bluuebunny/crossref_metadata_2025 huggingface dataset:
Active tetraethylammonium uptake across the basolateral membrane of rabbit proximal tubule
Authors: Tarloff J. B. , Brand P. H.
Published: December 2017

Tetraethylammonium (TEA) uptake was measured in isolated, nonperfused rabbit S2 proximal tubule segments. The TEA cell-to-bath concentration ratio in bicarbonate-Ringer bathing medium was 10-fold higher than that predicted by passive equilibration according to the basolateral electrochemical potential, indicating that TEA uptake is an active process as reported by previous investigators. Removing bicarbonate and CO2 reduced TEA uptake to 22% of control. When bicarbonate-CO2 was replaced by HEPES-O2 or butyrate-O2, TEA uptake was unaltered, but uptake was inhibited when the major buffer anion was omitted. In the presence of 10(-4) M ouabain and bicarbonate-CO2, the TEA cell-to-bath concentration ratio was reduced to 20% of control. TEA uptake in the absence of bicarbonate and CO2 was unaltered by the addition of 10(-4) M ouabain. TEA uptake was inhibited when the bathing medium contained 0 mM K+ or 2 mM Ba2+. These data 1) demonstrate that active basolateral TEA uptake is dependent on medium buffer capacity and 2) support the concept that a portion of TEA uptake occurs via a passive equilibration pathway.
Prostaglandin E2 and cyclic AMP response to vasopressin in renal medullary tubular cells
Authors: Wuthrich R. P. , Vallotton M. B.
Published: December 2017

Rat renal medullary tubular cells, prepared by collagenase dispersion and hypotonic lysis, were introduced in Teflon chambers for superfusion. Prostaglandin (PG) E2 and cyclic adenosine 5'-monophosphate (cAMP) production was measured in the effluent. Arginine vasopressin (AVP) but not 1-deamino-8-D-arginine vasopressin (dDAVP) (10(-10)-10(-6) M), induced a dose-dependent increase in PGE2 synthesis, whereas AVP and dDAVP produced a similar dose-dependent increase in cAMP synthesis. The Ca2+ ionophore A23187 (10(-6) M) stimulated PGE2 synthesis but not cAMP production. In contrast, forskolin (10(-5) M) stimulated cAMP synthesis without affecting PGE2 generation. The pressor antagonists dEt2AVP and d(CH2)5Tyr(Me)AVP (10(-5) M) completely inhibited the PGE2 response to 10(-8) M AVP, whereas d(CH2)5-D-LeuVAVP (10(-6) M), a mixed pressor-antidiuretic antagonist, inhibited incompletely. dEt2AVP did not significantly affect cAMP synthesis in response to 10(-8) M AVP, whereas d(CH2)5-D-LeuVAVP, and unexpectedly also d(CH2)5Tyr(Me)AVP, were inhibitory. dPTyr(Me)AVP (10(-7) M), a pressor antagonist, had an unexpectedly high cAMP-stimulating capacity. In Ca2+-free media containing EGTA, the PGE2 response to AVP and A23187 was inhibited. Nifedipine (10(-6) M) did not significantly inhibit the AVP-stimulated PGE2 production. Thus AVP-stimulated PGE2 synthesis is linked to a V1-receptor in renal medullary tubular cells and occurs independently to the activation of adenylate cyclase through a V2-receptor.
Analysis of renal function in the two-kidney Goldblatt model
Authors: Gabbai F. B. , Gushwa L. C. , Peterson O. W. , Wilson C. B. , Blantz R. C.
Published: December 2017

We analyzed the renal functional responses in all rats 4-6 wk after application of a clip to one renal artery and maintained on either a normal NaCl-intake or a NaCl-depletion protocol utilizing both clearance methods and micropuncture evaluations of glomerular hemodynamics. Although mean arterial pressure (MAP) rose significantly, the response was quite variable and the frequency and degree of hypertension independent of NaCl dietary protocol (142 +/- 7 vs. 137 +/- 6 mmHg, NS). Glomerular filtration rate (GFR) of the unclipped kidney was well maintained regardless of absolute MAP, however, GFR in the clipped kidney was somewhat MAP dependent. The glomerular ultrafiltration coefficient (LpA) was reduced in all clipped rats independent of MAP and dietary NaCl (0.037 +/- 0.002 vs. 0.063 +/- 0.009 nl X s-1 X mmHg-1, P less than 0.05). Glomerular capillary hydrostatic (PG) and glomerular capillary hydrostatic gradient (delta P) were elevated in all clipped rats, regardless of MAP, and to a greater extent in clipped rats maintained on the NaCl-depletion protocol (PG, 59.6 vs. 53.2, P less than 0.05). Among clipped rats, multiple regression analysis revealed no correlation between PG or delta P and the degree of reduction in LpA. The unclipped kidney of the two-kidney, one-clip model is characterized by uniform reductions in LpA independent of the MAP and awake blood pressure produced. Although the increase in PG and delta P may contribute to the reduction in LpA observed, the degree of LpA reduction is independent of the magnitude of elevation in PG and delta P in clipped rats.
cAMP-associated inhibition of Na+-H+ exchanger in rabbit kidney brush-border membranes
Authors: Weinman E. J. , Shenolikar S. , Kahn A. M.
Published: December 2017

Adenosine 3',5'-cyclic monophosphate (cAMP) inhibits the rate of bicarbonate reabsorption and the rate of Na+-H+ exchange transport in the apical membrane of the proximal convoluted tubule. To study the relation between cAMP, cAMP-dependent protein kinase, and Na+-H+ exchange transport, brush-border membrane vesicles from the rabbit kidney were phosphorylated in vitro. The rate of proton gradient-stimulated amiloride-inhibitable 22Na+ uptake was measured as an index of Na+-H+ exchange transport activity. The inclusion of cAMP (10(-6) M) in a phosphorylating solution containing ATP decreased the 10-s uptake of amiloride-sensitive sodium from 2.25 +/- 0.21 nmol/mg protein in controls to 1.94 +/- 0.19 (P less than 0.001). Incubation of vesicles in the presence of purified catalytic subunit of cAMP-dependent protein kinase inhibited the amiloride-sensitive uptake of 22Na+ at 10 s from 2.35 +/- 0.49 nmol/mg protein to 2.05 +/- 0.44 (P less than 0.005). The inhibitory effect of both cAMP and catalytic subunit of cAMP-dependent protein kinase was blocked by the specific thermostable protein inhibitor of the kinase. These studies demonstrate that activation of endogenous membrane-bound cAMP-dependent protein kinase or exposure to exogenous catalytic subunit of cAMP-dependent protein kinase inhibits the rate of Na+-H+ exchange transport in the brush-border membrane of the rabbit kidney.
NH3 and NH4+ transport by rabbit renal proximal straight tubules
Authors: Garvin J. L. , Burg M. B. , Knepper M. A.
Published: December 2017

Isolated perfused S2 proximal straight tubules from rabbits spontaneously secreted ammonia (-1.34 pmol X mm-1 X min-1) and absorbed bicarbonate (49.3 pmol X mm-1 X min-1) when perfusate and bath solutions contained 1 mM NH4Cl and 25 mM bicarbonate (pH 7.4). The NH3 concentration in the collected fluid was on average 40% lower than that of the bath as a consequence of a lower pH in the lumen. To test whether diffusion of NH3 down the bath-to-lumen NH3 concentration gradient could account for the measured ammonia secretion, we measured the permeabilities to NH3 (1.6 X 10(-2) cm/s) and NH4+ (4.5 X 10(-5) cm/s). From these values, we calculated predicted rates of passive NH3 secretion (-3.6 pmol X mm-1 X min-1) and passive NH4+ absorption (0.9 pmol X mm-1 X min-1). The predicted rate of net ammonia secretion exceeded the measured rate, indicating that passive NH3 secretion can fully account for the measured flux. In additional experiments, 10(-4) M acetazolamide in bath and perfusate inhibited net bicarbonate absorption by approximately 80%, but the rate of ammonia secretion was unaffected. Conclusions: S2 proximal straight tubules spontaneously secrete ammonia as required for generation of a corticomedullary ammonia concentration gradient by counter-current multiplication. Diffusion of NH3 down a concentration gradient created by luminal acidification can account for the ammonia secretion. A substantial passive lumen-to-bath backflux of NH4+ occurs. Acetazolamide does not inhibit ammonia secretion.
Adaptation to metabolic acidosis by turtle urinary bladder
Authors: Wheeler R. P. , Arruda J. A.
Published: December 2017

We utilized the turtle urinary bladder to study the mechanisms responsible for adaptation to metabolic acidosis. Bladders removed from acidotic turtles had a higher rate of H+ secretion in vitro than bladders from control turtles, despite identical extracellular pH. HCO3 secretion, however, was not different between the two groups. The increase in H+ secretion could be mediated by a decrease in intracellular pH and/or by an increase in the number of cells thought to be responsible for H+ secretion. To study this issue, we measured intracellular pH with the fluorescent dye 6-carboxyfluorescein diacetate and quantified the number of cells by fluorescence microscopy utilizing acridine orange, rhodamine 123, and 6-carboxyfluorescein diacetate in turtles receiving different acid loads. Urinary acidification measured in vivo was increased in turtles fed a low-acid load for 48 h and in turtles fed a high-acid load for 24-48 h. Intracellular pH was lower in bladders from turtles fed a high-acid load for 48 h but it was not different from controls in the other groups, indicating that intracellular pH cannot account for the adaptive increase in H+ secretion. Bladders from all groups fed an acid load had a higher number of cells with positive staining for acridine orange compared with controls. Double labeling with acridine orange and the mitochondrial stain rhodamine 123 or 6-carboxyfluorescein showed a significant increase in the number of mitochondria-rich cells between control and bladders from turtles fed an acid load. The increase in the number of rhodamine 123- or 6-carboxyfluorescein-positive cells was lower than the increase in acridine orange-positive cells, suggesting that the apparent increase in the number of acridine orange-positive cells is due to an increase in the number of acidic vesicles in the mitochondria-rich cells and in the granular cells rather than solely to an increase in the number of mitochondria-rich cells. Plasma membrane fraction prepared from control and acidotic bladders failed to disclose an increase in the putative H+-ATPase as assessed by enzymatic activity and transport studies. In conclusion, the present study suggests that the adaptive increase in H+ secretion in metabolic acidosis is associated both with an increase in the number of mitochondria-rich cells as well as with an increase in the number of acidic vesicles in these cells.
The kidney in potassium depletion. II. K+ handling by the isolated perfused rat kidney
Authors: Hayashi M. , Katz A. I.
Published: December 2017

In a companion paper we reported a large increment in Na+-K+-ATPase activity and [3H]ouabain binding in the inner stripe of outer medullary collecting tubules from K-depleted rats. To test the hypothesis that the increased number of Na+-K+ pumps in these animals may be involved in potassium reabsorption we examined the effect of ouabain on K excretion by isolated, perfused kidneys from rats fed a K-free diet for 3 wk. Kidneys from K-depleted rats retain potassium avidly, both the fractional (FEK) and absolute K excretion being approximately fivefold lower than in control kidneys. Ouabain (5 mM) increased FEK in kidneys from each K-depleted rat [mean from 8.5 to 34.4%, P less than 0.001, at average (4.5 mM) perfusate K]; similar results were obtained when kidneys were perfused with low (approximately 2 mM) and high (greater than or equal to 8 mM) potassium concentrations. In contrast, ouabain produced a variable effect in control kidneys, that depended on the perfusate potassium concentration. In K-depleted rats amiloride (10(-4) M) did not significantly alter K excretion and did not block the ouabain-induced kaliuresis, suggesting that the latter is not due to enhanced secretion secondary to increased distal fluid delivery. These results provide evidence for ouabain-sensitive potassium reabsorption in kidneys of chronically K-depleted rats, and suggest an explanation for the increased Na+-K+-ATPase observed in such animals.
Calcitonin inhibits Na+ gradient-dependent phosphate uptake across renal brush-border membranes
Authors: Yusufi A. N. , Berndt T. J. , Murayama N. , Knox F. G. , Dousa T. P.
Published: December 2017

This study was undertaken to determine whether calcitonin inhibits Na+-(Pi) cotransport across luminal brush-border membrane (BBM) of proximal tubules. Further, we determined the relative inhibitions of inorganic phosphate (Pi) transport in BBM vesicles (BBMV) derived from superficial cortical tissue (BBMV-SC) and juxtamedullary tissue (BBMV-JM). The effects of maximally phosphaturic doses of calcitonin were compared with those of parathyroid hormone (PTH). Experiments were performed in acutely thyroparathyroidectomized (TPTX) rats fed either normal (NPD, 0.7%) or low (LPD, 0.07%) Pi diets. After measurement of the fractional excretion of phosphate (FEPi) by clearance, the BBMV-SC and BBMV-JM were prepared from kidneys of the same animals and uptakes of 32Pi were determined. Both calcitonin and PTH inhibited BBMV transport of Pi to a greater degree in BBMV-JM than in BBMV-SC, in rats fed NPD or LPD. Kinetic analysis shows that administration of calcitonin resulted in marked decrease of apparent Vmax for Pi without any changes in apparent Km for Pi. However, in spite of a decreased capacity for Na+ gradient-dependent 32Pi uptake in BBMV-JM and much lesser in BBMV-SC in response to administration of calcitonin and PTH in Pi-deprived rats, these phosphaturic peptides did not increase FEPi. We conclude that calcitonin administration decreases the capacity for Na+-Pi cotransport across BBM in proximal tubules of the acutely TPTX rat.
Ontogeny of renal hemodynamic response to renal nerve stimulation in sheep
Authors: Robillard J. E. , Nakamura K. T. , Wilkin M. K. , McWeeny O. J. , DiBona G. F.
Published: December 2017

The renal hemodynamic response to direct electrical stimulation of renal nerves was studied in conscious and chronically instrumented fetal (130-142 days gestation; term 145 days), newborn (7-12 days postnatal), and adult nonpregnant sheep. Renal nerve stimulation (RNS) produced a significant decrease in renal blood flow (RBF) velocity and a significant increase in renal vascular resistance (RVR) in all three groups of animals. The overall decline in RBF velocity and the overall rise in RVR was less pronounced in fetal than in adult sheep (P less than 0.05). Changes in RBF velocity and RVR using an RNS frequency of 16 Hz were -35 +/- 4 and 81 +/- 19% in fetal sheep, -61 +/- 10 and 374 +/- 128% in newborn lambs, and -84 +/- 12 and 540 +/- 94% in adult sheep, respectively. RNS during intrarenal infusion of the alpha-adrenoceptor antagonist phentolamine was associated with a significant increase in RBF velocity and decrease in RVR in both fetal sheep and newborn lambs, but not in adult sheep. Moreover, it was found that the rise in RBF velocity and the decrease in RVR associated with RNS during alpha-adrenoceptor antagonism were completely inhibited by intrarenal infusion of ICI 118,551, a beta 2-adrenoceptor antagonist and unaffected by either cholinergic or dopaminergic antagonists. Taken together, these results suggest that the overall renal vasoconstrictor response to RNS is age dependent. Furthermore, the present results demonstrate that, contrary to observations made in adult animals, RNS can produce renal vasodilation in immature animals that is mediated by beta 2-adrenoceptors.
Adrenergic and angiotensin II influences on renal vascular tone in chronic sodium depletion
Authors: Tucker B. J. , Mundy C. A. , Blantz R. C.
Published: December 2017

To examine the role of adrenergic activity on the reduction in nephron filtration rate during chronic sodium depletion in rats, we have measured all the determinants of glomerular ultrafiltration before and after acute unilateral renal denervation. We also examined whether this adrenergic influence was angiotensin II mediated by performing the same protocol with the addition of systemic infusion of an angiotensin-converting enzyme inhibitor, MK 421. The results indicate that both angiotensin II and adrenergic activity contribute to the maintenance of renal vascular resistance during chronic sodium depletion. Acute renal denervation restored nephron filtration rate in chronic sodium-depleted rats (27 +/- 1 to 32 +/- 2 nl/min, P less than 0.05) to control levels (33 +/- 1 nl/min) via reductions in afferent and efferent arteriolar resistances, which also increased nephron plasma flow (85 +/- 5 to 109 +/- 6 nl/min, P less than 0.05). Infusion of MK 421 also increased plasma flow in chronic sodium-depleted rats (116 +/- 11 nl/min, P less than 0.05) through decreases in both arteriolar resistances. Denervation in MK 421-treated rats further increased nephron plasma flow to 137 +/- 10 nl/min (P less than 0.05) only as a result of decreased afferent resistance. The findings indicate that the glomerular hemodynamic changes that characterize chronic sodium depletion are primarily due to the activity of angiotensin II. However, renal adrenergic activity contributes an independent effect on afferent resistance and an effect on efferent resistance via adrenergic effects on angiotensin II.
Superficial nephron responses to peritubular capillary infusions of angiotensins I and II
Authors: Mitchell K. D. , Navar L. G.
Published: December 2017

Proximal tubular reabsorption, stop-flow pressure (SFP), and single nephron glomerular filtration rate (SNGFR) were measured in the absence of and during infusion of an isotonic saline solution containing either angiotensin I (ANG I; 10(-6) to 10(-5) M) or angiotensin II (ANG II; 10(-9) to 10(-7) M) into an adjacent peritubular capillary at a rate of 20 nl/min. Dilution of the infused ANG I and ANG II occurred in the peritubular capillary blood and as the peptides diffused into the interstitium. Infusion of either 10(-7) M ANG II or 10(-5) M ANG I increased proximal fractional fluid reabsorption (FRH2O) and decreased both SFP and SNGFR. There were no significant changes in FRH2O or SNGFR during infusion of 10(-5) M ANG I when the converting enzyme inhibitor enalaprilat (MK 422, 10(-3) M) was added to the infusate. Similarly, peritubular infusion at lower concentrations of either ANG II (10(-9) or 10(-8) M) or ANG I (10(-6) M) did not alter FRH2O, SFP, or SNGFR. These data indicate that conversion of ANG I to ANG II can occur in the peritubular capillary or interstitial environment and that increases above the normal endogenous levels in the postglomerular interstitial ANG II concentration can enhance proximal tubular reabsorption and increase preglomerular resistance and thereby reduce SNGFR.
Renal clearance of glutathione measured in rats pretreated with inhibitors of glutathione metabolism
Authors: Scott R. D. , Curthoys N. P.
Published: December 2017

Renal clearance measurements were performed in rats pretreated with various inhibitors of glutathione metabolism. Approximately 97% of the renal gamma-glutamyltranspeptidase was inactivated by infusion of AT-125. Within 4.5 h arterial plasma concentration and urinary excretion of glutathione increased from 4 microM and 1.2 nmol/h to 27 microM and 3,900 nmol/h, respectively. The ratio of excreted to filtered glutathione increased from less than 0.01 to 1. When renal glutathione was decreased to 35% of normal by pretreating rats with D,L-buthionine-S,R-sulfoximine, the subsequent inactivation of the transpeptidase caused only a two-fold increase in arterial plasma glutathione, and urinary excretion increased to only 70% of the filtered load. The filtered load of glutathione was reduced by intravenous infusion of purified gamma-glutamyltranspeptidase. At 1 to 3 h after infusion, arterial glutathione decreased to 0.3 microM. Under these conditions, the amount of glutathione excreted by an AT-125-treated rat was 40-fold greater than the filtered load. When similar experiments were carried out in rats that were pretreated with D,L-buthionine-S,R-sulfoximine and AT-125, urinary excretion of glutathione was decreased 10-fold, but it still exceeded the amount filtered. These results firmly establish that apical secretion contributes to the glutathione catabolized in the tubular lumen.
Metabolic aspects of the regulation of systemic pH
Authors: Atkinson D. E. , Bourke E.
Published: December 2017

Catabolism of protein produces CO2, NH4+, and HCO3-. Mammals readily lose CO2 through the lungs, but the bicarbonate produced in metabolism of a typical diet (in humans, approximately 1 mol/day from approximately 100 g of protein) would cause alkalosis if not disposed of. Air-breathing animals solve this problem by incorporating NH4+ into organic compounds in which N is not protonated; thus each NH4+ ion loses a proton in the course of the synthesis. These protons serve to titrate HCO3-. In mammals, ureagenesis is the pathway by which protons are liberated from NH4+. The rate of ureagenesis therefore determines the rate of disposal of bicarbonate, and must be an important factor in the maintenance of pH homeostasis. Ammonium ion that is not needed for urea synthesis is packaged into glutamine by the liver. Hepatic glutamine synthetase is localized in the last rank of cells around the pericentral venule; thus glutamine synthetase cannot compete for NH4+ or interfere with the control of pH by urea synthesis. Ammonium excretion in the urine does not represent excretion of acid, and is not stoichiometrically related to renal generation of bicarbonate. The quantitatively major processes by which the HCO3-/CO2 ratio, and hence the pH, is regulated in blood and interstitial fluid are excretion of CO2 through the lungs and disposal of HCO3- as a consequence of ureagenesis in the liver.
Effect of vasopressin analogue (dDAVP) on potassium transport in medullary collecting duct
Authors: Sonnenberg H. , Honrath U. , Wilson D. R.
Published: December 2017

The microcatheterization technique was used to examine electrolyte transport in the medullary collecting duct of two groups of anesthetized rats during water diuresis and during a second experimental phase with 1-desamino-8-D-arginine vasopressin (dDAVP) administration or continued water diuresis. Potassium reabsorption of 53-61% of the delivered load was consistently observed in the medullary collecting duct during water diuresis. During dDAVP administration, urinary potassium excretion doubled, and there was no net potassium transport (reabsorption or secretion) in the medullary collecting duct. The change in potassium transport in medullary collecting duct from water diuresis to antidiuresis (dDAVP) was sufficient to account for the increase in urinary potassium excretion. Changes in flow rate, luminal sodium concentration, or collecting duct sodium reabsorption could not account for the changes in potassium transport in the collecting duct during dDAVP. The results are interpreted as indicating that dDAVP stimulates potassium entry (secretion) into the medullary collecting duct, probably by a direct effect. This action of antidiuretic hormone appears to be important in maintaining potassium homeostasis during changing water balance.
Renal effects of endotoxin in the male rat
Authors: Churchill P. C. , Bidani A. K. , Schwartz M. M.
Published: December 2017

A new model of acute reduction in renal function induced by a 2-h infusion of endotoxin (Escherichia coli 026:B6 lipopolysaccharide, 5 mg X kg-1 X h-1) was developed in the anesthetized male rat. In the absence of significant glomerular fibrin deposition, inulin clearance (glomerular filtration rate, GFR) was reduced from 8.50 +/- 0.34 to 4.01 +/- 0.45 ml X kg-1 X min-1 (P less than 0.0005), and p-aminohippuric acid clearance was reduced from 23.7 +/- 0.8 to 15.0 +/- 1.8 ml X kg-1 X min-1 (P less than 0.0005), indicating a hemodynamic basis for the reduction in GFR. The lack of morphological tubular injury and a decreased fractional Na excretion (from 2.63 +/- 0.27 to 0.54 +/- 0.09%, P less than 0.00005) exclude a significant contribution of tubular mechanisms to the reduction in GFR. Administration of theophylline, a competitive adenosine receptor antagonist, concurrently with or immediately after the endotoxin infusion, restored inulin and PAH clearances and fractional Na excretion toward normal. Moreover, the renal effects of endotoxin were mimicked by intravenous administration of N6-(L-phenylisopropyl)-adenosine (L-PIA), an adenosine receptor agonist, and the effects of L-PIA in turn were also antagonized by theophylline. These data suggest that adenosine plays a significant role in mediating the hemodynamic derangements of this model.
Modulation of albuminuria by dietary protein and converting enzyme inhibition
Authors: Hutchinson F. N. , Schambelan M. , Kaysen G. A.
Published: December 2017

Both dietary protein restriction and angiotensin converting enzyme inhibitors (CEI) reduce proteinuria in experimental renal disease. To determine whether the effects of dietary protein on albuminuria (UalbV) in nephrotic rats are modified by CEI, we measured UalbV and glomerular filtration rate (GFR) in rats with passive Heymann nephritis fed 40 (HP) or 8.5% (LP) protein diets. Half of each group received enalapril beginning 2 days after injection of antibody. Enalapril prevented the greater UalbV and fractional clearance of albumin (FCalb) observed in HP (HP + enalapril, 136+/- 44 mg/day and 0.88+/- 0.54 X 10(-2), vs. HP, 368+/- 60 mg/day and 4.40+/- 2.90 X 10(-2), P less than 0.05 and P less than 0.05, respectively) but did not alter GFR significantly. Enalapril did not alter UalbV or FCalb in LP. To determine if CEI would reduce UalbV in rats after proteinuria was already present, rats fed 21% protein were studied 1 wk after the onset of proteinuria. Enalapril decreased UalbV (423+/- 35 to 169+/- 18 mg/day, P less than 0.001) and FCalb (3.19+/- 0.36 X 10(-2) to 0.71+/- 0.11 X 10(-2), P less than 0.001) after 3 days. Thus CEI reduced albuminuria in nephrotic rats fed high- or normal-protein diets without modifying GFR or serum albumin. This effect may be due to changes in glomerular hemodynamics or permselectivity.
Role of prostaglandin in norepinephrine and renin release in canine kidney
Authors: Hayashi Y. , Hisa H. , Satoh S.
Published: December 2017

We investigated renin and norepinephrine (NE) release during electrical renal nerve stimulation (RNS) in relation to prostaglandin (PG) E2 concomitantly produced by the kidney in anesthetized dogs. During 10 min of continuous RNS (2.5-4 Hz), the increases in renin, NE, and PGE2 secretion rates were determined at 1 and 10 min after the start of stimulation. Under control conditions, almost the same extent of increase in the NE secretion rate was observed at 1 and 10 min of RNS, whereas the increase in renin secretion rate at 1 min of RNS was followed by a further increase at 10 min of RNS. On the other hand, an upward but not significant trend of increase in PGE2 secretion at 1 min of RNS was followed by a substantial level at 10 min of RNS. After administration of indomethacin, the increase in NE secretion rates at both 1 and 10 min of RNS were not altered, but the increase in renin secretion rate at 10 min of RNS was suppressed by approximately 50%, without any reduction of the increase in the renin secretion rate at 1 min of RNS. Consequently, the time-related change in the renin secretion rate during RNS was abolished. These results suggest that renin response to continuous RNS is enhanced by concomitantly generated PGs but not by NE, and furthermore, that endogenously generated PGs do not inhibit the release of NE from canine renal nerve endings.
Lysosome distribution and cathepsin B and L activity along the rabbit proximal tubule
Authors: Madsen K. M. , Park C. H.
Published: December 2017

The lysosomal-vacuolar system in the proximal tubule is responsible for reabsorption and degradation of proteins from the glomerular filtrate. In this study we mapped the activity of the lysosomal proteinases, cathepsins B and L, along the rabbit proximal tubule and compared cathepsin activities with the volume of lysosomes and endocytic vacuoles in the three segments of the proximal tubule. Individual tubules were dissected and assayed fluorometrically using two synthetic substrates, one specific for cathepsin B and a second for cathepsins B and L. The distribution of cathepsin activity along the proximal tubule was the same with each substrate, but there was a two- to threefold difference in the level of activity when expressed per millimeter of tubule. Enzyme activities were high in the initial 4-5 mm corresponding to the S1 segment and decreased in the pars recta to approximately 20% of the S1 value. Morphometric analysis revealed that the volumes of lysosomes and endocytic vacuoles per millimeter of tubule were significantly greater in the S1 segment than in the S2 and S3 segments. These findings suggest that the main site of protein degradation in the rabbit kidney under normal conditions is the initial 4-5 mm of the proximal tubule which corresponds to the S1 segment and is known to be a major site of protein reabsorption.
Indomethacin and patent ductus arteriosus: effects on renal function in preterm lambs
Authors: Gleason C. A. , Clyman R. I. , Heymann M. A. , Mauray F. , Leake R. , Roman C.
Published: December 2017

To examine the independent effects of a patent ductus arteriosus and of indomethacin therapy on the renal function of the preterm newborn, we created a preterm lamb model in which ductus diameter could be regulated. We studied 24 preterm newborn lambs. Eight lambs (group 1) had their ductus closed at delivery and received no indomethacin. Eight lambs (group 2) had their ductus closed and then received indomethacin (0.3 mg/kg) at 5.5 h; eight lambs (group 3) had their ductus kept open and then received indomethacin at 5.5 h. Hemodynamic and renal function measurements were made at 5 h (pretreatment) and at 12.5 h. In group 2 lambs there was a significant reduction in inulin clearance (GFR) and osmolal clearance after indomethacin. In contrast, lambs with an open ductus (group 3), when compared with lambs with a closed ductus (groups 1 and 2) at 5 h, already had significantly decreased blood pressure, GFR, urine volume, and osmolal clearance. Following indomethacin treatment, group 3 lambs showed no further decrease in renal function. We suggest that in preterm lambs with patent ductus, the apparent lack of renal dysfunction following indomethacin treatment reflects underlying diminished renal function.
Contribution of dopamine 2 receptors to dopamine-induced increase in glomerular filtration rate
Authors: Seri I. , Aperia A.
Published: December 2017

The effects of the interaction of dopamine (DA) and the DA2 receptors on glomerular filtration rate (GFR) has been studied by means of micropuncture technique in adult greater than or equal to 60-day-old and young 24-day-old rats. Most of the studies were performed in rats with intact adrenergic nervous systems to allow for evaluation of the presynaptic DA2 receptors. In adult and young rats, DA and LY-171555 (LY), a selective DA2 receptor agonist, induced prompt and significant increases in the single nephron (SN) GFR. Further studies were performed only in adult rats. The LY-induced increase in SNGFR was completely abolished during DA2 receptor blockade with S-sulpiride (S-SP), while the DA-induced increase in SNGFR was attenuated but still significant during S-SP treatment. Both DA and LY significantly increased the glomerular ultra-filtration pressure (PUFAA). In rats with ganglionic blockade, the LY-induced increase of SNGFR was attenuated but still significant, whereas the DA-induced increase was less affected. The results imply that DA significantly increases GFR by interacting with the DA2 as well as with the DA1 receptors. Interaction between DA and the DA2 receptors increases PUFAA. The results do not rule out the existence of both pre- and postsynaptic renal DA2 receptors.
Loss of renal blood flow autoregulation in chronic glomerulonephritic rats
Authors: Iversen B. M. , Ofstad J.
Published: December 2017

Autoregulation of renal blood flow (RBF) was investigated in subacute (2 mo) and chronic (18 mo) passive Heymann nephritis (PH-2, PH-18) and age-matched controls (C-2, C-18). RBF was significantly lower in PH-18 than in C-18 (3.7 +/- 0.4 vs. 4.7 +/- 0.5 ml.min-1.kidney-1; P less than 0.05), whereas the mean blood pressure (MAP) was similar. The creatinine clearance was significantly lower in PH-18 than in C-18 (1.89 +/- 0.5 vs. 3.15 +/- 0.77 ml.min-1.kg body wt-1; P less than 0.002). Kidney weight was significantly higher in PH-18 than in C-18 (P less than 0.002). In PH-2 and C-2, RBF, MAP, creatinine clearance, and kidney weight were not different (P greater than 0.10). In PH-18 the maximal reduction of the renal vascular resistance (RVR) during RBF autoregulation was 4 +/- 2%, compared with 24 +/- 4% in C-18 (P less than 0.002); the lower pressure limit of RBF autoregulation was 131 +/- 9 vs. 85 +/- 4 mmHg (P less than 0.002). In PH-2 the maximal reduction of RVR during RBF autoregulation was 18 +/- 3%; in C-2 it was 25 +/- 2% (P greater than 0.10); the lower pressure limit of RBF autoregulation was 101 +/- 4 vs. 84 +/- 6 mmHg (P less than 0.02). It is concluded that RBF autoregulation is nearly lost in the late stage of glomerulonephritis, possibly as a consequence of the nephron loss.
Metabolic substrate utilization by rabbit proximal tubule. An NADH fluorescence study
Authors: Balaban R. S. , Mandel L. J.
Published: December 2017

The effects of various short-chain fatty acids, carboxylic acids, and amino acids on NADH fluorescence and oxygen consumption (QO2) of rabbit proximal tubule suspensions were determined. The short-chain fatty acids were the most effective substrates in increasing NADH fluorescence and QO2, followed by the carboxylic acids and amino acids. All of the substrates tested that increased NADH fluorescence proportionally increased QO2. This implies that the primary effect of these substrates was to increase QO2 by increasing the delivery of reducing equivalents to NAD and not by stimulating ATP hydrolysis directly. The relative affinity of several substrates to increase NADH fluorescence was also determined. The short-chain fatty acids had the highest affinity (10 microM range) followed by the carboxylic acids (100 microM range). These data demonstrate that the metabolic rate and NADH redox state of the renal cortical cell is very sensitive to the type of metabolic substrate available.
Gentamicin nephrotoxicity in the setting of acute renal hypoperfusion
Authors: Zager R. A.
Published: December 2017

The purpose of this study is to assess interactions between acute renal hypoperfusion and aminoglycoside nephrotoxicity. One hour of renal hypoperfusion (55–60 mmHg; renal blood flow 1.6 +/- 0.13 ml/min) was created in rats by suprarenal partial aortic constriction. Gentamicin, 120 mg/kg, was given at the start of the hypoperfusion period. Rats that either received gentamicin alone or were subjected to hypoperfusion alone served as controls. Hypoperfusion alone induced mild S3 proximal tubular brush-border membrane blebbing, but it caused no enzymuria, azotemia, or tubular necrosis. Gentamicin alone induced no azotemia or tubular necrosis. However, gentamicin injected during hypoperfusion caused severe azotemia (blood urea nitrogen 94 +/- 16; creatinine 1.74 +/- 0.22 mg/dl) and extensive S3 proximal tubular necrosis without affecting renal perfusion. S1 and S2 tubular segments, the major targets of gentamicin toxicity, showed minimal damage. Hypoperfusion increased renal gentamicin uptake, but matching it in control rats induced no renal damage. In conclusion, gentamicin can precipitate hypoperfusion-induced acute renal failure. This effect appears to be due to an S3 cytotoxic effect, which converts sublethal ischemic S3 tubular injury into overt cell necrosis.
Suppression of AVP release by drinking despite hypertonicity during and after gestation
Authors: Davison J. M. , Shiells E. A. , Philips P. R. , Lindheimer M. D.
Published: December 2017

Water drinking suppresses arginine vasopressin (AVP) release before changes in tonicity or volume. To further characterize this oropharyngeal neuroendocrine reflex, we took advantage of ongoing studies of osmoregulation in pregnancy as follows: five women studied serially in early (8 +/- 1 wk, mean +/- SD) and late (32 +/- 3 wk) pregnancy and 8–10 wk postpartum were slowly infused with hypertonic saline for 150 min while drinking water to satiety (drinking started at 120 min). Plasma osmolality (Posmol) at 120 min was increased (277 +/- 3 to 291 +/- 2, 280 +/- 6 to 295 +/- 5, and 287 +/- 1 to 307 +/- 1 mosmol/kg in 1st and 3rd trimesters and postpartum; P less than 0.01), accompanied by increments in plasma AVP (PAVP) up to 7 +/- 5, 5 +/- 3, and 8 +/- 3 pg/ml, respectively (P less than 0.01). PAVP declined as soon as drinking began (P less than 0.01 at 5 min), despite maintenance of peak osmolality for another 30 min. Similar events were recorded in three males. Calculation of normal disappearance rates (t1/2) demonstrated that AVP levels decreased more rapidly (P less than 0.01) in the 3rd trimester compared with early pregnancy and postpartum. Two other subjects became nauseated during their 1st trimester and postpartum tests which permitted comparison of nausea and drinking which evoke central reflexes with opposing action on AVP release. PAVP, which had increased markedly (range 17–42 pg/ml; P less than 0.01), was not abolished by drinking. These data demonstrate the potency of the drinking reflex on osmoregulation in pregnant and nonpregnant subjects.(ABSTRACT TRUNCATED AT 250 WORDS)
Ontogeny of the renal response to natriuretic peptide in sheep
Authors: Robillard J. E. , Nakamura K. T. , Varille V. A. , Andresen A. A. , Matherne G. P. , VanOrden D. E.
Published: December 2017

The ontogeny of the renal response to continuous systemic infusion of atrial natriuretic peptide (ANP) was studied in chronically instrumented fetal, newborn, and adult nonpregnant sheep. Plasma immunoreactive ANP (ANPir) concentrations during low (0.025 microgram.kg-1.min-1) and high rate (0.1 microgram.kg-1.min-1) ANP infusion were similar between each group of animals. Decrease in renal blood flow velocity (RBFV) and rise in renal vascular resistance (RVR) were observed in fetal and newborn lambs during ANP infusion. The percent changes in RBFV and RVR were of significantly (P less than 0.05) greater magnitude during high ANP infusion rate in fetuses (-28.5 +/- 8.5 and 93 +/- 6.4%) than in adult sheep (-6.6 +/- 3.2 and -4.4 +/- 4.9%). ANP produced no changes in urine flow (V) in fetuses but increased V significantly in newborn lambs and adult sheep. Glomerular filtration rate increased significantly during ANP infusion in adult sheep but not in fetal and newborn lambs. Percentage changes in urinary excretion rate of Na (UNaV) during high ANP infusion rate were significantly higher in adult sheep (3,520 +/- 2,414%) than in newborn (157 +/- 106%) and fetal lambs (198 +/- 84%). These results suggest that the cardiovascular, renal hemodynamic, and possibly renal function responses to continuous ANP infusion increase during maturation, the overall response being larger in adult animals.
Origin of ADH-induced vacuoles in rabbit cortical collecting tubule
Authors: Kirk K. L.
Published: December 2017

The origin of the vacuoles that form in the mammalian collecting duct during antidiuretic hormone (ADH)-mediated water reabsorption was examined using two computer-assisted, light microscopic methods. First, differential interference-contrast microscopy was used in combination with a simple morphometric procedure to quantitatively characterize the time course, magnitude, and cell specificity of vacuole formation in the microperfused rabbit cortical collecting tubule. Second, video-intensified fluorescence microscopy was used to visualize the basolateral endocytosis of a fluorescent, fluid-phase marker (i.e., lucifer yellow) during vacuole formation. In the presence of a lumen-to-bath osmotic gradient, ADH addition induced the rapid (less than 10 min) formation of large (1- to 3-micron diam) vacuoles in principal cells and, to a lesser extent, in a subpopulation of intercalated cells. The vacuoles subsequently shrank and disappeared over the course of 60-90 min in the continued presence of the hormone and osmotic gradient. The vacuoles collapsed very slowly after elimination of the osmotic gradient at the peak of the vacuolation response, which implies that these structures are intracellular compartments rather than dilated extracellular spaces. During their formation the vacuoles could be loaded with peritubular (but not luminal) lucifer yellow, which remained trapped within most of these structures well after the dye was removed from the bath (greater than 30 min). These results indicate that most vacuoles that form during ADH-mediated water reabsorption are intracellular, endocytic compartments that communicate with the peritubular space via endocytosis of basolateral cell membrane.
Neurohormonal regulation of renal function during development
Authors: Robillard J. E. , Nakamura K. T.
Published: December 2017

This review summarizes current understanding of fetal renal physiology and considers the role of the neuroadrenergic system and renin-angiotensin system in controlling renal hemodynamics and function during development. Recent evidence suggests that renal innervation appears early during fetal life but is not an important modulator of renal hemodynamics and function during resting conditions in immature animals. It has also been observed that the renal hemodynamic response to renal nerve stimulation (RNS) is less in fetal and newborn animals than in adults. But contrary to previous findings in adult animals, RNS during alpha-adrenoceptor antagonism produces renal vasodilation in fetal and newborn sheep, but not in adult ewes. The role of the renin-angiotensin system (RAS) in modulating renal hemodynamics and function during prenatal and postnatal maturation is discussed. It is suggested that the RAS plays an important role in regulating blood pressure early during fetal life, whereas its influence on renal hemodynamics and function appears later during development.
Hemodynamic and renal responses to volume expansion in dogs with cardiac denervation
Authors: Pichet R. , Gutkowska J. , Cantin M. , Lavallee M.
Published: December 2017

Hemodynamic responses, renal function, and plasma levels of immunoreactive atrial natriuretic factor (irANF) were examined following volume expansion (VE) in normal (N) conscious dogs and in conscious dogs with cardiac denervation (CD). Base-line urine flow was consistently greater (P less than 0.05) in dogs with CD (0.54 +/- 0.06 ml/min) than in N (0.29 +/- 0.03 ml/min) dogs but sodium excretion did not differ between N (2.80 +/- 0.58 mu eq.min-1.kg body wt-1) and CD (3.53 +/- 0.75 mu eq.min-1.kg-1) groups. With VE (18 ml/kg of 3% dextran in saline), mean arterial pressure (MAP) increased (P less than 0.01) by 16 +/- 3 from 103 +/- 4 mmHg in N dogs but did not change from pre-VE base line (103 +/- 2 mmHg) in dogs with CD. At 10 min after VE, urine flow increased more (P less than 0.01) in N dogs (1.39 +/- 0.24 ml/min) than in dogs with CD (0.26 +/- 0.09 ml/min). At that time, increases in sodium excretion were also greater (P less than 0.01) in N (9.13 +/- 1.96 mu eq.min-1.kg-1) dogs than in dogs with CD (1.06 +/- 0.68 mu eq.min-1.kg-1). With VE, increases in irANF plasma levels were not different in N dogs (40 +/- 12 from 34 +/- 5 pg/ml) and in dogs with CD (27 +/- 3 from 45 +/- 7 pg/ml). In dogs with CD, when MAP was increased by aortic constriction to mimic responses observed in N dogs, renal responses were similar to those of N dogs.(ABSTRACT TRUNCATEDAT 250 WORDS)
Influence of flow rate and perfused load on insulin absorption in isolated proximal tubules
Authors: Nielsen S. , Nielsen J. T.
Published: December 2017

The effect of flow rate and perfused load on insulin absorption was studied in isolated proximal rabbit tubules. In one series of experiments tubules were perfused for 30 min with 125I-[A14]insulin at 3.6 ng/ml and at flow rates varying between 2.2 and 43.3 nl/min, thus varying both flow rate and the perfused load. In a second series of experiments the tubules were exposed to increasing loads of insulin at a fixed flow rate of 15 nl/min. In a third series of experiments two groups of tubules were exposed to identical perfused loads at two different flow rates. The results showed that absorption is linearly correlated with the perfused load in the ranges of flow rates and concentrations examined. The perfused load determined the magnitude by which the insulin was reabsorbed, whereas the flow rate determined the efficiency (fractional absorption) by which the protein was reabsorbed. At flow rates less than 5 nl/min the fractional absorption was greater than 65%, and at flow rates greater than 30 nl/min fractional absorption was less than 40%. Thus, there is an inverse relationship between flow rate and fractional absorption. The described effects of changes in flow rate and perfused load are suggested to be caused by concomitant changes in the mean luminal concentration.
Parathyroid hormone mediates changes in calcium transport in uremic rat brain synaptosomes
Authors: Fraser C. L. , Sarnacki P.
Published: December 2017

In previous studies, we showed that Ca2+ transport by both Na+ gradient-stimulated Ca2+ uptake and ATP-stimulated Ca2+ uptake was increased in synaptosomes from uremic rat brain. The possible role of parathyroid hormone (PTH) in this observation was investigated by performing Ca2+ transport studies in synaptosomes by these two mechanisms. Studies were performed in vesicles from rats that were either normal, uremic, uremic parathyroidectomized (PTX-U), or uremic parathyroidectomized but treated with PTH. In uremic rats, transport by both Na+ gradient-stimulated Ca2+ uptake and ATP-stimulated Ca2+ uptake was increased by 30 and 47%, respectively, whereas uptake was returned to base line in synaptosomes from PTX-U rats. Additionally, the administration of PTH to PTX-U rats resulted in a significant increase (P less than 0.001) of 36 and 41%, respectively, above the values observed in PTX-U rats. To determine whether the increased accumulation of Ca2+ in synaptosomes in uremia was a result of PTH alone and/or to the uremic environment, we next performed uptake studies in synaptosomes that were isolated from nonuremic rats that were either normal, parathyroidectomized (PTX) or PTX but treated with 2.8–100 micrograms PTH. By both transport mechanisms, uptake was significantly (P less than 0.01) decreased from normal by 27% in the PTX group, and either 2.8 or 110 micrograms PTH resulted in a significant increase in transport to base line by Na+-gradient stimulated Ca2+ uptake. However, Ca2+ accumulation by ATP-stimulated Ca2+ uptake was significantly increased to base line only with 100 micrograms PTH.(ABSTRACT TRUNCATED AT 250 WORDS)