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PubMed1988

Hemoglobin- and myoglobin-induced acute renal failure in rats: role of iron in nephrotoxicity.

In ischemic acute renal failure oxygen free radicals may mediate injury. In addition, iron appears to play a critical role in hydroxyl radical formation and lipid peroxidation during reperfusion of ischemic kidneys. To determine whether iron may play a similar role in pigment (heme protein)-induced acute renal failure, we studied the effects of the iron chelator deferoxamine in two experimental models of pigment-induced acute renal failure, intramuscular glycerol injection and intravenous hemoglobin infusion without and with concurrent ischemia in the rat. Intramuscular injection of 50% glycerol (5 ml/kg) caused inulin clearance to fall to 0.13 +/- 0.03 (SE) ml/min (normal value, 1.0-1.2 ml/min). Continuous infusion of deferoxamine beginning at the time of glycerol injection significantly attenuated this renal dysfunction. Deferoxamine-treated animals had an inulin clearance of 0.37 +/- 0.06 ml/min (P less than 0.01). Glycerol injection was also associated with significant lipid peroxidation, measured as renal malondialdehyde content. Deferoxamine-treated glycerol-injected rats had renal malondialdehyde content not significantly different from control animals. In another model of heme pigment-induced renal injury, hemoglobin was infused to produce hemoglobinuria. Inulin clearance 1 h after hemoglobin infusion was significantly reduced to 0.84 +/- 0.5 ml/min (P less than 0.025). Infusion of deferoxamine after hemoglobin prevented the hemoglobin-induced decrease in inulin clearance. Thirty minutes of renal ischemia followed by infusion of hemoglobin resulted in more severe renal dysfunction with inulin clearance of 0.54 +/- 0.08 ml/min. Deferoxamine infused at the time of reperfusion attenuated the fall in glomerular filtration rate after ischemia and hemoglobin infusion:inulin clearance 1.04 +/- 0.07 (P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Kidney Injury↗
PubMed1985

Volume regulation and plasma membrane injury in aerobic, anaerobic, and ischemic myocardium in vitro. Effects of osmotic cell swelling on plasma membrane integrity.

The relationship between cell swelling and plasma membrane disruption has been evaluated in thin myocardial slices incubated in oxygenated or anoxic Krebs-Ringer phosphate media. Electron microscopy and measurements of inulin-diffusible space were used to monitor plasma membrane integrity. Inulin is excluded from the intracellular space of intact cells; therefore, an increase in tissue inulin content is an excellent marker of loss of plasma membrane integrity. Cell volume was increased during exposure of aerobic slices to hypotonic media, but the inulin-diffusible space was not increased and electron micrographs showed no detectable plasma membrane alterations. Likewise, during prolonged anoxic isotonic incubation, no evidence of plasma membrane damage was observed. Incubation in anoxic hypotonic media for 60 minutes resulted in a larger increase in cell volume than under aerobic conditions, but plasma membrane integrity was maintained. Extended anoxic hypotonic incubation (300 minutes) produced no further change in tissue water, but the inulin-diffusible space was increased and electron micrographs revealed breaks in the plasma membranes primarily in association with large subsarcolemmal blebs. Likewise, myocardial slices incubated in isotonic anoxic media for 240 minutes and hypotonic anoxic media for 60 minutes had an increased inulin-diffusible space and the ultrastructural appearance was similar. This ultrastructural appearance is indistinguishable from that observed in myocytes lethally injured by ischemia. Measurements of tissue osmolarity during total ischemia showed that osmotically induced cell swelling could occur in ischemic myocardium prior to the onset of plasma membrane disruption. Our results indicate that cell swelling per se is incapable of rupturing plasma membranes; however, after prolonged periods of energy deficiency, the plasma membrane or its cytoskeletal scaffold become injured, which allows the membrane to rupture if the cell is swollen, as might occur during ischemia or reperfusion.

Aerobiosis↗
PubMed1998

Relative accuracy of renal scan in estimation of renal function during partial ureteral obstruction.

This study is designed to evaluate the relative ability of DMSA and DTPA renal scans to accurately reflect differential renal function (DRF) compared with inulin clearance in the presence of partial unilateral ureteral obstruction. DRF was determined in 29 young rabbits by both renal scans. In the experimental group (n=21), left partial ureteral obstruction was created. Following 8 to 24 weeks, individual renal function in the obstructed animals were assessed by both renal scans and clearance of inulin. Eight animals were used as control. In the control group, DRF measured by DMSA, but not DTPA, correlated well with inulin clearance. Both scans documented a significant change in the DRF of the obstructed group (p<0.001). In the partially obstructed kidneys DRF derived by inulin was significantly lower than that measured by DMSA or DTPA scans (p<0.001 and p<0.0001). DRF measured by DMSA correlates well with inulin clearance in the control group. A similar correlation was not obtained by DMSA in the presence of obstruction. DTPA does not correlate with inulin clearance either in the control or the obstructed group.

Journal Article↗
PubMed1989

The effects of mannitol diuresis on digoxin and phenobarbital handling by the kidney: implications for tubular reabsorption and secretion of the cardiac glycoside.

The effect of mannitol diuresis on the renal clearance of digoxin and phenobarbital was studied in dogs. Mannitol diuresis significantly increased the clearance of digoxin and the ratio digoxin: inulin clearances (from 0.7 +/- 0.2 to 1.1 +/- 0.25). The increase in phenobarbital: inulin clearance ratio was significantly higher than the increase in the digoxin: inulin clearance ratio (4.9 fold vs 1.66 fold) (p less than 0.005). Mannitol diuresis did not significantly affect inulin clearance, nor digoxin protein binding during the experimental period while there was a significant increase in PAH clearance. Significant correlations were found between urine flow rate and digoxin renal clearance or digoxin: inulin clearance ratio. The increase in the ratio drug: inulin clearance with diuresis correlated inversely with the initial ratio; animals with more predominant net reabsorption had a higher increase in ratio. These studies suggest that the mannitol-induced increase in digoxin clearance stems from a combination of increased renal blood flow enhancing digoxin secretion, and increased urine flow rate inhibiting its reabsorption. We conclude that urine flow rate and renal blood flow are important determinants of the renal clearance of digoxin, independent of GFR. Any study assessing the effect of pathophysiological states or drug interactions on digoxin renal clearance must control for these factors.

Animals↗
PubMed1990

Adenylate cyclase and protein kinase C mediate opposite actions on endothelial junctions.

To determine whether the endothelial paracellular pathway is regulated, the effect of intracellular messengers on the transendothelial flux of inert radiolabeled molecules of diverse molecular size was examined in bovine aortic endothelial cells grown on collagen-coated filters. The endothelial monolayers showed a modest electrical resistance (21 +/- 10 delta.cm2; m +/- SD) and restricted the passage to 14C-sucrose, 3H-inulin, 14C-dextran (70 kDa), and 125I-polyvinyl pyrrolidone (125I-PVP, 360 kDa) according to their molecular mass. 8-Bromoadenosine 3'-5' cyclic monophosphate (8-Br-cAMP) reduced by more than 30% the permeability coefficients of 14C-sucrose and 3H-inulin but had no effect on the permeability of 125I-PVP. The permeabilities of 14C-sucrose and of 14C-inulin were strikingly increased by activating protein kinase C (PKC) by phorbol 12-myristate-13-acetate or sn-1,2-dioctanoly-glycerol whereas the latter compound had no effect on the permeability of 125I-PVP. In addition, the permeability of 14C-sucrose was unchanged by a phorbol ester that does not activate PKC. Increasing intracellular calcium with ionomycin had no effect on the permeability of 14C-sucrose. None of these maneuvers significantly affected the protein content of the endothelial monolayers. The results indicate that 8-Br-cAMP and PKC activators modulate a pathway across the endothelial monolayer that excludes 125I-PVP (360 kDa) but readily accepts 14C-sucrose and 3H-inulin, suggesting that this pathway is the paracellular pathway. Hence, low molecular weight molecules such as sucrose and inulin can be used to probe the behavior of the paracellular pathway of endothelial monolayers grown in vitro. The results also indicate that the paracellular pathway in endothelium is regulated and suggest that endothelial junctions can be closed by simulating adenylate cyclase and opened by stimulating protein kinase C.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1997

Intracellular, interstitial and plasma spaces in the rat myocardium in vivo.

The aim of this study was to determine tissue water spaces in rat heart in vivo using [14C]-inulin or D-[14C]-mannitol as extracellular markers, and 2,3DPG as whole blood tissue marker. Tracer was injected into the jugular vein of anaesthetised male Sprague-Dawley rats (60 mg/kg) and allowed to equilibrate for 30 min. A blood sample was then taken and the heart was freeze-clamped at liquid N2 temperatures within 5 s of opening the chest cavity. Extracellular space was calculated by dividing the total tissue counts (d/min/g) by plasma counts (d/min/g). The extracellular inulin and mannitol spaces were 0.212+/-0.010 and 0.236+/-0.012 ml/g wet weight tissue, respectively (n=5). Expressed as a percentage of total tissue water (0.79+/-0.012 ml/g wet weight tissue, n=9), the intracellular space was found to be 73.1 (inulin) and 70.1% (mannitol). The interstitial space was calculated by subtracting the counts in tissue due to whole blood from total tissue counts and dividing by plasma counts. The interstitial space was 19.4 and 21. 9%; and the plasma space was 7.5 and 8.0% for the inulin and mannitol methods, respectively. We conclude that (i) there was no significant differences in the inulin or mannitol spaces in the in vivo heart (P<0.05), demonstrating that either marker provides a reliable and quantitative estimate of extracellular space, and (ii) 2,3-DPG can be used as a reliable indicator of tissue whole blood which can then be used in combination with the tracer method to calculate the interstitial and plasma spaces.

2,3-Diphosphoglycerate↗
PubMed1994

Cationic amino acid fluxes beyond the proximal convoluted tubule of rat kidney.

To investigate the fluxes of cationic amino acids beyond the proximal convolution, we micropunctured and microperfused superficial tubules of male Wistar rats in vivo et situ. In free-flow micropuncture experiments, the concentrations of endogenous L-arginine+, [Arg], and of intravenously infused L-homoarginine+, [HoArg], were determined by HPLC. Fluorescein isothiocyanate-labeled inulin was detected on-line in the same tubular fluid samples. To determine undirectional fluxes, radiolabeled Arg and inulin were (1) microperfused through short loops of Henle and (2) microinfused into different tubule segments to measure urinary recovery of the radiolabel. At a mean [Arg]plasma of 116 mumol/l, [Arg] was 9.3 mumol/l in the late proximal tubule (LPT), and 35.6 mumol/l in the early distal tubule (EDT) corresponding to fractional deliveries (FD) of 0.055 in LPT and 0.078 in EDT. Fractional urinary excretion (FE) of Arg was 0.00033 (P < 0.05 vs FDEDT). Infusion of HoArg (2.5 or 7.5 mumol/min) led to respective mean [HoArg]plasma values of 1.44 and 3.73 mmol/l, and resulted in respective FDLPT values for HoArg of 0.23 and 0.53, respective FDEDT values of 0.29 and 0.41, and finally, respective FE values for HoArg of 0.25 and 0.58. When short loops of Henle were microperfused with 1 or 50 mmol/l [14C]Arg (+[3H]inulin), fractional recovery (FR) of 14C (relative to inulin) in the EDT was 0.13 and 0.36, respectively. During microinfusion of radiolabeled Arg (1 or 50 mmol/l) and inulin into LPT, the urinary FR of the radiolabel was 0.14, or 0.59, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids, Diamino↗
PubMed1977

The early phase of experimental acute renal failure. II. tubular leakage and the reliability of glomerular markers.

Experiments were designed to determine whether leakage of substances across the tubular epithelium, which are impermeant in the normal kidney, falsifies the measurement of glomerular filtration rate in acute renal failure. Permeability to those substances most commonly used for filtration rate determination, polyfructosan, inulin and ferrocyanide, was estimated by measuring their recoveries following perfusion through various nephron segments in haeme pigment, ischaemic and nephrotoxic models of acute renal failure. Late proximal recovery of 14C ferrocyanide was only marginally decreased compared to controls, by a maximum of 6%. Distal recovery of polyfructosan, 14C and 3H inulin were depressed somewhat more, by a maximum of 11%. Urinary recovery of 14C inulin was reduced by only 15% in kidneys showing severely restricted renal function. It is concluded that tubular leakage is not a feature of significance in the early phase of moderate acute renal failure, that ferrocyanide and inulin are reliable markers for the determination of nephron filtration rate and water reabsorption, and that the reduction in whole kidney inulin or polyfructosan clearance reflects primarily a reduction in glomerular filtration rate.

Acute Kidney Injury↗
PubMed1982

Glomerular and tubular function in non-oliguric acute renal failure.

Glomerular and tubular function were evaluated in 30 non-oliguric patients with increasing azotemia following open heart surgery. Fractional clearances (theta) of test solutes relative to that of inulin were determined. In 16 patients, theta dextran (radius 22 to 30 A) exceeded unity, a finding attributed to inulin backleak through necrotic tubules. These patients were classified as having acute renal failure; 14 subsequently required dialysis. In the remaining patients (N = 14), theta dextran was normal. These patients were considered to have prerenal failure; all recovered spontaneously. clearance of inulin (Cin) was lower in acute renal failure than in prerenal failure (12 +/- 2 versus 18 +/- 2 ml/min/1.73 m2; p less than 0.025). The apparent difference in glomerular filtration rate when Cin is used as an index was abolished, however, when Cin in acute renal failure was corrected for tubule backleak of inulin. In acute renal failure, fractional clearance of p-aminohippurate (theta PAH) was 7.1 +/- 1.0, and fractional excretion of potassium (FEk) was 160 +/- 18 percent. These findings strongly suggest that secretory ability in both proximal and terminal tubule augments, respectively, is preserved in acute renal failure. Compared with prerenal failure, the urine-to-plasma inulin ratio was lower (U/Pin = 10 +/- 1 versus 25 +/- 4; p less than 0.005) and FENa was higher (FENa = 5.1 +/- 1.5 versus 0.5 +/- 1.0 percent; p less than 0.01) in acute renal failure.

Acute Kidney Injury↗
PubMed1976

Renal clearances of estriol conjugates in normal human pregnancy at term.

In late human pregnancy more than 90 per cent of the total estriol (E3) in body fluids consists of four conjugates, estriol-3-sulfate (E3-3S), estriol-16-glucosiduronate (E3-16G), estriol-3-glucuronide (E3-3G), and estriol-3-sulfate-16-glucosiduronate (E3-3S-16G). Since the relative amounts of E3 in blood and urine would be determined by the kidney, the renal clearance of each conjugate was determined and compared with inulin and p-aminohippuric acid (PAH) clearance, as measures of glomerular filtration rate (GFR) and the effective renal plasma flow. Five women were studied in the lateral decubitus position with inulin and PAH infusion. Samples of blood and urine were collected at 40 minute intervals and analyzed. The method for E3 conjugates involved separation of the four conjugates on Sephadex LH-20, enzyme hydrolysis, and radioimmunoassay. Renal clearances for E3-3S and E3-3S-16G were below inulin. E3-3G approximated inulin; E3-16G exceeded inulin and approached PAH. In plasma E3-3S-16G represented 48.4 +/- 7.2 per cent; in urine E3-16G represented 69.5 +/- 7.3 per cent of total E3. Thus, different conjugates predominate in blood and urine.

Aminohippuric Acids↗
PubMed1985

Right and left cortical lesions asymmetrically alter cerebrovascular permeability in the rat.

Vascular permeability and intravascular space in the rat cerebral cortex and hypothalamus were assessed 5 and 14 days after the production of either right or left hemisphere frontal cortical suction lesions. Rats were intravenously injected with large (dextran, 50,000 kdalton) and small (inulin, 5000 kdalton) molecular tracers and tissue samples were removed for assay after 7 min. Five days following lesions of the right but not left hemisphere, inulin levels in the cortical region posterior and contralateral to the lesion site were significantly higher than control values. Dextran levels were not increased in this region by lesions of either hemisphere. However, both right and left hemisphere lesions led to a significant elevation of inulin and dextran levels (inulin higher than dextran) in the cortex surrounding the lesion site. Fourteen days after lesion of either hemisphere, tracer levels were not elevated over control in any region examined. These results suggest that both right and left hemisphere cortical lesions transiently increase local vasopermeability (and perhaps intravascular space), but that only right hemisphere lesions selectively increase inulin in cortex distant from the lesion site, probably from lesion-induced alterations in cerebrovascular permeability.

Animals↗
PubMed2006

Characterization of the molecular distribution of drugs in glassy solid dispersions at the nano-meter scale, using differential scanning calorimetry and gravimetric water vapour sorption techniques.

The molecular distribution in fully amorphous solid dispersions consisting of poly(vinylpyrrolidone) (PVP)-diazepam and inulin-diazepam was studied. One glass transition temperature (T(g)), as determined by temperature modulated differential scanning calorimetry (TMDSC), was observed in PVP-diazepam solid dispersions prepared by fusion for all drug loads tested (10-80 wt.%). The T(g) of these solid dispersions gradually changed with composition and decreased from 177 degrees C for pure PVP to 46 degrees C for diazepam. These observations indicate that diazepam was dispersed in PVP on a molecular level. However, in PVP-diazepam solid dispersions prepared by freeze drying, two T(g)'s were observed for drug loads above 35 wt.% indicating phase separation. One T(g) indicated the presence of amorphous diazepam clusters, the other T(g) was attributed to a PVP-rich phase in which diazepam was dispersed on a molecular level. With both the value of the latter T(g) and the DeltaC(p) of the diazepam glass transition the concentrations of molecular dispersed diazepam could be calculated (27-35 wt.%). Both methods gave similar results. Water vapour sorption (DVS) experiments revealed that the PVP-matrix was hydrophobised by the incorporated diazepam. TMDSC and DVS results were used to estimate the size of diazepam clusters in freeze dried PVP-diazepam solid dispersions, which appeared to be in the nano-meter range. The inulin-diazepam solid dispersions prepared by spray freeze drying showed one T(g) for drug loads up to 35 wt.% indicating homogeneous distribution on a molecular level. However, this T(g) was independent of the drug load, which is unexpected because diazepam has a lower T(g) than inulin (46 and 155 degrees C, respectively). For higher drug loads, a T(g) of diazepam as well as a T(g) of the inulin-rich phase was observed, indicating the formation of amorphous diazepam clusters. From the DeltaC(p) of the diazepam glass transition the amount of molecularly dispersed diazepam was calculated (12-27 wt.%). In contrast to the PVP-diazepam solid dispersions, DVS-experiments revealed that inulin was not hydrophobised by diazepam. Consequently, the size of diazepam clusters could not be estimated. It was concluded that TMDSC enables characterization and quantification of the molecular distribution in amorphous solid dispersions. When the hygroscopicity of the carrier is reduced by the drug, DVS in combination with TMDSC can be used to estimate the size of amorphous drug clusters.

Adsorption↗
PubMed1986

Limitations of creatinine in quantifying the severity of cyclosporine-induced chronic nephropathy.

The glomerular filtration rate (GFR), as measured by the clearance of inulin, was depressed severely in 34 heart transplant recipients receiving cyclosporine (CsA) for 12 months or longer. The clearance of 99mTc-DTPA, a filtration marker similar in size to creatinine, was identical to that of the larger inulin molecule. In contrast, the clearance of creatinine was enhanced (P less than .01) such that its fractional clearance (relative to inulin) averaged 1.51 +/- 0.05. Moreover, there was an inverse relationship between fractional creatinine clearance (r = 0.36, P less than .01) and absolute inulin clearance. We conclude that in CsA-induced chronic nephropathy 99mDTPA and inulin are unrestricted by the glomerular capillary wall and behave as true filtration markers, creatinine is progressively hypersecreted by renal tubules as the nephropathy worsens, and the ensuing enhancement of creatinine clearance over GFR blunts the expected rise in serum creatinine levels as GFR falls. As a result, serum creatinine in chronic CsA-induced glomerulopathy exceeds 2 mg/dL consistently, only after true GFR has become depressed below normal values by two thirds or more.

Adult↗
PubMed2000

Prediction of in vivo tissue distribution from in vitro data 1. Experiments with markers of aqueous spaces.

PURPOSE: The aim of this study was to evaluate the ability of an in vitro method of tissue distribution to accurately predict total water and extracellular aqueous spaces using marker compounds urea and inulin. METHODS: Slices (50-200 mg) of all the major tissues in the rat were incubated with Hanks/HEPES pH7.4 buffer containing 14C-urea and 3H-inulin for 2 h at 37 degrees C. Tissue weight was noted before and after incubation and the tissue-to-buffer ratios determined. RESULTS: 14C-Urea Kp estimates were generally greater than total tissue water due to tissue swelling, which varied widely among the tissues, up to 41% in muscle. In most cases, Kp values were much closer to in vivo values after correcting for the 14C-urea in the imbibed media (Kpcorr). The method was able to distinguish between 14C-urea and 3H-inulin Kp values and indicated that inulin occupied a smaller space than urea, which for the majority of tissues corresponded to the extracellular space. CONCLUSIONS: The Kp(corr) values for 14C-urea and Kp for 3H-inulin were consistent with total tissue water and extracellular space for the majority of tissues studied, indicating their suitability as marker compounds for checking the viability of this in vitro method for estimating tissue distribution.

Animals↗
PubMed1991

Evaluation of "true" creatinine clearance in rats reveals extensive renal secretion.

The renal clearance of endogenous creatinine is widely used to assess glomerular filtration rate (GFR) and renal function in animal investigations. The objective of the present investigation was to evaluate the extent of renal secretion of endogenous creatinine in rats and the effect of probenecid, the classical inhibitor of organic anion transport, on creatinine clearance. Ten female Lewis rats received 3H-inulin (5-muCi i.v. bolus followed by 5 muCi/hr) throughout a 6-hr period. Three hours after initiation of the inulin infusion, probenecid was administered (92.4-mg/kg i.v. bolus followed by 0.59 mg/min/kg). Steady-state serum concentrations of about 500 micrograms/ml probenecid were achieved. Renal clearance was assessed between 1 and 3 hr (control) and between 4 and 6 hr (probenecid treatment). A preliminary study in seven rats demonstrated no time-dependent change in inulin or creatinine clearance between these two study intervals. Creatinine clearances were determined by an alkaline picrate assay which incorporated Fuller's earth (Lloyd reagent) to remove interfering noncreatinine chromogens from serum samples and these values were compared with those using a nonspecific picrate assay. "True" clearance ratios of creatinine to inulin (Clcr/CLin) were greater than unity (2.33 +/- 0.83, mean +/- SD) and were significantly decreased after probenecid treatment (1.26 +/- 0.28, P less than 0.01). Probenecid had no effect on GFR, as assessed by inulin clearance. Using the nonspecific picrate assay, CLcr/CLin was 1.12 +/- 0.41, which was not significantly different from unity and which decreased to 0.53 +/- 0.12 after probenecid treatment. Therefore, creatinine undergoes extensive renal secretion in female Lewis rats.

Animals↗
PubMed1991

Reversible compensatory hypertrophy in transplanted brown Norway rat kidneys.

Recently we described methods for optimizing the function of transplanted rat kidneys. In unilaterally nephrectomized recipients, one week after surgery, the left transplanted kidney was identical to the right native kidney with respect to wet weight and the clearances of inulin and para-aminohippuric acid (PAH). The goals of the present experiments were first, to extend the post-surgery period to three weeks (sufficient to allow hypertrophic changes), and second, to study function of transplanted hypertrophied kidneys. Genetically identical Brown Norway rats were used as donor and recipients. Three weeks after transplanting a normal kidney into a unilaterally-nephrectomized recipient, the transplanted kidney had a normal plasma flow and was identical to the contralateral native kidney with respect to wet weight and the clearances of inulin and PAH. Three weeks after transplanting a normal kidney into a bilaterally-nephrectomized recipient, the wet weight, inulin and PAH clearances, and plasma flow of the transplanted kidney were all higher than control, and not significantly different from those observed in unilaterally-nephrectomized control rats. Thus, transplanted and native kidneys exhibited the same degree of compensatory hypertrophy. Hypertrophied donor kidneys (that is, the donor rat had been unilaterally-nephrectomized three weeks previously) remained hypertrophied in bilaterally-nephrectomized recipients, but in unilaterally-nephrectomized recipients, they regressed towards normal (that is, the values of wet weight, inulin and PAH clearances and plasma flow were significantly less than those in rats with only one kidney) while the contralateral native kidney remained normal (values of wet weight and inulin and PAH clearances were not different from control).(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1981

Peritubular interaction of unconjugated bilirubin in isolated perfused rat kidney.

1. The interaction of unconjugated bilirubin with peritubular cell membranes of the rat kidney was studied by means of an isolated rat-kidney preparation applying the multiple-indicator-dilution technique. 2. Inulin was used as an extracellular marker and p-aminohippuric acid as a model of organic anion that interacts with the peritubular membrane. 3. A single renal artery injection of a mixture containing inulin and unconjugated bilirubin was followed by the appearance of the two compounds in the venous effluent. The unconjugated bilirubin curve was always under the curve of inulin and its mean transit time was always less than that of inulin. 4. The cumulative venous recovery of inulin was higher than that of unconjugated bilirubin. 5. When unconjugated bilirubin uptake was plotted against the injected dose of pigment the relationship suggested a saturation phenomenon. 6. The recovery of p-aminohippuric acid was significantly increased when unconjugated bilirubin was added. 7. The results provide evidence for the interaction of unconjugated bilirubin with the peritubular cell membranes of rat kidney.

Animals↗
PubMed2000

Plant fructans stabilize phosphatidylcholine liposomes during freeze-drying.

Fructans have been implicated as protective agents in the drought and freezing tolerance of many plant species. A direct proof of their ability to stabilize biological structures under stress conditions, however, is still lacking. Here we show that inulins (linear fructose polymers) isolated from chicory roots and dahlia tubers stabilize egg phosphatidylcholine large unilamellar vesicles during freeze-drying, while another polysaccharide, hydroxyethyl starch, was completely ineffective. Liposome stability was assessed after rehydration by measuring retention of the soluble fluorescent dye carboxyfluorescein and bilayer fusion. Inulin was an especially effective stabilizer in combination with glucose. Analysis by HPLC showed that the commercial inulin preparations used in our study contained no low molecular mass sugars that could be responsible for the observed stabilizing effect of the fructans. Fourier transform infrared spectroscopy showed a reduction of the gel to liquid-crystalline phase transition temperature of dry egg PtdCho by more than 20 degrees C in the presence of inulin. A direct interaction of inulin with the phospholipid in the dry state was also indicated by dramatic differences in the phosphate asymmetric stretch region of the infrared spectrum between samples with and without the polysaccharide.

Cichorium intybus↗