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PubMed1993

Response of the avian kidney to acute changes in arterial perfusion pressure and portal blood supply.

Domestic fowl kidneys autoregulate total renal blood flow and glomerular filtration rate (GFR) over a wide range of renal arterial perfusion pressure (RAPP). Sustained (approximately 2-4 h) restriction of renal portal blood flow attenuates the autoregulatory responses. The present study was designed to assess the effects of acute (approximately 10 min) alterations of renal portal blood flow on renal function, and to dissociate the renal responses to altered renal portal blood flow from the renal responses to reductions in RAPP. The thermal pulse decay (TPD) technique and p-aminohippuric acid clearance (CPAH) were used to measure blood flow. During acute increases and decreases in renal portal blood flow, regional renal blood flow as measured by the TPD system (RBFTPD) was significantly positively correlated with total kidney blood flow represented by CPAH (RBFPAH). These results indicate that changes in total kidney blood flow induced by alteration of portal perfusion were reflected in the regional measurement of renal blood flow. Changes in renal portal blood flow did not affect the urine flow rate (UFR), GFR, or fractional excretion of sodium (FENa). Reducing RAPP from 120 to 50 mmHg significantly reduced UFR, GFR, and FENa. Overall, these results indicate that large acute changes in renal portal blood flow can significantly alter total renal blood flow without significantly affecting parameters (UFR, GFR, and FENa) primarily influenced by the renal arterial vasculature.

Animals↗

PubMed1994

Control of erythropoiesis in humans during prolonged exposure to the altitude of 6,542 m.

Altitude hypoxia induces an increase in erythropoiesis. Some of the factors involved in the control of altitude polycythemia were studied. Ten subjects (4 women, 6 men) were exposed for 3 wk to extreme altitude (6,542 m). Blood was withdrawn in normoxia (N) and after 1 wk (H1), 2 wk (H2), or 3 wk (H3) at 6,542 m for the measurement of serum erythropoietin (EPO), blood hemoglobin (Hb), hematocrit (Hct), intraerythrocyte folate (Fol), and plasma ferritin (Fer) concentrations. Renal blood flow (RBF) and absolute proximal reabsorption rate (APR) were measured by the p-aminohippuric acid and lithium clearance, respectively, in N and H2 conditions. O2 supply to the kidneys was calculated using RBF and arterial O2 content (CaO2). After an initial sharp increase in EPO, it decreased at H2 and H3. Hct and Hb increased from N to H1 and H2 and then unexpectedly decreased from H2 to H3. Mean corpuscular Hb content (MCHC = Hb/Hct) was lower in all H than in N conditions. Increase in EPO at H1 varied from 3- to 134-fold among individuals. Women showed a smaller increase in Hct and Hb and a greater decrease in MCHC. Two women showed a large increase in EPO without increase in Hb. Fol was not modified by altitude hypoxia. Fer showed a marked decrease in H1 and H3 compared with N. Hb was positively related to Fer in hypoxia. Iron intake in food was markedly decreased during the 2-wk ascent to 6,542 m. EPO was inversely related to CaO2 and positively related to APR.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗

PubMed1995

Urate transport in Homarus americanus hepatopancreas: studies on membrane vesicles and R cells.

[2-14C]urate uptake was studied in hepatopancreatic basolateral membrane vesicles and in R cell suspensions of the American lobster by Millipore filtration techniques. Unspecific binding of urate to the vesicular membrane was 25.5 +/- 3.0% of equilibrium. Vesicular uptake showed a diffusional and a saturable component (Km) 0.37 +/- 0.04 mM and maximal velocity (Vmax) 16.5 +/- 1.2 pmol urate.mg protein-1.s-1). [2-14C]urate uptake was significantly trans-stimulated by urate. Purine analogues, probenecid, p-aminohippuric acid, pyrazinoic, and oxonic acid cis-inhibited urate transport. Urate uptake was not affected by Na+ or K+ transmembrane gradients but stimulated by 1 mM 2-oxoglutarate at the cis-side in Na(+)-containing media. Cellular urate uptake was inhibited by pyrazinoic acid. Uptake was saturable (Km 0.53 +/- 0.11 mM and Vmax 3.7 +/- 0.4 pmol urate.mg protein-1.s-1) and Na(+)-independent. However, 2-oxoglutarate stimulated uptake in Na(+)-containing media. These results suggest that urate uptake across the basolateral membrane occurs via a specific, Na(+)-independent transport system that may operate in the exchange mode accepting 2-oxoglutarate as countertransported substrate. In vivo, urate uptake thereby would be a tertiary active system driven by a 2-oxoglutarate gradient established across the cell membrane by the operation of a Na(+)-2-oxoglutarate cotransport system.

Animals↗

PubMed2006

Increased renal phosphodiesterase-5 activity mediates the blunted natriuretic response to ANP in the pregnant rat.

Normal rat pregnancy is characterized by plasma volume expansion due to renal sodium retention and is associated with a blunted response to natriuretic stimuli, such as atrial natriuretic peptide (ANP). ANP signals via cGMP, and phosphodiesterases (PDE) inactivate cGMP and terminate the natriuretic response. We previously reported that increased medullary PDE-5 activity occurs in rat pregnancy, which may be the mechanism of the blunted natriuretic effect of ANP. Here, we used anesthetized 16-day pregnant and virgin rats to investigate whether intrarenal infusion of a selective PDE-5 inhibitor, sildenafil, would reverse the blunted response to ANP in pregnancy. We measured blood pressure, renal clearances using inulin and p-aminohippuric acid, and electrolyte excretion at baseline and during an ANP infusion. ANP caused a fall in mean arterial pressure in all groups, and sildenafil induced a further reduction. We observed an increase in sodium excretion with ANP in all rats, but this was blunted in the vehicle-infused pregnant rats. This could not be explained by differences in renal hemodynamics and was of tubular origin, as reflected by the reduced rise in fractional excretion of sodium with ANP in the pregnant rat given vehicle (45 +/- 11 vs. 204 +/- 49%; P < 0.05). However, intrarenal sildenafil increased the natriuretic response and the rise in fractional excretion of sodium to the virgin value (226 +/- 23 vs. 245 +/- 73%; not significant), whereas the blunting persisted in the contralateral kidney. This demonstrates that increased intrarenal PDE-5 mediates the blunted natriuretic response to ANP during pregnancy and may contribute to the physiological volume expansion.

3',5'-Cyclic-GMP Phosphodiesterases↗

PubMed2002

Renal arginine and protein synthesis are increased during early endotoxemia in mice.

The kidney has an important function in arginine metabolism, because the kidney is the main endogenous source for de novo arginine production from circulating citrulline. In conditions such as sepsis, nitric oxide (NO) production is increased and is dependent on extracellular arginine availability. To elucidate the adaptive role of renal de novo arginine synthesis in a condition of increased NO production, we studied renal arginine metabolism in a mouse model of endotoxemia. Because arginine flux is largely dependent on protein flux, we also measured protein metabolism in mice. Female mice were injected intraperitoneally with lipopolysaccharide; control mice received 0.9% NaCl. Six hours later, renal blood flow was measured with the use of para-aminohippuric acid. Arginine and protein metabolism were studied using organ-balance, stable-isotope techniques. Systemic NO production was increased in the endotoxin-treated mice. In addition, renal protein synthesis and de novo arginine production from citrulline were increased. However, no effect on renal NO production was observed. In conclusion, increased renal de novo arginine production may serve to sustain systemic NO production. To our knowledge, it was shown for the first time that renal protein synthesis is enhanced in the early response to endotoxemia.

Amino Acids↗

PubMed1977

Renal response to vasopressin after inhibition of prostaglandin synthesis.

The renal effects of vasopressin (VP) in water-loaded and hydropenic conscious dogs were examined with and without the previous administration of prostaglandin (PG) synthesis inhibitors (indomethacin and meclophenamate). The parameters studied were: urinary output, sodium and potassium excretion, plasma and urinary osmotic concentration, total renal blood flow, mean arterial pressure, heart rate, and the clearance and extraction ratio of p-aminohippuric acid and inulin. The infusion of VP caused antidiuresis and marked saluresis during water diuresis, whereas it was found to be diuretic and saluretic in hydropenic animals. Inhibition of PG synthesis greatly enhanced the antidiuretic activity of VP and abolished its saluretic and diuretic actions. Changes in renal water and solute excretion and changes in the hemodynamic parameters are uncorrelated. It is concluded that intrarenal PGs may play an important role in modulating the renal action of VP.

Animals↗

PubMed1983

Sulfate transport by flounder renal tubule brush border: presence of anion exchange.

Transport of sulfate into brush border membrane (BBM) vesicles from renal tubules of southern flounder, Paralichthys lethostigma, was investigated. Imposition of a 21 mM HCO-3 gradient, in greater than out, produced concentrative sulfate uptake (overshoot) fourfold higher than equilibrium. Gradient conditions were necessary to produce this response; no overshoot was produced by the mere presence of HCO-3. Generation of potassium diffusion potentials with KCl gradients and valinomycin or short-circuiting of possible other ionic diffusion potentials had no effect on sulfate uptake. The rate-limiting step in HCO-3:SO2-4 exchange is, therefore, an electroneutral process. Although HCO-3 was the most effective counterion for sulfate, SCN-, Cl-, and S2O2-3 were also capable of promoting concentrative sulfate uptake. Sulfate uptake in the absence of counterion and bicarbonate-dependent sulfate uptake were both shown to be saturable processes. HCO-3-driven sulfate uptake could be inhibited by disulfonic stilbene, HgCl2, probenecid, chlorophenol red, and bromcresol green. Phloridzin, p-aminohippuric acid, 2,4-dinitrophenol, isethionic acid, and citric acid had no significant effect on HCO-3:SO2-4 exchange. The role of this sulfate:anion exchanger in active renal tubule sulfate secretion is discussed.

Adenosine Triphosphatases↗

PubMed1985

Transport of N1-methylnicotinamide across brush border membrane vesicles from rabbit kidney.

A preparation of isolated brush border membranes from the rabbit renal cortex was used to examine the characteristics of N1-methylnicotinamide (NMN) transport in the kidney. Transport was independent of the presence of Na+ under Na+ equilibrium conditions. However, outwardly directed Na+ gradients stimulated NMN uptake, whereas inwardly directed Na+ gradients inhibited NMN uptake. Transport appeared to involve two parallel processes: one saturable with a Jmax of 5 nmol X mg protein-1 X min-1 and an apparent Kt of 0.6 mM, and a second that behaved like passive diffusion. Countertransport of NMN was observed when vesicles were preloaded with either NMN or another organic cation, tetraethylammonium (TEA). TEA and several structural analogues, as well as a wide variety of other organic cations and bases, were effective inhibitors of NMN uptake, though nicotinamide and p-aminohippuric acid did not interact with the uptake process. Outwardly directed proton gradients (pH 6.0 in, 7.6 out) stimulated transport, suggesting that NMN uptake may involve a countertransport of H+. The electrical potential difference across the vesicle membrane was manipulated using gradients of the permeant organic ion thiocyanate (SCN-); an outwardly directed gradient of SCN- (i.e., a depolarizing condition) stimulated uptake and produced a transient accumulation of NMN above that noted at equilibrium, whereas an inwardly directed SCN- gradient inhibited uptake of NMN. The data can be explained by postulating the presence of an electrogenic NMN+-H+ antiporter in the rabbit luminal membrane that could play a role in organic cation secretion.

Animals↗

PubMed1986

Primary culture of flounder renal tubule cells: transepithelial transport.

Renal proximal tubule cells from the winter flounder (Pseudopleuronectes americanus) were maintained in a functionally differentiated state for up to 16 days in primary culture on floating collagen gels. The cells were confluent after 7-8 days in culture, contracted the collagen gels, and exhibited ciliary activity. Electron microscopy indicated that the cultures were composed of continuous sheets of columnar epithelial cells that had established structural polarity. When mounted in Ussing chambers, the cultures exhibited a small mucosa-negative potential difference (0.6 +/- 0.10 mV) and a low transepithelial resistance (23 +/- 2.3 omega X cm2). Short-circuit current averaged 24 microA/cm2. The cultured epithelium was four times more permeable to Na than to Cl and actively secreted sulfate and p-aminohippuric acid and reabsorbed hexoses. Glucose reabsorption was rheogenic and occurred via a high-affinity (Km = 0.16 mM), low-capacity (Vmax = 5 microA/cm2), phlorizin-sensitive transport system. We concluded that the cultured cells express many of the differentiated properties of the intact flounder proximal tubule and thus provide a suitable model system for studying renal transport processes.

Acids↗

PubMed1987

Transport of tetraethylammonium by rabbit renal brush-border and basolateral membrane vesicles.

Brush-border and basolateral membrane vesicles (BBMV and BLMV, respectively) from rabbit renal cortex were used to study transport of the organic cation, tetraethylammonium (TEA). Outwardly directed proton gradients stimulated uptake of TEA into BBMV and supported concentrative accumulation. Furthermore, an inwardly directed H+ gradient accelerated TEA efflux from BBMV. These data suggest that TEA transport in BBMV involved exchange with H+. The Jmax and Kt for TEA transport into BBMV under pH equilibrium conditions (pH 7.5) were 2.1 nmol.mg-1.min-1 and 0.15 mM, respectively. Under pH gradient conditions (6.0in:7.5out), Jmax increased by 270% with no effect on Kt. Uptake of TEA into BBMV was stimulated by an inside-positive electrical potential difference (PD), although exchange of TEA for H+ appeared to be one for one. In BLMV, H+ gradients had little effect on TEA uptake and were incapable of supporting concentrative transport. The Jmax and Kt for TEA transport in BLMV were 0.33 nmol.mg-1.min-1 and 0.37 mM, respectively. Inside-negative PDs stimulated this uptake, suggesting that it involved an electrically conductive pathway. TEA transport in BBMV and BLMV was inhibited by amiloride and cimetidine, although p-aminohippuric acid was without effect. Thus, secretion of TEA involves carrier-mediated transport steps at both the luminal and peritubular membranes, although an active step is not evident in isolated BLMV.

Animals↗

PubMed1988

Transport of tetraethylammonium by a kidney epithelial cell line (LLC-PK1).

We investigated whether the LLC-PK1 epithelial cell line (which shows many characteristics of proximal tubular cells) also is capable of transporting an organic ion. Suspended LLC-PK1 cells accumulated tetraethylammonium (TEA). The uptake showed characteristics of a facilitated mechanism; TEA uptake was saturable and temperature-dependent and was inhibited by other organic cations. Quinine and mepiperphenidol were the most potent inhibitors, whereas N1-methylnicotinamide and morphine inhibited the transport system only slightly at doses of 10(-3) M. Basolateral-to-apical TEA flux through LLC-PK1 monolayers was five to six times larger than that of mannitol, a nontransported compound, whereas apical-to-basolateral TEA and mannitol fluxes were equal. Only the basolateral-to-apical TEA flux was inhibited by quinine. Under similar experimental conditions, no transport of p-aminohippuric acid was observed. It is concluded that LLC-PK1 cells are able to transport TEA, as do cells of the proximal tubule.

Animals↗

PubMed1988

Microsomal protein synthesis inhibition: an early manifestation of gentamicin nephrotoxicity.

Aminoglycoside antibiotics achieve bacterial killing by binding to bacterial ribosomes and inhibiting protein synthesis. To examine whether similar mechanisms could be present in renal tubular cells prior to the onset of overt proximal tubular necrosis due to these drugs, we isolated microsomes from Fischer rats given 20 mg/kg gentamicin every 12 h subcutaneously for 2 days and from vehicle-injected controls. Concomitant studies of renal structure, function, and mitochondrial respiration were carried out. [3H]leucine incorporation into renal microsomes of treated animals was reduced by 21.9% (P less than 0.01), whereas brain and liver microsomes from the same animals were unaffected. Gentamicin concentration in the renal microsomal preparation was 56 micrograms/ml, a value 7- to 10-fold above concentrations necessary to inhibit bacterial growth. Conventional renal function studies were normal (blood urea, serum creatinine, creatinine clearance). Treated animals showed only a mild reduction of inulin clearance, 0.71 compared with 0.93 ml.min-1.100 g-1 in controls (P less than 0.05), and an increase in urinary excretion of N-acetylglucosaminidase of 20 compared with 14.8 units/l (P less than 0.05). Renal slice transport of p-aminohippuric acid, tetraethylammonium, and the fractional excretion of sodium were well preserved. There was no evidence, as seen by light microscopy, of proximal tubular necrosis. Mitochondrial cytochrome concentrations were normal and respiratory activities only slightly reduced. Processes similar to those responsible for bacterial killing could be involved in experimental gentamicin nephrotoxicity before overt cellular necrosis.

Animals↗

PubMed1988

Effects of intrarenal adenosine on renal function and medullary blood flow in the rat.

Adenosine is a potent vasodilator of the systemic circulation. Infusion of adenosine into the aorta causes water and sodium retention and a fall in glomerular filtration rate and renal blood flow. The effect of adenosine on medullary blood flow is unknown. Because systemic vasodilatory effects may confound its renal actions, adenosine was infused into the renal artery of anesthetized Munich-Wistar rats at doses of 2, 6, and 15 micrograms/min. A marked dose-dependent increase in urinary flow and sodium excretion was observed. Inulin and p-aminohippuric acid clearance did not change significantly. Blood flow in vasa recta in the exposed renal papilla, as determined by fluorescence videomicroscopy, increased significantly only with the highest dose of adenosine. In control animals infused with the vehicle only, there was no change in any of the above variables. These results indicate that direct intrarenal infusion of adenosine in the rat increases urinary flow and sodium excretion and at higher doses also increases vasa recta blood flow. The effects on urinary flow and sodium excretion were therefore mediated by a mechanism other than an increase in vasa recta blood flow.

Adenosine↗

PubMed1989

Response to atrial natriuretic peptide in dogs with hypovolemic acute pancreatitis.

The ability of atrial natriuretic peptide (ANP) to preserve renal function in dogs with hypovolemic acute renal insufficiency was tested in anesthetized dogs 4 h after the induction of acute pancreatitis. Plasma volume had decreased by 21.5% and glomerular filtration rate (GFR) by 43.2%. Blood pressure had declined by 30 mmHg. ANP was given intravenously at 50 and 150 ng.kg-1.min-1. With the lower dose, blood pressure (BP), GFR, and clearance of p-aminohippuric acid (CPAH) did not change but urine flow (V) and sodium excretion (UNaV) increased. With the higher dose, BP declined by 25 mmHg, GFR declined, but V and UNaV still increased. When plasma volume was maintained with 4% colloid during the progression of pancreatitis and ANP 50 ng.kg-1.min-1 given, BP declined, GFR did not change, and there was a magnified increment in V and UNaV. The administration of glucagon (5 micrograms/min iv) to dogs with hypovolemic pancreatitis caused BP to decline by 17 mmHg. Despite a major increment in GFR, fractional excretion of sodium increased only slightly, compared with that obtained with ANP. We conclude that glucagon preserves GFR more effectively than ANP in hypovolemia, but ANP is more effective in protecting urinary water and sodium excretion.

Acute Disease↗

PubMed1990

Direct effects of endothelin in the rat kidney.

In the present study, we tested the direct effects of endothelin (ET) on rat kidney in vivo. ET was infused into the left renal artery of anesthetized rats at a rate of 0.5, 5, 20, or 40 pmol/h. ET reduced ipsilateral urine volume (V), clearance of inulin (CIN), and clearance of p-aminohippuric acid (CPAH) in a dose-dependent manner. Thus ET at 20 pmol/h did not change V but decreased renal plasma flow (RPF) and glomerular filtration rate (GFR) by 27.6 +/- 14.3 and 30.8 +/- 10.4%, respectively, in the ipsilateral kidney. ET at 0.5 pmol/h was without effect and at 5 pmol/h had only minor effects on CIN and CPAH of ipsilateral kidney. At 40 pmol/h, ET reduced ipsilateral V, GFR, and RPF by 52.3 +/- 21.4, 58.4 +/- 14.5, and 72.5 +/- 10.6%, respectively. Filtration fraction and fractional excretion of Na remained unchanged during ET infusion. ET, 40 pmol/h, infused into the renal artery together with atrial natriuretic peptide (ANP) at a rate of 12 pmol/h reduced the ipsilateral V, GFR, and RPF by 33.2 +/- 6.3, 26.1 +/- 6.0, and 27.2 +/- 7.1%, respectively, decrements less than those with ET alone. When a calcium-channel blocker nicardipine was infused at a rate of 2.5 micrograms/h into the renal artery together with ET, 20 pmol/h, there was little change in the ipsilateral V, RPF, and GFR; ET, 40 pmol/h, with nicardipine did not change V and decreased GFR and RPF by 25.9 +/- 5.6 and 23.1 +/- 10.8%, respectively, decrements less than those without nicardipine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Organic cation transport in human renal brush-border membrane vesicles.

The renal proximal tubule is responsible for the active elimination of organic cations. Studies in brush-border membrane vesicles (BBMV) suggest that active organic cation transport is mediated by an organic cation-proton antiporter. The goals of this study were to determine whether this transporter is expressed in human kidney and to elucidate its characteristics. Transport of the organic cations N1-[3H]methylnicotinamide (NMN) and [14C]tetraethylammonium (TEA) was determined by rapid filtration in BBMV of donor human kidneys. The uptake of NMN and TEA was driven against a concentration gradient by an outwardly directed proton gradient. NMN uptake was inhibited by the organic cations TEA, NMN, quinine, and cimetidine, but was not affected by p-aminohippuric acid, cephalexin, and polyamines. The electroneutral transport of NMN was characterized by a Km of 0.44 +/- 0.07 mM and a Vmax of 24.4 +/- 15.2 pmol.mg protein-1.s-1. The rate of proton efflux from BBMV increased in the presence of an inwardly directed TEA gradient. Preloading BBMV with NMN or TEA trans-stimulated the initial rate of uptake of TEA. Therefore the human proximal tubule expresses an organic cation-proton antiporter in the brush-border membrane. The antiporter is similar to that described in other mammalian species but shows some differences in its transport characteristics.

Adult↗

PubMed2005

Kinetics of glucose transport and sequestration in lactating bovine mammary glands measured in vivo with a paired indicator/nutrient dilution technique.

To quantify kinetics of mammary glucose utilization in vivo, 24 paired glucose and extracellular indicator (p-aminohippuric acid) dilution curves across intact bovine mammary glands were obtained after bolus injections into the external iliac artery. Dilution curves were analyzed using a compartmental capillary, convolution integration model. Four candidate submodels of glucose transport and metabolism in capillary supply zones were fit to the glucose dilution curves and evaluated. Model I, with one extracellular compartment for glucose and first-order unidirectional uptake, failed, indicating that efflux of glucose from the intracellular space could not be ignored. Model II, with first-order exchanges between extracellular and intracellular compartments and sequestration from the latter, was overdefined because unidirectional clearance of glucose was at least five times the blood flow rate and 20 times the net clearance rate. Model III, combining extracellular and intracellular space into one compartment, was superior in its goodness-of-fit to curves and identifiability of parameters. Michaelis-Menten parameters of sequestration were not identifiable. Parameters of the optimal compartmental capillary, convolution integration model were applicable to both the dynamics of injected glucose dilution and the steady-state background arteriovenous difference of glucose. Glucose sequestration followed first-order kinetics between 0 and 7 mM extracellular glucose with an average rate constant of 0.006 s(-1) or a clearance of 44 ml/s. The ratio of intracellular to extracellular glucose distribution space was 0.34, which is considerably lower than the expected intracellular volume and suggests an intracellular occlusion compartment with which extracellular glucose rapidly exchanges.

Animals↗

PubMed1980

Kidney storage at subzero temperatures using a hyperosmolar perfusate.

32 dog kidneys were stored in a hyperosmolar perfusate (770 mosm/kg) at minus2 and plus4 degrees C, respectively, for 12-48 h and thereafter autotransplanted. 18 kidneys of the control group were stored in Collins solution at plus4 degrees C. The immediate function of the kidneys after transplantation was measured by p-aminohippuric acid and inulin clearances. Successful 24-hour preservation was possible by use of the hyperosmolar perfusate. Kidneys stored in the hyperosmolar perfusate at minus2 degrees C were better preserved than kidneys stored in Collins solution at plus4 degrees C. The addition of human albumin to the hyperosmolar perfusate did not improve the preservation results.

Albumins↗