin secretion in a concentration-dependent manner. Pretreatment of slices with calmidazolium blocked the inhibition of renin secretion by high-K+ medium. Calmidazolium and several other calmodulin antagonists (W-7, W-13, and trifluoperazine) partly or fully reversed the inhibition of renin secretion previously inhibited by high-K+ medium in the order of their potencies as calmodulin antagonists. Indeed, W-5, a biologically inactive structural analogue of W-7, was without effect. These results support the hypothesis that renin secretion is inversely related to intracellular Ca2+ and that Ca2+ inhibits renin secretion by a calmodulin-dependent process.
Electrophysiological heterogeneity of proximal convoluted tubules in Amphiuma kidney
Authors: Lang F. , Oberleithner H. , Giebisch G.
Published: December 2017

The present study was designed to identify functional differences between dark (early to mid) and white (late) proximal tubule segments in Amphiuma kidney. The potential difference across the peritubular cell membrane (Vb), the luminal cell membrane (Va), and the epithelium (Vte) are not significantly different between dark and white segments. Cellular and luminal cable analysis reveals that the resistance of the cell membranes in parallel is lower in dark (28.6 +/- 3.2 k omega X cm) than in white segments (63.2 +/- 5.0 k omega X cm) in contrast to the transepithelial resistance, which is higher in dark (26.6 +/- 5.5 k omega X cm) than in white (3.5 +/- 0.7 k omega X cm) segments. A step-increase of peritubular potassium (from 2.5 +/- 12.5 mmol/liter) depolarizes Vb more in white (20.1 +/- 1.2 mV) than in dark (7.2 +/- 0.4 mV) segments, whereas addition of bicarbonate to peritubular perfusate hyperpolarizes Vb more in dark (-22.4 +/- 1.6 mV) than in white (-5.9 +/- 0.7 mV) segments. An increase of luminal potassium depolarizes Va more in dark (21.3 +/- 2.0 mV) than in white (9.3 +/- 1.9 mV) segments. Similarly luminal glucose depolarizes Va more in dark (10.7 +/- 1.2 mV) than in white segments (3.2 +/- 1.4 mV). Partial peritubular replacement of NaCl and reduction of peritubular chloride polarize Vte more in white (9.6 +/- 1.0 and 28.9 +/- 2.9 mV) than in dark segments (7.0 +/- 0.5 and 15.5 +/- 1.9 mV). In conclusion, compared with white segments, dark segments have lower cell membrane and higher shunt resistances, lower potassium and higher bicarbonate conductances of the peritubular cell membrane, and a higher capacity to reabsorb glucose. Paracellular shunt chloride conductance is relatively high in both segments.
Electrophysiological studies on primary cultures of proximal tubule cells
Authors: Bello-Reuss Elsa , Weber Mark R.
Published: December 2017

Page F490: Elsa Bello-Reuss and Mark R. Weber. Electrophysiological studies on primary cultures of proximal tubule cells. Page F491: The “proximal medium” composition given in the article is incorrect. The modified Eagle's medium contained 25 mM HEPES and 21.5 mM NaHCO3 as main buffers; 25 nM sodium selenite and 0.1 mM l-alanine, l-aspartic acid, l-asparagine, l-glutamic acid, glycine, l-proline, and l-serine. Concentrations of other additives and pH are correct in the article.
Activation of ion transport systems during cell volume regulation
Authors: Eveloff J. L. , Warnock D. G.
Published: December 2017

This review discusses the activation of transport pathways during volume regulation, including their characteristics, the possible biochemical pathways that may mediate the activation of transport pathways, and the relations between volume regulation and transepithelial transport in renal cells. Many cells regulate their volume when exposed to an anisotonic medium. The changes in cell volume are caused by activation of ion transport pathways, plus the accompanying osmotically driven water movement such that cell volume returns toward normal levels. The swelling of hypertonically shrunken cells is termed regulatory volume increase (RVI) and involves an influx of NaCl into the cell via either activation of Na-Cl, Na-K-2Cl cotransport systems, or Na+-H+ and Cl(-)-HCO3- exchangers. The reshrinking of hypotonically swollen cells is termed regulatory volume decrease (RVD) and involves an efflux of KCl and water from the cell by activation of either separate K+ and Cl-conductances, a K-Cl cotransport system, or parallel K+-H+ and Cl(-)-HCO3- exchangers. The biochemical mechanisms involved in the activation of transport systems are largely unknown, however, the phosphoinositide pathway may be implicated in RVI; phorbol esters, cGMP, and Ca2+ affect the process of volume regulation. Renal tubular cells, as well as the blood cells that traverse the medulla, are subjected to increasing osmotic gradients from the corticomedullary junction to the papillary tip, as well as changing interstitial and tubule fluid osmolarity, depending on the diuretic state of the animal. Medullary cells from the loop of Henle and the papilla can volume regulate by activating Na-K-2Cl cotransport or Na+-H+ and Cl(-)-HCO3- exchange systems. Both Na-Cl and Na-K-2Cl cotransport systems have been identified in the medullary Loop of Henle and it is postulated that the Na-K-2Cl cotransport system predominates during RVI and affects transepithelial NaCl transport while the Na-Cl cotransport system may function during RVD in these cells.
Glucose metabolism in muscle of sedentary and exercised rats with azotemia
Authors: Davis T. A. , Klahr S. , Karl I. E.
Published: December 2017

Insulin resistance has been demonstrated in chronic renal failure patients and may be improved by exercise training, but the mechanisms have not been identified. In this study, the response of glucose uptake, glycogen synthesis, and glucose utilization via glycolysis (glycolytic utilization) to stimulation by insulin and/or acute exercise were determined in isolated muscles from rats with moderate renal insufficiency that were exercise trained or remained sedentary. Moderate renal insufficiency had no effect on the basal rate, insulin sensitivity, or insulin responsiveness of glucose uptake, glycogen synthesis, or glycolytic utilization in muscle. The enhanced insulin responsiveness of both glycogen synthesis and glucose uptake following acute exercise, noted in control animals, was less in rats with moderate renal insufficiency, but the enhanced basal rate and insulin sensitivity after exercise were unaffected by moderate renal insufficiency. Exercise training increased the insulin sensitivity and responsiveness of muscle glucose uptake and glycolytic utilization in rats with moderate renal insufficiency and in controls. The effects of acute exercise and exercise training on insulin responsiveness of glucose uptake were additive in controls but not in animals with moderate renal insufficiency. These findings are compatible with the concept that moderate renal insufficiency is associated with a postreceptor defect in insulin's action in muscle, detectable only following maximal stimulation of glucose transport by insulin and exercise, and partially correctable by exercise training.
Electrochemical analysis of renal Na+-glucose cotransport in salamander proximal tubules
Authors: Morgunov N. , Boulpaep E. L.
Published: December 2017

The changes in electrical membrane parameters and intracellular sodium activity associated with the absorption of D-glucose were studied in the isolated perfused proximal tubule of the Ambystoma tigrinum kidney. The addition of 10 mM D-glucose to a substrate-free luminal perfusate depolarized the basolateral and luminal membrane potentials by -16.2 +/- 0.9 mV and +20.4 +/- 0.9 mV, respectively (P less than 0.01), increased intracellular sodium activity (acellNa) by 5.1 +/- 0.8 mM (P less than 0.01) and significantly (P less than 0.01) decreased luminal membrane resistance from 2,859 +/- 454 to 1,483 +/- 120 omega X cm2. Both the electrogenic response and the change in acellNa induced by luminal glucose were a saturating function of luminal glucose and sodium concentrations. The electrogenic response to luminal glucose was sensitive to intracellular glucose concentration and the change in acellNa induced by luminal glucose was sensitive to intracellular sodium concentrations. Within the physiological range of membrane potentials and studied, the sodium-glucose cotransporter is more sensitive to a decrease in a favorable electrical gradient than to an increase in a favourable chemical gradient for sodium across the luminal membrane.
Modification of tubuloglomerular feedback signal by dietary protein
Authors: Seney F. D. , Persson E. G. , Wright F. S.
Published: December 2017

Compared with the effects of a 6% protein diet, feeding rats a 40% protein diet for 10 days increases glomerular filtration rate and decreases the activity of the tubuloglomerular (TG) feedback control system. The decrease in TG feedback activity results from an increase in the threshold at which the loop of Henle flow rate initiates feedback responses. To determine whether this protein-dependent shift in the TG feedback response curve is caused by changes in either the signal or the sensing mechanism in the feedback pathway, we used micropuncture and microperfusion techniques to study the TG feedback system of rats fed high- or low-protein (40 or 6% casein) diets for approximately 7-10 days. Compared with the rats fed the low-protein diet, in the high-protein group distally measured single nephron glomerular filtration rate was 17% higher, and Na and Cl concentrations in early distal tubule fluid were 30-50% lower. Early distal osmolality was not different in the two groups. TG feedback responses assessed by changes in stop-flow pressure during perfusion of the distal nephron with NaCl solutions did not differ between diet groups. We conclude that the sensing mechanism in the TG feedback system is not altered by this manipulation of dietary protein, whereas the signal eliciting the TG feedback response is affected. Because rats fed a high-protein diet have higher rates of Na and Cl absorption between the late proximal and early distal tubules than do rats fed a low-protein diet, early distal Na and Cl concentrations are reduced, and the signal for TG feedback is diminished in rats fed the high-protein diet.
Effects of hypoproteinemia on renal hemodynamics, arterial pressure, and fluid volume
Authors: Manning R. D.
Published: December 2017

The effects of long-term hypoproteinemia on renal hemodynamics, arterial pressure, and fluid volume were studied in eight conscious dogs over a 34-day period. Plasma protein concentration (PPC) was decreased by daily plasmapheresis, and the effects of decreasing and increasing sodium intake were measured. By the 12th day of plasmapheresis, during which sodium intake was 30 meq/day, PPC had decreased to 2.5 g/dl from a control value of 7.2 g/dl, mean arterial pressure had decreased to 78% of control, glomerular filtration rate (GFR) was 75.2% of control, and urinary sodium excretion was decreased. By day 18 of plasmapheresis, estimated renal plasma flow (ERPF) was decreased to 60% of control due to the decreased arterial pressure and an increase in renal vascular resistance. Also, plasma renin activity and plasma aldosterone concentration were both increased, and the relationship between mean arterial pressure and urinary sodium excretion was distinctly shifted to the left along the arterial pressure axis. In contradistinction to acute experiments, chronic hypoproteinemia results in decreases in GFR, ERPF, and urinary sodium excretion and has marked effects on both fluid volume and arterial pressure regulation.
Regulation of urea synthesis by acid-base balance in vivo: role of NH3 concentration
Authors: Cheema-Dhadli S. , Jungas R. L. , Halperin M. L.
Published: December 2017

The purpose of this study was to clarify how changes in acid-base balance influence the rate of urea synthesis in vivo. Since ureagenesis was increased by an ammonium infusion into rats, regulation seemed to be a function of the blood ammonium concentration. The rate of urea synthesis was constant at a fixed rate of ammonium infusion and independent of the conjugate base infused, chloride or bicarbonate. The steady-state blood ammonium concentration was higher in the rats that developed metabolic acidosis. Thus it appeared that regulation was not directly mediated by this ammonium concentration per se. The rate of urea synthesis was also independent of the blood pH. Accordingly, the rate of urea synthesis was examined as a function of the plasma NH3 concentration. The rate of ureagenesis was found to be directly proportional to the plasma NH3 concentration. Assuming that plasma NH3 levels reflect those in mitochondria, the NH3 concentration yielding half-maximal rates of urea synthesis (close to 2 microM) was in the same range as Km for the rate-limiting step in ureagenesis, carbamoyl phosphate synthetase (EC 6.3.4.16). These results suggest that, at a constant ammonium concentration, the decreased rate of ureagenesis caused by a pH fall in vitro could reflect an acidosis-induced decline in the concentration of true substrate (NH3) for this pathway.
Evidence that parallel Na+-H+ and Cl(-)-HCO3-(OH-) antiporters transport NaCl in the proximal tubule
Authors: Baum M.
Published: December 2017

The present in vitro microperfusion study examined whether active NaCl transport in the proximal convoluted tubule (PCT) occurs via parallel Na+-H+ and Cl(-)-HCO3-(OH-) exchangers. PCT were perfused with a high-chloride, low-bicarbonate solution simulating late proximal tubular fluid, and were bathed in a similar solution containing 6 g/dl albumin. In this setting the driving forces responsible for passive NaCl transport are eliminated. Addition of 0.1 or 0.5 mM luminal 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), 0.5 mM luminal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), or 0.1 mM bath ethoxyzolamide, a lipophilic carbonic anhydrase inhibitor, resulted in an approximately 50% reduction in volume absorption. Inhibition of the Na+-H+ antiporter with 1.0 mM luminal amiloride inhibited volume absorption by 50%. The transepithelial potential difference (PD) was not significantly different from zero, consistent with an electroneutral mechanism for active NaCl transport. The effect of a Cl(-)-HCO3-(OH-) exchanger on acidification was examined in PCT perfused with an ultrafiltrate-like solution and bathed in a serumlike albumin solution. Addition of 0.5 mM DIDS did not significantly decrease volume absorption, demonstrating that luminal DIDS did not result in a nonspecific decrease in solute transport. Luminal DIDS significantly stimulated bicarbonate absorption, consistent with a Na+-H+ antiporter running in parallel with a Cl(-)-HCO3-(OH-) antiporter, which exchanges luminal Cl- for cellular HCO3- (or OH-). In conclusion, these data are consistent with parallel Na+-H+ and Cl(-)-HCO3-(OH-) antiporters mediating neutral active NaCl transport in the PCT.
Profiles of water and solute transport along long-loop descending limb: analysis by mathematical model
Authors: Taniguchi J. , Tabei K. , Imai M.
Published: December 2017

We simulated profiles of water and solute transport along the descending limb of the long-loop nephron by a mathematical model based on mass balance equations for water, sodium, potassium, and urea, using phenomenological coefficients reported for hamsters. We assumed that interstitial concentration of sodium, potassium, and urea increased linearly along the descending limb from 150 to 350, from 5 to 50, and from 5 to 300 mM, respectively. Under this condition an increase in osmolality at the end-descending limb was mainly accounted for by the absorption of water. Considerable amounts of potassium and urea were secreted along the descending limb. Sodium was reabsorbed rather than secreted along the descending limb by both diffusion and solvent drag. The secreted amounts of urea and potassium were comparable to those observed by micropuncture studies. The sodium concentration in the lumen was higher than in the interstitium, with the transmural sodium gradient being 15 meq/liter at the hairpin turn. The potassium mass flow rate at the end-descending limb increased by 2.4 times. Large variations in potassium concentration of the delivered fluid scarcely changed the potassium mass flow rate at the end-descending limb. The secretion of urea and potassium and the reabsorption of sodium were increased as a function of delivered flow rate. An increase in corticomedullary urea gradient decreased the net potassium secretion along the descending limb. When the transport parameters for rabbits were used, both reabsorption of sodium and addition of urea were decreased, but a similar amount of potassium was secreted. These analyses indicate that the mathematical model that takes the species difference and internephron heterogeneity into consideration is useful in illustrating the transport processes along the descending limb of Henle's loop under various physiological and pathophysiological conditions.
Renal hemodynamic, fluid volume, and arterial pressure changes during hyperproteinemia
Authors: Manning R. D.
Published: December 2017

The chronic effects of hyperproteinemia on renal hemodynamics, fluid volume, and arterial pressure were determined in six conscious dogs over a 32-day period. Plasma protein concentration was increased by intravenous infusion of approximately 300 ml/day of previously collected autologous plasma, and the responses to changes in sodium intake were studied. By the end of a 9-day period of hyperproteinemia and normal sodium intake, plasma protein concentration had increased 2.2 g/dl, plasma colloid osmotic pressure had increased 7-8 mmHg, mean arterial pressure had increased 12 mmHg, glomerular filtration rate (GFR) had increased 15%, estimated renal plasma flow (ERPF) had increased 51% primarily due to renal vasodilatation, and filtration fraction had decreased 23%. Also, sodium balance was negative, water balance was positive, sodium iothalamate space had increased, plasma sodium concentration had decreased, and the relationship between mean arterial pressure and urinary sodium excretion was shifted to the right along the arterial pressure axis. In conclusion, long-term increases of plasma protein concentration result in a marked increase in ERPF as well as significant increases in GFR, extracellular fluid volume, and arterial pressure.
Corticosteroids decrease glomerular angiotensin receptors
Authors: Douglas J. G.
Published: December 2017

Angiotensin II (ANG II) receptors of glomerular mesangial cells are regulated in vivo by changes in Na balance, effects that are presumed to be secondary to changes in circulating ANG II. However, since changes in ANG II were accompanied by parallel changes in plasma aldosterone in all models tested, it is possible that aldosterone may have also participated in the modulation of glomerular ANG II receptors. To test this hypothesis, short-term aldosterone infusions within the physiological range were employed to favor actions that would be mediated through a high-affinity mineralocorticoid receptor. The glucocorticoid, dexamethasone, was also tested to determine the mineralocorticoid specificity of the response. Two infusion rates were associated with a decrease in glomerular ANG II receptor density of 33 and 45%, respectively. There were no changes in the affinity of ANG II in either tissue or in adrenal receptor density. Serum potassium and urinary Na/K ratio were lower in the aldosterone group. Spironolactone abolished the effect of aldosterone consistent with an action mediated through a specific mineralocorticoid receptor. Dexamethasone administration produced similar downregulation of glomerular ANG II receptor and was unaccompanied by a change in electrolyte balance or blood volume. These studies support the hypothesis that corticosteroids modulate glomerular ANG II receptors and validate the complexity of glomerular receptor modulation. The downregulation observed would be expected to diminish the ability of ANG II to influence glomerular hemodynamics in models such as mineralocorticoid and glucocorticoid-induced hypertension.
Effect of potassium depletion and protein intake in vivo on renal tubular bicarbonate transport in vitro
Authors: McKinney T. D. , Davidson K. K.
Published: December 2017

These studies evaluated the effect of decreased dietary potassium and increased dietary protein content in rabbits on systemic acid-base parameters, urine pH, and segmental renal tubular bicarbonate handling in vitro. Animals fed a potassium-deficient high-protein diet (KD) for 2 wk developed metabolic acidosis (arterial blood pH 7.31 vs. 7.43) and excreted a more acid urine than control animals fed a diet with normal amounts of potassium and protein; whereas, animals fed the same potassium deficient diet to which supplemental potassium was added (KD + K+) excreted an even more acid urine and had a blood pH of 7.36. In superficial proximal convoluted and straight tubules, there were no differences in rates of fluid and total CO2 absorption between control and KD tubules. Cortical collecting tubules obtained from KD and KD + K+ animals absorbed, and control tubules secreted total CO2 in vitro. With an ambient potassium concentration of 2.5 mM, collecting tubules obtained from the inner stripe of the outer medulla of KD animals absorbed significantly less total CO2 than control tubules. The same tendency was observed in collecting tubules from the outer stripe of the outer medulla. Plasma aldosterone levels fell with development of potassium depletion. Administration of deoxycorticosterone for 1 day to KD animals was associated with a lower urine pH and higher arterial blood pH than in untreated KD animals and with increased total CO2 absorption by both cortical collecting tubules and tubules from the inner stripe of the outer medulla.(ABSTRACT TRUNCATED AT 250 WORDS)
Contribution of AV3V region in anephric NaCl-induced hypertension in the rat
Authors: Haywood J. R. , Ball N. A. , Lifschitz M. D. , Brennan T. J.
Published: December 2017

The role of the anteroventral third ventricle (AV3V) region in mediating hypertonic sodium chloride-induced pressor responses was investigated in conscious rats. Sham- and AV3V-lesioned rats were prepared with femoral artery and vein catheters and subjected to bilateral nephrectomy under gaseous anesthesia. After recovery, animals were infused intravenously with isotonic (0.5 meq/kg) or hypertonic (10 meq/kg) saline at a rate of 0.0103 ml/min over 2 h. Isotonic saline infusion did not affect arterial pressure or heart rate in either group of rats. Hypertonic saline increased arterial pressure 35 +/- 3 mmHg in sham-lesioned rats and only 10 +/- 4 mmHg in AV3V-lesioned animals (P less than 0.0005). Sham-lesioned rats infused with hypertonic saline had a greater vasopressin-dependent component maintaining arterial pressure than the other groups of rats. Conversely, the sympathetic nervous system-dependent component of blood pressure was suppressed in the hypertonic saline-infused sham-lesioned animals compared with the other animals. However, when the vasopressin receptors were blocked, the neurally mediated portion of blood pressure was similar in all four groups of rats. These results emphasize that circulating vasopressin is important for the rise in arterial pressure accompanying the osmotic stimulus. Furthermore, this study demonstrates that the AV3V region is necessary for vasopressin-dependent pressor responses caused by an osmotic stimulus.
Neuropeptide Y inhibits renin release by a pertussis toxin-sensitive mechanism
Authors: Hackenthal E. , Aktories K. , Jakobs K. H. , Lang R. E.
Published: December 2017

The effects of neuropeptide Y (NPY) were studied in the isolated rat kidney, which was perfused at constant perfusion pressure with a synthetic medium. In this preparation NPY produced concentration (1-100 nM)-dependent inhibition of renin release and vasoconstriction. In kidneys perfused at constant flow, inhibition of renin release by NPY was even more pronounced, excluding a flow-dependent washout effect. The simultaneous infusion of the calcium channel antagonist methoxyverapamil (2 microM) or of the calmodulin inhibitor calmidazolium (1 microM) did not prevent these effects of NPY, suggesting that calcium-dependent reactions are not primarily involved. Inhibition of renin release by NPY was also observed in tissue pieces prepared from the hydronephrotic rat kidney, in which tubular elements are lacking. This indicates that inhibition of renin release by NPY is not dependent on the presence of macula densa cells or on changes of intrarenal hemodynamics. In isolated kidneys from rats pretreated with pertussis toxin (2 micrograms/100 g ip) both effects of NPY, renal vasoconstriction and inhibition of renin release, were almost completely abolished. The pertussis toxin-sensitive factor mediating the effects of NPY is most likely the Ni-coupling protein of the adenylate cyclase complex. Accordingly, our data suggest that NPY induces renal vasoconstriction and inhibits renin release by inhibition of adenylate cyclase activity in vascular smooth muscle and renin-producing cells.
cGMP mediates effects of atrial peptides on medullary collecting duct cells
Authors: Zeidel M. L. , Silva P. , Brenner B. M. , Seifter J. L.
Published: December 2017

Atrial natriuretic peptides (ANP) stimulate renal Na+ excretion by poorly understood mechanisms, possibly involving direct inhibition of Na+ transport in the renal medulla. We have previously shown that human ANP 4-28 (hANP) inhibits Na+ entry-dependent O2 consumption (QO2) in rabbit inner medullary collecting duct (IMCD) cells. Because ANP actions in other tissues appear to be mediated by guanosine 3',5'-cyclic monophosphate (cGMP), the present studies examined the role of cyclic nucleotides in IMCD cell responses to ANP. 8-Bromo-cGMP (8-BrcGMP) diminished QO2 by 23.5 +/- 1.2% (SE) in IMCD cells but had no effect in cells derived from outer medullary collecting duct (OMCD); dibutyryl-adenosine 3',5'-cyclic monophosphate (cAMP) was without effect in IMCD cells. The inhibitory effect of BrcGMP was not additive with ANP, amiloride, or ouabain. Amphotericin, which enhances Na+ entry into cells, prevented the inhibitory effect of 8-BrcGMP. These results indicate that 8-BrcGMP, like ANP, inhibited Na+ entry in IMCD cells. hANP stimulated a 10-fold increase in cGMP in IMCD cells without altering IMCD cAMP levels or OMCD cGMP levels. Isobutyl methylxanthine, which inhibits phosphodiesterase activity, enhanced both cGMP accumulation and inhibition of QO2 by submaximal levels (10(-9) M) of ANP. Nitroprusside raised cGMP levels in both IMCD and OMCD cells but inhibited QO2 only in IMCD cells. We conclude that cGMP mediates the transport effects of ANP in IMCD cells. Our results indicate that cGMP may play an important role in the regulation of sodium transport in renal epithelia.
In vivo demonstration of glomerular PGE2 responses to physiological manipulations and experimental agents
Authors: Schlondorff D. , Aynedjian H. S. , Satriano J. A. , Bank N.
Published: December 2017

Experiments were carried out in rats to determine whether prostaglandin E2 (PGE2) synthesized in vivo by individual glomeruli could be measured in fluid obtained from early proximal tubule convolutions. A newly developed nonradioactive enzyme-linked immunoassay for PGE2, capable of measuring 0.1- to 0.25-pg quantities, made this approach feasible. In salt-deprived rats, recollection micropuncture samples were obtained from the earliest proximal convolution [tubular fluid-to-plasma insulin ratio (TF/PIn) 1.13] for measurement of PGE2, and then single-nephron glomerular filtration rate (SNGFR). PGE2 was also measured in serum ultrafiltrate, and theoretical maximum "filtered" PGE2 was calculated for each nephron. This was compared with the measured PGE2 from the same nephron. Indomethacin was then given to inhibit cyclooxygenase. We found that measured PGE2 in early proximal fluid (TF) was higher than could be attributed to glomerular filtration. Indomethacin markedly decreased measured PGE2 in early TF. Administration of probenecid, to block tubular transport of PGE2, did not alter the observations. In chronically salt-loaded rats early TF PGE2 was significantly less compared with the salt-deprived rats. Intrarenal infusion of a nonpressor dose of angiotensin II (ANG II) doubled PGE2 appearance in early TF samples. We conclude from these observations that PGE2 in early TF is derived in part from the glomerulus. In the intact rat, glomerular PGE2 synthesis is higher after salt deprivation than after salt loading, inhibited by indomethacin, and stimulated by ANG II. This new approach will allow evaluation of the role of in vivo glomerular PGE2 production in various pathophysiological conditions.
Cyclosporine nephrotoxicity: sodium excretion, autoregulation, and angiotensin II
Authors: Kaskel F. J. , Devarajan P. , Arbeit L. A. , Partin J. S. , Moore L. C.
Published: December 2017

Cyclosporine-induced nephrotoxicity (CIN) was studied in rats treated for 7 days with cyclosporine (10 mg x kg-1 x day-1 im) or vehicle (CON). CIN rats displayed characteristic reductions in glomerular filtration (GFR) and renal blood blood flow (RBF), and electron microscopy showed injury to proximal cells. Metabolic studies (7 day) showed significantly lower renal sodium excretion in conscious CIN rats compared with CON. In anesthetized rats at similar blood pressures, nephron GFR (SNGFR) was lower in CIN than CON, but fractional Na reabsorption was similar. In CIN, SNGFR, measured proximally to block flow to the sensing site of tubuloglomerular feedback (TGF) at the macula densa, was not significantly different than distal SNGFR. The rate of distal fluid delivery was significantly lower in CIN than in CON. Inhibition of the renin-angiotensin system (RAS) with captopril (CAP, 10 mg/kg iv), or saralasin (SAR, 0.3 mg x kg-1 x h-1 iv) caused marked arterial hypotension in CIN and a fall in renal vascular resistance (RVR). With arterial pressure controlled, CAP or SAR increased GFR and RBF, and reduced RVR in CIN, but did not reverse the renal deficits compared with similarly treated CON. RBF autoregulation in CIN was impaired between 90 and 140 mmHg but was partially restored by CAP. We conclude that both the filtered load and excretion rate of sodium in CIN are significantly reduced compared with controls, that SNGFR in CIN is not depressed by TGF in response to elevated distal fluid delivery, and that the RAS is not a primarily mediator of the renal vasoconstriction in CIN.