Recovery Of Inulin Research Articles

Response Surface Optimization of Inulin and Polyphenol Extraction from Artichoke (Cynara scolymus (L.)) Solid Wastes

Artichoke wastes after processing represent 60–70% of the raw material and are a potential source of inulin and polyphenols, bioactive compounds that can be valorized as food ingredients or nutraceutical products. The aim of this work was to assess and optimize the extraction of these compounds from artichoke wastes using water or water–ethanol mixtures as extracting agents. For simultaneous inulin and polyphenol extraction and to achieve high antioxidant activity in extracts, the best process conditions using water as an extracting agent were T = 89 °C and t = 139 min, where 80% of the inulin content, 60% of the total phenolic content (TPC) and 56% of the antioxidant activity (Aox) were obtained. For water–ethanol extractions, the best results were obtained with EtOH = 22.4%, T = 81 °C and t = 217 min, leading to extraction yields of 90% of TPC, 38% of Aox and 58% of inulin content. From these results, we recommend the use of water for the recovery of inulin and polyphenols from artichoke wastes. Although the extraction yield of polyphenols is lower in water treatments, the amount extracted is considerable and it is a greener option when compared with water–ethanol mixtures.

Inulin extraction from common inulin-containing plant sources

Currently there is a growing interest from the food industry in obtaining inulin for its possible use in the elaboration of functional foods. A set of optimum extraction conditions was developed for the recovery of inulin plus fructo-oligosaccharides (FOS) from several common inulin-containing plant sources, like chicory roots (Cichorium intybus L.) and Jerusalem artichoke tubers (Helianthus tuberosus L.), as well as from novel sources like globe artichoke inflorescence (Cynara cardunculus L.) and its by-product. Optimal conditions for temperature (60−80 °C), time (20−60 min) and solvent to solid ratio (10−40 mL/g) were estimated in order to maximize inulin plus FOS extraction by using response surface methodology (RSM) with a Box-Behnken design. Inulin plus FOS were estimated colorimetrically by difference between total carbohydrate and reducing sugar contents for the optimization. Moreover, the profile of inulin and low molecular weight carbohydrates was studied in optimized plant extracts by HPLC. Inulin in raw samples and optimal extracts were further characterized by Fourier Transformed Infrared spectroscopy. According to response surface methodology model, optimal conditions for inulin plus FOS extraction depended on plant source and were achieved at a solvent to solid ratio of 27.8–37.4 mL/g, from 62−80 °C and a variable time of 22−60 min. The highest inulin plus FOS contents were achieved in chicory root (70.5 g/100 g dry weight) and Jerusalem artichoke tuber (81.1 g/100 g dry weight), and the lowest ones were attained in globe artichoke by-product (4.2 g/100 g). Nevertheless, its high availability and low cost would support this novel globe artichoke by-product as an alternative and valuable source of inulin and FOS for the food industry. At the same time their reuse as potential prebiotic ingredients would contribute to the circular economy.

Data of co-extraction of inulin and phenolic compounds from globe artichoke discards, using different conditioning conditions of the samples and extraction by maceration

The current data presented correspond to the determination of inulin recovery from globe artichoke canned industry wastes. The discard was composed mainly by bracts with a small percentage of stems and receptacles. Artichoke discards (AD) were dehydrated by lyophilization or convective drying at different temperatures (40°C to 100°C). Inulin amount in extracts obtained using hydroalcoholic solvents (ethanol:water 75:25), which are applied for polyphenols recovery, was determined. After that, the sequential extraction of inulin with water and then with hydroalcoholic solvent was done. Finally, inulin content in lyophilized samples using different ethanol:water mixtures was determined. Inulin was determined by vanillin method and total phenolic compounds (TPC) by Folin-Ciocalteu method. From the lyophilized sample it is possible to obtain 3938.7 ± 169.1 mg inulin / 100 g AD dry basis (d.b.) and 2086.3 ± 120.7 mg TPC / 100 g AD d.b. While, from conventionally dried samples, the recovery of inulin can reach 4391.1 ± 208.2 mg inulin / 100 g AD d.b for samples dried at 60°C, but only 337.2 ± 25.9 mg TPC / 100 g AD d.b. was recovered at the same condition. Sequential extraction of lyophilized samples with water (95°C, 30 minutes) and ethanol:water 75:25 (40°C, 60 minutes) recovers in total 10907.3 mg inulin / 100 g AD and 2687.7 mg TPC / 100 g AD d.b. If the ethanol concentration decreases at 50% and the extraction is done only with the hydroalcoholic solvent, the inulin increases up to 5251.2 ± 257.4 mg inulin / 100 g AD d.b.This Data in Brief corresponds to an accompanying work to the article titled “Valorization of Globe Artichoke (Cynara scolymus) Agro-Industrial Discards, Obtaining an Extract with a Selective Effect on Viability of Cancer Cell Lines” published at Processes journal [1].

Recent insights for the green recovery of inulin from plant food materials using non-conventional extraction technologies: A review

Abstract Inulin constitutes an important food ingredient, widely used for its fiber content, and its ability to substitute fat and sugar ingredients. Traditionally, industrial inulin production from chicory roots requires high extraction temperature (70–80 °C) and long extraction time (1–2 h). This conventional extraction is generally accompanied with the presence of a large amount of impurities in the extracted juice, mainly due to the application of high temperature, requiring thus further purification steps. To overcome these issues, developing novel extraction technologies, consuming less energy, faster, and providing high yield and purity, is of paramount importance to meet the requirements of a green extraction concept. In this review, the feasibility of using conventional and new promising technologies (enzyme assisted extraction, ultrasounds, microwaves, supercritical fluid extraction, and pulsed electric fields) to recover inulin from plant food materials and by-products from an environmental and economical point of view will be discussed. Industrial relevance Inulin is widely used in food industries mainly due to its ability to substitute fat and sugar ingredients. However, the current industrial recovery process of this molecule is mainly carried out by diffusion in hot water (70–80 °C), followed by a relatively complex purification process, due to the presence of a large amount of impurities generated by the application of high temperatures. The need for obtaining greener, sustainable, and viable processes has led food scientists to develop new processes in full correspondence with the green extraction concept based on the use of non-conventional technologies (i.e. pulsed electric fields, ultrasounds, microwaves, etc). The submitted review discusses the potential of some of these new promising technologies to allow the industrial sustainability and green recovery of inulin, which have as benefits: energy- and time-saving along with higher yields and milder temperatures, reducing thus the subsequent purification steps.

DETERMINATION OF INULIN FROM MULTIVITAMIN SYRUP PRODUCT BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY WITH RI DETECTOR

At present, inulin is often added to multivitamin syrup product. The determination of the component of preparation both qualitatively and quantitatively is important to ensure quality of the product. This research is aimed to develop a high performance liquid chromatography method to analyze inulin in multivitamin syrup preparation. Separation of inulin from the sample, was performed using Aminex column HPX-87H (300 x 7.8 mm) Ion Exclusion at a temperature of 80 °C with isocratic elution system using deionized water as mobile phase at a flow rate of 0.5 mL/min, and detected by using refractive index detector. This method validation showed a good linearity with correlation coefficient (r) of 0.999 while the coefficient of variation of the regression function (Vx0) was 2.00%. The limit of detection (LOD) and the limit of quantification (LOQ) of the method were respectively 0.12 mg/mL and 0.37 mg/mL. The mean absolute recovery of inulin from the simulation sample was 99.42% and the method precision was less than 2%. The proposed method has been applied to the determination of inulin in commercial multivitamin syrup and the recovery of label claim was 99.9 mg/100 mL. The proposed HPLC method is rapid, simple, and selective for routine analysis.

DETERMINATION OF INULIN FROM MULTIVITAMIN SYRUP PRODUCT BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY WITH RI DETECTOR

At present, inulin is often added to multivitamin syrup product. The determination of the component of preparation both qualitatively and quantitatively is important to ensure quality of the product. This research is aimed to develop a high performance liquid chromatography method to analyze inulin in multivitamin syrup preparation. Separation of inulin from the sample, was performed using Aminex column HPX-87H (300 x 7.8 mm) Ion Exclusion at a temperature of 80 °C with isocratic elution system using deionized water as mobile phase at a flow rate of 0.5 mL/min, and detected by using refractive index detector. This method validation showed a good linearity with correlation coefficient (r) of 0.999 while the coefficient of variation of the regression function (Vx0) was 2.00%. The limit of detection (LOD) and the limit of quantification (LOQ) of the method were respectively 0.12 mg/mL and 0.37 mg/mL. The mean absolute recovery of inulin from the simulation sample was 99.42% and the method precision was less than 2%. The proposed method has been applied to the determination of inulin in commercial multivitamin syrup and the recovery of label claim was 99.9 mg/100 mL. The proposed HPLC method is rapid, simple, and selective for routine analysis.

Evaluation of a new automated, enzymatic inulin assay using d-fructose dehydrogenase

Inulin clearance (Cin) is widely considered to be a gold-standard assessment of glomerular filtration rate (GFR). Although inulin concentrations are commonly determined by the anthrone method, this method has several disadvantages, including a hazardous heating procedure using a strong acid, as well as a nonspecific reaction and being influenced by other saccharides such as glucose. Here, we report the development of a new automated, enzymatic inulin assay. This method uses D: -fructose dehydrogenase (EC1.1.99.11), which does not require NAD or NADP as the electron acceptor, and utilizes oxygen transfer from hydrogen peroxide to an electron acceptor in a sensitive chromophoric system. This method allows rapid and accurate determination of inulin concentrations, and takes only 15 min on automated analyzers. We evaluated this new assay and compared it with the anthrone method. The detection limit value and linearity of the new method were 5 mg/l and up to 300 mg/l, respectively. The within-run precision coefficient of variations (CVs) for serum and for urine were 2.05 +/- 0.79% (mean +/- SEM; n = 3) and 0.92 +/- 0.24%, respectively, and the between-run precision CVs for serum and for urine were 1.91 +/- 0.72% and 1.86 +/- 0.17%, respectively. No influence of glucose was observed with the new method, while a positive influence of 38.7% was observed with the anthrone method. However, neither method was influenced by fructose (3.0 mg/l in serum or 30 mg/l in urine). The analytical recovery rates of inulin were 97.8 +/- 0.7% (mean +/- SEM; n = 6) in serum and 99.0 +/- 0.4% in urine using the enzymatic method. We compared results for the enzymatic method and the anthrone method using 46 serum samples and 46 urine samples. Bland-Altman plots showed no significant difference between the two methods for the serum samples. However, inulin recovery in the urine samples measured by the enzymatic method was about 5% higher than that obtained by the anthrone method. The new enzymatic assay offers a more convenient and more accurate measurement of inulin and may be suitable for routine procedures by automated analyzers in clinical laboratories.

Preparation of inulin and phenols-rich dietary fibre powder from burdock root

The simultaneous ultrasonic/microwave assisted extraction (UMAE) of inulin and production of phenols-rich dietary fibre powder from burdock root was studied. It was found that UMAE required a much shorter extraction time than conventional stirring extraction. And the recovery of inulin increased with the increase of microwave power as well as solvent to solid ratio. A comparison of scanning electron microscopy images of raw and simultaneous ultrasonic/microwave treated burdock root indicated microfractures and disruption of cell walls in burdock root flakes. The dietary fibre powder prepared from the residue of burdock root after inulin extraction was rich in phenols (302.62 mg GAE/100 g powder). The results showed that drying temperature in the selected range did not significantly affect the hydration properties. The relatively high water retention capacity, swelling capacity and oil-holding capacity of the dietary fibre powder indicated its broad use as a modifier of properties of formulated products.

Enzymatic determination of inulin and fructooligosaccharides in food

Inulin and fructooligosaccharides (FOS) are widely distributed throughout the plant kingdom. They have been increasingly used in various foods due to their beneficial nutritional attributes. An enzymatic method was developed for rapid and accurate determination of inulin and/or FOS in food. s-Fructofuranosidase heterologously expressed in Escherichia coli was used as a hydrolyzing enzyme. After extraction with water, filtration and appropriate dilution, inulin was hydrolyzed using s-fructofuranosidase and the liberated sugars were determined enzymatically. The average recovery of inulin and/or FOS in food matrixes was 97% with a coefficient of variation of 5%. The method provided an inexpensive technique requiring only standard laboratory equipment for determining inulin and/or FOS with high accuracy and precision.

Recovery of inulin from Jerusalem artichoke (Helianthus tuberosus L.) in the small intestine of man

The recovery of inulin, a naturally occurring beta (2-->1)-fructan isolated from Jerusalem artichoke (Helianthus tuberosus L.), in the small intestine of man was studied in ileostomy subjects. The ileostomists were given a low-dietary-fibre diet based on white wheat bread and virtually free of inulin, and the same diet with the addition of 10 g and 30 g inulin product respectively, and the recovery and mean transit time (MTT) of inulin were estimated by tracking inulin in ileal effluent. The recovery of inulin was approximately 87% at both ingestion levels. MTT was 4.9 (SE 0.6) h at an intake of 10 g inulin product decreasing to 3.4 (SE 0.3) h at an intake of 30 g inulin product. A significant change in the fructose:glucose ratio of inulin from ingestion (4.1) to recovery in ileal effluent (4.5-4.7) and a lower recovery of the glucose residue than of the fructose residue of inulin indicate that the low-molecular-weight inulins are more sensitive to hydrolysis than the high-molecular-weight fragments. The loss of inulin during passage through the small intestine is presumably due to hydrolysis by either acids or enzymes and to microbial degradation by the microflora permanently colonizing the distal small intestine. The concentrations of lactic acid (LA) and short-chain fatty acids (SCFA) in frequently collected ileal effluents on the control day were approximately 6 nmol/l and approximately 55 mmol/l respectively. During periods with inulin ingestion the concentration of LA increased to 18-26 mmol/l (P < 0.052), while the concentration of SCFA ran converse and decreased to 18-32 mmol/l (P < 0.023). The osmotic loads (68 and 204 mosmol/l) associated with the ingestion of inulin product caused minor malabsorption of low-molecular-weight sugars.

Effects of tenoxicam on renal function and the disposition of inulin and p‐aminohippurate in healthy volunteers and patients with chronic renal failure.

1. The effects of tenoxicam on renal function were studied in 10 patients with chronic renal failure (creatinine clearance 46.7 +/- 11.9 ml min-1 1.73 m-2) and eight healthy volunteers. A parallel treatment control group of eight healthy volunteers received placebo. Tenoxicam was given orally in a dose of 40 mg daily for 2 days followed by 20 mg daily for a further 8 days. Renal function was assessed by measurement of the renal clearances of inulin and p-aminohippurate (PAH) using the single injection technique before and during administration of tenoxicam. 2. In the healthy volunteers there were no changes in glomerular filtration rate, effective renal plasma flow, or the urinary excretion of N-acetylglucosaminidase and beta 2-microglobulin on the 3rd and 10th days of treatment with tenoxicam. The mean urinary excretion of prostaglandins E2 and 6-keto F1 alpha decreased during treatment but there was great individual variation and the differences were not statistically significant. Tenoxicam had no effect on the half-life, clearance, volume of distribution or urinary recovery of inulin and PAH. 3. There was no significant change in the clearance of inulin and creatinine after treatment with tenoxicam for 10 days in the patients with chronic renal failure. However, in this group there was a significant increase in plasma creatinine on the 3rd and 6th days with a return to pretreatment levels by the 10th day. The administration of tenoxicam for 10 days was associated with a small but significant increase in the plasma half-life and volume of distribution of inulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of acid disposal and acid-stimulated alkaline secretion by gastroduodenal mucosa.

This paper investigates acid disposal by gastric and duodenal mucosa with particular reference to the mechanisms of acid-stimulated luminal alkalinization in the duodenum. The bulk of solute flux across duodenal epithelium occurs by paracellular permeation, and passive diffusion of HCO3 via shunt pathways contributes substantially to luminal alkalinization by this tissue in vitro. Effects on epithelial permeability of two treatments which stimulate mucosal alkaline secretion (PGE2 and low luminal pH) were studied in vivo by measuring transmucosal fluxes of radiolabeled urea (mol wt 76) and inulin (mol wt approximately 5000). Rats were anesthetized and rates of alkalinization in segments of distal duodenum perfused with saline were monitored by continuous titration. PGE2 (10 microM, topically) increased alkaline secretion from 1.63 +/- 0.34 to 3.07 +/- 0.54 microeq/cm/hr (mean +/- SEM, N = 5). Luminal acid exposure (10 mM HCl for 10 min) increased alkalinization rate from 1.54 +/- 0.43 to 2.69 +/- 0.76; subsequent addition of PGE2 induced a further rise to 3.27 +/- 0.54. Recovery of inulin in the luminal perfusate following intravenous injection was less than 10% of that of urea. Topical PGE2 had little or no effect on recovery of either marker. Luminal acidification increased the rate of appearance of urea by 130 +/- 30% (P less than 0.01, N = 6); recovery of inulin rose slightly but did not achieve statistical significance compared with control. Thus stimulation of mucosal alkaline secretion by luminal PGE2 or acid are associated with differential effects on mucosal permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting proximal tubular reabsorption during development.

Studies performed in several animal species have demonstrated that glomerulotubular balance is maintained throughout development despite the many changes that occur in the factors known to control it. In an attempt to understand the nature of this phenomenon we quantified the magnitude and described the profile of these changes in guinea pigs. The changes in physical forces were assessed from measurements of hydrostatic and oncotic pressures, whereas those in the permeability characteristics of the proximal tubule epithelium were estimated from permeance to macromolecules of graded radii, histologic measurements of the intercellular channels, and measurements of end-proximal ratio of tubular fluid-to-plasma osmolality (TF/Posm). Between 1 and 50 days of age the net pressure for reabsorption increased from 15.0 to 30.9 mmHg (P less than 0.01, n = 15) with the major change occurring during the first 2-3 wk of postnatal life. The urinary recovery of inulin, sucrose, and creatinine, injected in the early segment of proximal tubules did not vary with age. The urinary recovery of mannitol (MW 180 daltons, Stokes-Einstein radius 4.0 X 10(-10) m) increased from 92% at birth to 100% at 49 days of age (P less than 0.001, n = 24), consistent with a decrease of approximately 0.5 X 10(-10) m in the luminal openings of the paracellular channels. The length of the zonulae occludens and the width of the intercellular channels did not change during this period; however, the length of the channels increased from 5.0 +/- 0.17 to 8.9 +/- 0.48 micron (P less than 0.01, n = 16). These changes should result in an increase in resistance across the intercellular channels. Consistent with this assertion is the observation that the mean TF/Posm of the fluid collected toward the end of the proximal convoluted tubule decreased as a function of age from 1.05 at day 2 to 0.98 at day 80 (P less than 0.001, n = 24). The findings support the hypothesis that during early postnatal life glomerulotubular balance is made possible by a high permeability of the proximal tubule, which compensates for the low net reabsorptive pressure. As the animal matures and the proximal tubule epithelium becomes tighter, for glomerulotubular balance to be maintained, an increase in the number of intercellular channels and in the active transport of sodium need to be postulated.

Intestinal Absorption of Biotin in the Rat

We examined the absorption of biotin using the in vivo intestinal loop technique. Jejunal segments from male rats were filled with solutions containing [3H]biotin and [14C]inulin in Krebs-Ringer phosphate buffer, pH 6.5. Absorption was determined on the basis of luminal tritium disappearance after correction for inulin recovery. At biotin concentrations of 0.1 and 5.0 µM, luminal biotin disappearance was linear for at least 10 min. At biotin concentrations ranging from 2.3 nM to 75 µM, 10–28% of the administered dose was absorbed in 10 min. The concentration dependence of luminal biotin disappearance is consistent with the presence of both saturable and nonsaturable (linear) components of biotin uptake, with estimated Km = 9.6 µM and Jmax = 75.2 pmol/(2.5 cm loop · min). The rate constant for nonsaturable uptake is 3.1 pmol/(2.5 cm loop · min · µM). We conclude that at biotin concentrations less than 5 µM, biotin absorption proceeds largely by the saturable process, whereas at concentrations above 25 µM, nonsaturable uptake predominates. Additional studies demonstrated significantly less biotin uptake in the ileum than in the jejunum, a finding in agreement with previous in vitro studies.

Modification of biliary tree permeability in rats treated with a manganese-bilirubin combination

Previous studies in this laboratory demonstrated incorporation of manganese (Mn) and bilirubin (BR) in rat liver bile canalicular membrane (BCM) following a cholestatic regimen composed sequentially of Mn plus BR. The present study investigates biliary tree permeability using segmented retrograde intrabiliary injection (SRII) with [ 3H]mannitol and [ 3H]inulin as marker substances. Male Sprague-Dawley rats were given the following iv: (a) Mn (high and low dose), (b) BR, (c) sulfobromophthalein (BSP), (d) Mn-BSP-BR, (e) MnBR. Results obtained with mannitol showed a ∼63% decrease ( p < 0.05) in marker recovery following administration of MnBR combination. While BSP alone had no effect on mannitol recovery, BSP abolished the MnBR response when administered in the Mn-BSP-BR sequence. With inulin, Mn (high dose), MnBR, and Mn-BSP-BR all produced a ∼45% decrease ( p < 0.05) in recovery, while BSP or BR alone caused a ∼25% decrease ( p < 0.05). Mn (low dose) was without effect. These results and others obtained when the time pattern of the MnBR treatment was modified suggest: (1) MnBR treatment increases biliary tree permeability by altering both BCM and the junctional complex; (2) BCM alteration is probably the more critical event, since BSP, which protects against MnBR cholestasis, protected against the MnBR-induced change in mannitol recovery, but exerted no effect on inulin recovery.

Human complement protein D catabolism by the rat kidney.

Factor D (D) is an essential component of the alternative complement pathway. To determine whether D is catabolized by the kidney and, if so, at what site, we studied the renal handling of human D by in vivo nephron microperfusion and in vitro perfusion of rat kidneys. Human D was purified and labeled with 125I. Individual nephrons were perfused in vivo at varying rates with perfusate that contained 125I-D and [14C]inulin. When nephrons were perfused from proximal sites with perfusate 125I-D in a concentration of 3.0 micrograms/ml, urinary recovery of 125I-D increased (P less than 0.05) from 57.7 +/- 5.0 to 74.4 +/- 2.5% as tubule fluid flow rate was increased from 10 to 40 nl/min; recovery of 125I-D was less than (P less than 0.001) [14C]inulin recovery at all perfusion rates. At 20 nl/min, an increase in perfusate 125I-D concentration from 1.5 to 3.0 micrograms/ml was associated with an increase (P less than 0.001) in urinary 125I-D recovery (42.1 +/- 4.0 vs. 65.8 +/- 2.6%). Similarly, the addition of unlabeled D, 30 micrograms/ml, to 125I-D, 3.0 micrograms/ml, increased urinary 125I-D recovery (95.3 +/- 2.1%) at 20 nl/min. When nephrons were perfused from early distal segments at 10 nl/min, 125I-D recovery (91.2 +/- 4.3%) did not differ from [14C]inulin recovery (95.8 +/- 1.3%). In the isolated perfused filtering kidney, the concentration of intact 125I-D in the perfusate declined 60.3 +/- 14.6% over 1 h. 83.4 +/- 6.3% of the decrement in 125I-D was catabolized by the kidney; the remainder was excreted in the urine as intact D. When glomerular filtration was prevented by increasing perfusate albumin concentration to 16 g/dl, perfusate intact (125I-D) remained unchanged over 1 h. These data show that human D is catabolized by the kidney via glomerular filtration and reabsorption by the proximal nephron. Reabsorption of D appears to be a saturable process.

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.

638 THE RENAL HANDLING OF 3-METHYLHISTIDINE

The urinary excretion of the unique amino acid, 3-methylhistidine (3MH), has been proposed as a marker of endogenous protein catabolism and an index of a patient's metabolic state. Yet, the mechanisms of the renal handling of 3MH remain unclear. Consequently, we determined the simultaneous clearance of 3MH (C3MH) and inulin (Cin) in rats. Net reabsorption of 3MH was a consistent finding. In ten euvolemic animals, C3MH (313.2 ± 37.5 μl/min/100g BW) was less than Cin (1017.1 ± 21.2) and the percent 3MH reabsorbed was 72.6 ± 3.7%. In five volume expanded animals, the percent 3MH reabsorbed was not significantly altered (80 ± 5.0%). To confirm net reabsorption, 3MH combined with inulin was microinjected into proximal tubules of surface nephror Inulin recovery from the microinjected kidney averaged 102 ± 5% while the recovery of 3MH was only 74 ± 6% (P < 0.01). The percent of 3MH reabsorbed had no relationship to the quantity of 3MH injected, suggesting that there is no Tm for 3MH. This study clearly demonstrates that: 1) the renal clearance of 3MH is less than that of inulin, 2) net tubular reabsorption occurs over a wide range of filtered loads of 3MH and 3) a Tm for reabsorption of this amino acid metabolite could not be documented. These factors must be considered in using urinary excretion of 3MH as a marker of nutritional status.

Evidence for renal tubular leakage in maleic acid-induced Fanconi syndrome.

Micropuncture and microinjection studies were performed in Sprague-Dawley rats 20 h after subcutaneous injection of buffered maleic acid (MA) or buffer alone in experimental and control rats, respectively. Collections were made from earliest and latest accessible portions of proximal tubule (PT). Lissamine green injections and microperfusion of PT demonstrated leakage of lissamine green from late PT sites in MA-treated rats, whereas inulin leakage occurred at a more distal site. Whole kidney GFR was 58% lower in MA-treated rats despite comparable single nephron GFR in PT of both groups. Microinjections of PT with [methoxy-3H]inulin resulted in injected inulin recovery from the contralateral kidney in MA-treated rats of 24.0 +/- 2.0 compared with 4.7 +/- 0.89% in controls, suggesting that tubular leakage of inulin accounted for the lower whole kidney GFR. Net sodium and phosphate transport in early PT was similar in both groups but was decreased in late PT segments in MA-treated rats. Sodium and phosphate excretion in final urine were, however, comparable in both groups. The significantly lower plasma phosphate concentration might account for the blunted phosphaturia in MA-treated rats. These studies demonstrate a segmental effect of MA on 1) tubular leakage to lissamine green from late PT and inulin beyond the late PT, and 2) decreased net sodium and phosphate transport in the PT.

Renal tubular transport of 3H-digoxin in saline diuresis in rats.

We evaluated urinary excretion and tubular transport of 3H-digoxin by three different methods in anesthetized rats made diuretic by infusion of 2.5% saline. In one group small volumes of 3H-digoxin and 14C-inulin were injected simultaneously into surface proximal convolutions, and urine was collected serially from both ureters. Digoxin recovery was lower after early (62.1 +/- 5.3%) than after late (86.9 +/- 7.7%) proximal administration but inulin recovery was complete (99.6 +/- 2.7%) after all injections. Most of the digoxin was excreted simultaneously with inulin. Delayed recovery was low. In another group of rats digoxin and inulin were applied directly to the capsule of the left kidney. Two-thirds of the recovered digoxin appeared from the left ureter and one-third from the right. The difference (41.9 +/- 7.4%) is an estimate of transtubular digoxin influx. Digoxin excretion preceded inulin only on the left. Digoxin to inulin concentration ratios were 6 times higher from the left than the right, whereas inulin recoveries from the two sides were similar. In a third group of rats tubular fluid was collected from surface convolutions of proximal and distal tubule. In the accessible segment of the proximal tubule 35.9% of the filtered digoxin was reabsorbed. In the more distal nephron, drug was added into the lumen; this resulted in a net urinary excretion of 80.2 +/- 18.2%. These findings are compatible with free filtration of digoxin at the glomerulus followed by passive proximal tubular reabsorption and an influx against a concentration gradient in the distal nephron.