Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Ultrafiltration”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
PubMed1993

Pharmacokinetic monitoring in subcutaneous tissue using in vivo capillary ultrafiltration probes.

Capillary ultrafiltration probes were utilized for in vivo sampling of therapeutic drugs in awake rats. Capillary ultrafiltration probes implanted into subcutaneous tissue were able to follow the disposition of acetaminophen and theophylline. Ultrafiltration probes provided samples at a rate of 2-3 microL/min. Ultrafiltrates were analyzed by liquid chromatography with either UV or electrochemical detection. Simultaneous ultrafiltration and microdialysis probes and multiple ultrafiltration probes were used in individual animals to validate the technique. The pharmacokinetics of two well-established drugs, acetaminophen and theophylline, were monitored in awake, freely moving rats to demonstrate the viability of the technique. The half-life for acetaminophen was determined to be 20.9 +/- 1.0 min (n = 6) for a 2 mg/kg dosing. The half-life of elimination for theophylline was determined to be 3.0 +/- 0.1 hr (n = 4) for a 4 mg/kg dose. The capillary ultrafiltration probes exhibited a constant flow rate of 2.4 +/- 0.1 microL/min and removed 50 nL/min/mm of fluid from the extracellular space. Capillary ultrafiltration sampling is shown to be an excellent tool for in vivo monitoring of drug disposition and a suitable method for determining pharmacokinetic parameters in awake animals.

Acetaminophen↗
PubMed1999

Uremic ultrafiltrate inhibits platelet-activating factor synthesis.

BACKGROUND: Several studies have suggested that uremic toxins may adversely affect phagocytic leukocytes of chronic renal failure patients. Platelet-activating factor (PAF) is produced by phagocytic leukocytes and is a potent mediator of inflammation which is produced by leukocytes upon appropriate stimulation. METHODS: We added uremic or normal ultrafiltrate, ultrafiltrate fractionated by reverse phase HPLC or compounds eluting at the same retention time as the fractionated ultrafiltrate, to normal leukocytes. Complement-coated baker's yeast spores were added to stimulate phagocytosis. Total PAF was purified by thin layer chromatography and quantified by bioassay on rabbit platelets. The activities of two enzymes involved in the synthesis of PAF, phospholipase A2 (PLA2) and acetyltransferase, were measured in the presence of fractionated ultrafiltrate. RESULTS: Ultrafiltrate from both healthy and uremic subjects inhibited PAF synthesis, but the inhibitory effect was more substantial for uremic subjects. Ultrafiltrate fractionated by HPLC showed high PAF inhibition for late eluting hydrophobic fractions. Addition of phenol or p-cresol, two uremic toxins with similar elution pattern as the late fractions, also inhibited PAF synthesis. The activity of PLA2 and acetyltransferase was decreased in the presence of uremic ultrafiltrate. CONCLUSIONS: We observed that uremic ultrafiltrate inhibits PAF synthesis upon stimulation with complement coated baker's yeast spores. The decrease in total PAF synthesis appears to be associated with an inhibition of phospholipase A2 and acetyltransferase activity, enzymes involved in the remodelling pathway for PAF synthesis.

Adult↗
PubMed2001

Mechanism of bovine serum albumin aggregation during ultrafiltration.

Protein fouling is a critical problem for ultrafiltration. In this study, we adopted bovine serum albumin (BSA) as a model protein and polysulfone membrane as a typical ultrafiltration membrane. We then investigated the factors of the protein denaturation and aggregation, such as stirring shear stress and intermolecular exchange of disulfide during ultrafiltration, and discussed the BSA fouling mechanism. Fourier transform-infrared analysis revealed that magnetic stirring did not cause any difference in the secondary structural change of BSA gel-like deposits on the ultrafiltration membrane. BSA aggregates were collected from BSA gel-like deposits on the ultrafiltration membrane by centrifugation. Polyacrylamide gel electrophoresis in SDS analysis of BSA aggregates proved that the major binding of the BSA aggregates involved intermolecular disulfhydryl binding and that capping the free thiol group in BSA molecules with cysteine induced a remarkable decrease in the amount of the BSA aggregates during ultrafiltration. We concluded that one of the main factors in the BSA aggregation during ultrafiltration is the intermolecular exchange of disulfide through cysteinyl residue. We also found that the BSA aggregation caused a decrease in alpha-helix from 66% to 50% and an increase in beta-sheet from 20% to 36%, which was presumably because the cysteine residues associated with the intermolecular disulfide bonds had been located in alpha-helices.

Animals↗
PubMed1975

3H-inulin and electrolyte concentrations in Bowman's capsule in rat kidney. Comparison with artificial ultrafiltration.

Micropuncture experiments were performed on Bowman's capsules in male and female non-diuretic Munich rats. 55 samples were collected and analysed for Na, Cl, K, Ca, P, Mg and 3H-inulin contents. Their electrolyte concentrations were compared to the corresponding concentrations obtained from plasma artificial ultrafiltrates. Compared to normal Wistar rats, our Munich rats had several special characteristics: high arterial pressure (115-155 mm Hg), high concentrating ability (phi equals 2684 mOsm/1) and high NaCl reabsorption capacity. Whole kidney GFR was low in males (0.361 ml/min/kidney/100 g B.W.). 3H-Inulin concentration was the same in plasma and glomerular ultrafiltrates (GF). The corresponding ratio (GF/P) in equals 1.03 plus or minus 0.01 (N equals 55) confirmed the lack of sieving effect for inulin. GF electrolyte concentrations were, for Na, Cl, K, Ca, P, Mg respectively 139 plus or minus 0.05, 1.46 plus or minus 0.07 and 0.52 plus or minus 0.04 ml/1 (N equals 23) in females and 141 plus or minus 2, 120 plus or minus 2, 3.84 plus or minus 0.07, 1.31 plus or minus 0.03, 1.78 plus or minus 0.05 and 0.48 plus or minus 0.01 mM/1 (N equals 32) in males. Comparison of ultrafiltration trough a cuprophan membrane and glomerular ultrafiltration led to the following conclusions: For Na, Cl and P artificial and glomerular ultrafiltration produced identical results. On the other hand, for Ca and to a lesser extent for Mg and K ions, artificial ultrafiltration did not accurately reflect the true glomerular ultrafiltrate composition. The reasons for these differences are discussed below.

Animals↗
PubMed1998

Effects of cardiopulmonary bypass and use of modified ultrafiltration.

BACKGROUND: Hemodilution is a prominent problem in cardiopulmonary bypass in a pediatric population. Ultrafiltration is a method used to reduce fluid volume and tissue edema and to increase hematocrit without the need for blood products. Modified ultrafiltration may offer advantages in comparison with conventional ultrafiltration. METHODS: This article reviews the technique of modified ultrafiltration and its use, results, complications, and safety in pediatric cardiopulmonary bypass. RESULTS: Modified ultrafiltration in pediatric cardiopulmonary bypass reduces total body water and serum levels of inflammatory mediators. It results in an elevated hematocrit without the need for transfusion, improved pulmonary compliance in the immediate postbypass period, and probably improved cerebral metabolic recovery after deep hypothermic circulatory arrest. CONCLUSIONS: Modified ultrafiltration can be performed safely in neonatal patients after cardiopulmonary bypass and offers advantages in comparison with conventional ultrafiltration.

Adolescent↗
PubMed1999

Glomerular ultrafiltration of IGF-I may contribute to increased renal sodium retention in diabetic nephropathy.

Insulin-like growth factor-I (IGF-I) is found in plasma at relatively high levels (approximately 40 nmol/L) but <1% is present in the free form and >99% is bound to specific binding proteins to form high-molecular-weight complexes of approximately 50 and approximately 150 kd. We hypothesized that in rats with diabetic nephropathy but not in normal animals, IGF-I-containing binding protein complexes undergo glomerular ultrafiltration, allowing the peptide to interact with IGF-I receptors in apical tubular membranes. By this route, ultrafiltered IGF-I may increase tubular epithelial cell sodium absorption in overt diabetic nephropathy. In serum samples from diabetic rats, IGF-I levels (227 +/- 34 ng/mL) were reduced as compared with control levels (319 +/- 33 ng/mL, P = .05), and IGF-binding protein-2 (IGFBP-2) is increased about 2-fold. In diabetic rats, IGF-I undergoes glomerular ultrafiltration and is present in proximal tubular fluid that was collected by nephron micropuncture at 2.54 +/- 0.54 nmol/L but is below the detection limit in tubular fluid from normal rats. IGFBP-1, IGFBP-2, IGFBP-3, and IGFBP-4 are all present in diabetic rat glomerular ultrafiltrate, but IGFBP-2 levels are greater than those of each of the other three IGFBPs. Neither recombinant human IGF-I (1 nmol/L) nor diabetic rat glomerular ultrafiltrate affect sodium transport in cultured mouse proximal tubular cells. In contrast, rhIGF-I and diabetic rat glomerular ultrafiltrate increase the apical-to-basolateral transport of 22Na+ in distal tubule-like A6 cells through mechanisms involving apical IGF-I receptors. In normal rats, luminal infusion with rhIGF-I or with diabetic rat glomerular ultrafiltrate into late proximal tubules increases distal tubular Na+ absorption. These findings indicate that diabetic glomerular sclerosis causes glomerular ultrafiltration of IGF-I, and they suggest that tubular fluid IGF-I may contribute to sodium (and fluid) retention that is commonly observed in patients with severe diabetic nephropathy.

Animals↗
PubMed1993

Can ultrafiltration occur with a hypo-osmolar solution in peritoneal dialysis?: The role for 'colloid' osmosis.

1. In peritoneal dialysis the removal of excess body water (ultrafiltration) is traditionally achieved by means of dialysis solution made hypertonic to plasma by the addition of an osmotic agent. In vitro, the osmotic flow may be directed against the osmolality gradient by using a hypo-osmolar solution, but this phenomenon has not previously been applied to clinical peritoneal dialysis. 2. The ultrafiltration performances of hypo-osmolar dialysis solutions containing a high-molecular-weight glucose polymer (weight average molecular weight 22,000), isolated by fractionation of hydrolysed corn starch, were compared with those of hypertonic glucose solutions over a 12 h exchange in 11 patients well established on continuous ambulatory peritoneal dialysis. 3. Five per cent (272 +/- 1.1 mosmol/kg) and 7.5% (277 +/- 2.0 mosmol/kg) glucose polymer solutions produced net ultrafiltration of 243 +/- 53 and 526 +/- 59 ml that were significantly greater than the ultrafiltration of -48 +/- 96 and 223 +/- 84 ml associated with 1.36% (339 +/- 1.9 mosmol/kg) and 2.27% (393 +/- 3.2 mosmol/kg) glucose solutions, respectively. The net ultrafiltration with 10% glucose polymer (284 +/- 2.0 mosmol/kg) and 3.86% glucose (482 +/- 1.6 mosmol/kg) solutions were similar (699 +/- 48 versus 708 +/- 82 ml). 4. The transperitoneal absorption of glucose polymer was substantially lower than that of glucose solutions as was the potential calorie load per millilitre of ultrafiltrate. 5. The addition of 0.35% glucose (molecular weight 180) to 7.5% glucose polymer solution raised the dialysate osmolality to an iso-osmolar level (299 +/- 0.8 mosmol/kg) and produced ultrafiltration which was 29% greater than with 7.5% glucose polymer solution alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2001

Prevention of haemodialysis-induced hypotension by biofeedback control of ultrafiltration and infusion.

BACKGROUND: Haemodialysis-induced hypotension is still a severe complication in spite of all the progress in haemodialysis treatment. Because of its multifactorial causes, haemodialysis-induced hypotension cannot be reliably prevented by conventional ultrafiltration and sodium profiling in open-loop systems, as they are unable to adapt themselves to actual decreases in blood pressure. METHODS: A blood-pressure-guided closed-loop system, for prevention of haemodialysis-induced hypotension by biofeedback-driven computer control of both ultrafiltration and saline infusion was clinically tested in 237 treatments of seven patients prone to hypotension. As medical knowledge on multifactorial causes of hypotension is characterized by a lack in deterministic knowledge, fuzzy logic and linguistic variables were used to involve clinical experience on hypotension phenomena in terms of fuzzy knowledge. Biofeedback control is based on frequent measurements of blood pressure at 5 min intervals. Blood pressure behaviour is described by linguistic variables and fuzzy sets. Adaptive rule bases were used for the simultaneous fuzzy control of both the ultrafiltration and infusion of hypertonic saline (20% NaCl). Proper adaptation of control features to patient's conditions was provided by the critical borderline pressure, which was set by the physician individually at the beginning of each treatment. During the initial and medium phases of the sessions, ultrafiltration rates up to 150% of the average rates were applied as long as decreases in blood pressure could be compensated by saline infusion. The surplus of ultrafiltrate volume was used for blood pressure stabilization in the final phase in most instances by low ultrafiltration rates. RESULTS: The advantages of biofeedback-controlled haemodialysis were demonstrated by both decreasing the frequency of hypotonic episodes and by increasing or maintaining constant levels of systolic blood pressure during the final phase in 88% of treatments. As saline infusion was applied mainly in the initial and medium phases, blood sodium levels were not significantly higher at the end of the sessions, and interdialytic weight gain was not elevated. CONCLUSION: The application of fuzzy logic in the blood-pressure-guided biofeedback control of ultrafiltration and sodium infusion during haemodialysis is able to minimize haemodialysis-induced hypotension.

Biofeedback, Psychology↗
PubMedDate not supplied

Plasma refilling during hemodialysis with decreasing ultrafiltration. Influence of dialysate sodium.

Inadequate plasma refilling is an important determinant of vascular instability during hemodialysis. Hypotension is more frequent toward the end of dialysis, as the patient reaches dry weight. This study compared plasma volume changes in 12 patients dialyzed with constant ultrafiltration and a constant dialysate Na of 140 mEq/L (Group A), sequentially decreasing ultrafiltration (50% in first hour, 30% in the second hour, and 20% in the third hour) using constant dialysate Na (Group B), and sequentially decreasing ultrafiltration with sequentially decreasing dialysate Na from 150 to 140 mEq/L (Group C). All of the patients had midweek dialysis with each protocol. Blood pressure, hematocrit, blood urea nitrogen, serum osmolality, and albumin were determined before and hourly thereafter. Ultrafiltration was constant at 12.2 ml/min in Group A but 18.4 ml/min in the first hour, 11.0 in the second hour, and 7.3 in the third hour in Groups B and C. In Group A, plasma volume did not change during the first hour but decreased in the second and third hours (4.9%). In Group B, plasma volume decreased during the first and second hours 5.6% but slightly increased during the third hour 5.3%, whereas in Group C, plasma volume increased during the first hour (2.1%), was unchanged during the second hour, and decreased 1.2% during the third hour. These data suggest that plasma refilling is enhanced during hemodialysis using sequentially decreasing ultrafiltration and high-to-low dialysate Na (Group C); this strategy may be preferred to hemodialysis with constant dialysate Na and ultrafiltration (Group A) or sequentially decreasing ultrafiltration with constant dialysate Na (Group B) when improvement in vascular stability is needed.

Aged↗
PubMed2005

Effect of ultrafiltrate volume on determination of free phenytoin concentration.

Monitoring free phenytoin concentration is clinically useful for patients with uremia, hepatic disease, hypoalbuminemia, and related conditions. Free phenytoin is commonly measured by immunoassay in the protein-free ultrafiltrate prepared by centrifuging serum for 20-30 minutes, using an appropriate ultrafiltration device. We studied the effect of centrifugation time (15-40 minutes) and protein concentrations on ultrafiltration volume, and the related effects on measured free phenytoin concentrations. Temperature was ambient for all studies. The ultrafiltration volumes were directly proportional to centrifugation time and were inversely proportional to the protein concentrations. Although ultrafiltration volume significantly increased with longer centrifugation time, the measured free phenytoin concentrations did not increase proportionately. The concentration of phenytoin in the residual serum retained in the ultrafiltration device did not change proportionally either. Therefore, equilibrium of phenytoin concentrations between the ultrafiltrate and retentate was maintained, regardless of centrifugation time or protein concentration.

Blood Proteins↗
PubMed1982

Dialyzer ultrafiltration coefficients: comparison between in vitro and in vivo values.

This study describes a simple, convenient method for the in vivo measurement of the ultrafiltration coefficient of hemodialyzers. The method is based on a scheme of isolated ultrafiltration, i.e., ultrafiltration without dialysate flow through the dialyzer. Results with this method indicate that it is more accurate than the conventional bed scale technique. Measurements on three different dialyzers demonstrate that the in vivo ultrafiltration coefficient is only between 1% and 10% lower than the corresponding in vitro value. This is in contrast to the rule of thumb used by some manufacturers that in vivo coefficients are 30% lower than in vitro values. The deviation of the in vivo value from the in vitro one seems to be higher with higher dialyzer ultrafiltration coefficients. Based on these results, it is recommended that to estimate ultrafiltration rates in the clinical setting, the in vitro ultrafiltration coefficient be used, transmembrane pressures being corrected for the colloid osmotic pressure of plasma proteins.

Blood↗
PubMed1995

Influence of hydration state on plasma volume changes during ultrafiltration.

To assess the influence of hydration state on plasma volume (PV) changes during ultrafiltration, 11 clinically normhydrated patients on maintenance hemodialysis were studied intraindividually during 2 hydration states differing by 2-15% of lean body mass (LBM). Plasma volume was measured continually during a 15-min ultrafiltration test including an ultrafiltration of 1% of target weight and during a 45-min follow-up period of blood recirculation through the dialyzer without ultrafiltration. In all patients a maximal decrease in relative PV was more pronounced when there was less hydration and when the grade of hydration correlated inversely with the maximal response of PV decrease (r = -0.68, p < 0.001). The same was observed between the hydration state and the slope of the PV decrease (r = -0.69, p < 0.001). Plasma refilling was estimated in the period following ultrafiltration. The slope of the plasma volume increase correlated with the grade of hydration (r = 0.31, p < 0.05) as did the asymtote of PV (r = 0.4, p < 0.01). It is concluded that the less hydrated a dialysis patient is, the more pronounced will be the fall of the ultrafiltration-induced plasma volume and the less distinct will be the recovery of the plasma volume after the discontinuation of ultrafiltration.

Adult↗
PubMed1990

Ultrafiltration devices tested for use in a free thyroxine assay validated by comparison with equilibrium dialysis.

A new ultrafiltration method for measuring serum free thyroxine (FT4) is presented. The method makes use of disposable ultrafiltration devices, which were selected on grounds of their ability to produce protein-free serum ultrafiltrates necessary for accurate determination of FT4. Ultrafiltrate thyroxine was measured by radio-immunoassay. As measured by this method, the mean serum FT4 concentration in reference subjects (n = 17) was 25.4 pmol/l (SD 7.8). Two patient groups were studied: hyperthyroid (n = 20, mean serum FT4 138 pmol/l, SD 69) and hypothyroid (n = 18, mean serum FT4 14.8 pmol/l, SD 6.5). These results were compared with serum FT4 concentrations, as measured by an ultrafiltration method based on the use of dialysis-tubing bags (r = 0.97), and by an equilibrium dialysis method (r = 0.95). The mean level of FT4, as measured by the ultrafiltration methodologies, was about twice as high as that measured by equilibrium dialysis. This new FT4 method is more practical than earlier ultrafiltration methods and, theoretically, analytically more accurate than equilibrium dialysis methods.

Blood Proteins↗
PubMed1998

Elevated 24-hour blood pressure in peritoneal dialysis patients with ultrafiltration failure.

Many patients treated with peritoneal dialysis (PD) are overhydrated. We investigated whether hypertension in PD patients is related to ultrafiltration-failure-induced fluid retention. Twenty-four-hour blood pressure measurements were performed in 10 normotensive and 9 hypertensive PD patients, aged 20 to 77 years, and treated with PD for 2 to 125 months. Antihypertensive medication had been discontinued for 3 weeks. Twenty-four-hour blood pressure was monitored with a Spacelabs 90207. Mean 24-hour systolic, mean, and diastolic pressure were calculated, together with the nighttime (23:00-07:00)/daytime (07:00-23:00) ratio. Ultrafiltration was determined separately during a standardized 4-hour peritoneal permeability analysis (SPA) with 1.36% glucose. Based on the SPA, patients were divided into a group with negative net ultrafiltration (NUF) and a group with positive net ultrafiltration (PUF). In 8 patients with NUF, systolic, mean, and diastolic pressures were 142 +/- 16 mmHg, 110 +/- 14 mmHg, and 95 +/- 13 mmHg, compared to 135 +/- 22 (ns), 99 +/- 14 (ns), and 81 +/- 11 (P < 0.05) in 11 patients with PUF. Net ultrafiltration during the test dwell correlated negatively with diastolic blood pressure (r = -0.53, P < 0.05). Diurnal blood pressure variations were not related to ultrafiltration capacity. In conclusion, hypertension in PD patients may in part be explained by fluid retention caused by impaired ultrafiltration.

Adult↗
PubMed1992

Intraperitoneal administration of phosphatidylcholine improves ultrafiltration in continuous ambulatory peritoneal dialysis patients.

Reports in the literature have linked a low phosphatidylcholine content in continuous ambulatory peritoneal dialysis (CAPD) effluent to ultrafiltration loss. Clinical evidence suggests that adding phosphatidylcholine to the dialysis solution enhances ultrafiltration. A clinical study has been designed to clarify the effect of phosphatidylcholine on ultrafiltration in CAPD patients with normal ultrafiltration. A weekly measurement of the peritoneal equilibration test was conducted per patient in the hospital. A comparison between the control dialysis solution (three-week period) and the phosphatidylcholine premixed solution (three-week period) was performed on a total of 12 patients. This study shows that a phosphatidylcholine premixed dialysis solution significantly enhances ultrafiltration. Since ultrafiltration per osmotic driving force (mL/g glucose) is enhanced, the patient's glucose load per day is reduced to achieve equal ultrafiltration. In the presence of phosphatidylcholine, peritoneal permeability remained unchanged, as indicated by membrane transport characteristics. No side effects were observed.

Biological Transport↗
PubMed1978

Comparison of polymer, glucose, and hydrostatic pressure induced ultrafiltration in a hollow fiber dialyzer: effects on convective solute transport.

Ultrafiltration induced by (1) poly(sodium acrylate), (2) glucose, and (3) hydrostatic pressure was studied in a hollow fiber dialyzer. Poly(sodium acrylate) added to dialysate induced large amounts of ultrafiltration without crossing the dialyzer membrane. Sodium ions of the acrylate polymer were osmotically active but were held in dialysate by the impermeant anionic polymer. The hydrostatic pressure equivalent of osmotic pressure induced primarily by the sodium ions approximated that predicted for a completely impermeant molecule. The apparent (net) sieving coefficients for vitamin B12 observed during polymer and hydrostatic ultrafiltration studies were both significantly higher than that observed during glucose ultrafiltration but did not differ from each other. These studies suggest that sodium salts of polyanions can provide an osmotic driving force to yield large amounts of ultrafiltration in dialysis systems and yet not cross the membrane. The studies also suggest that relatively less efficient convective transport with glucose as compared to hydrostatic pressure is neither a membrane phenomenon nor a characteristic of all osmotic pressure induced ultrafiltration. Relatively low effective solute sieving appears to be associated with osmotic induced ultrafiltration with a permeant solute. Under such conditions it is proposed that molecular interaction within the membrane impairs convective transport.

Acrylic Resins↗
PubMed1981

Multilaboratory evaluation of an ultrafiltration procedure for high density lipoprotein cholesterol quantification in turbid heparin-manganese supernates.

High density lipoprotein (HDL) can be quantitated by measurement of cholesterol in supernates after precipitation of low and very low density lipoprotein (LDL and VLDL) with heparin and Mn(2+). Supernatant turbidity, often observed with hypertriglyceridemic specimens, indicates incomplete sedimentation of LDL/VLDL and precludes accurate quantitation of HDL. Ten Lipid Research Clinic Laboratories compared an ultrafiltration technique for clearing turbid heparin-Mn(2+) supernates to current methods involving repeat precipitation of either the original specimen after dilution or the d > 1.006 g/ml fraction after removal of VLDL from the initial specimen by ultracentrifugation. Results for ultrafiltration of 429 turbid supernates averaged only slightly higher (1.0-1.1 mg/dl) than results by the dilution or ultracentrifugation methods on the same specimens, but this difference was found to be significant (P < 0.005). The agreement of the ultrafiltration method with the other two methods is indicated by the following linear regression equations: a), ultrafiltration = (0.964 x ultracentrifugation) + 2.4 mg/dl, and correlation coefficient = 0.926; and b), ultrafiltration = (0.936 x dilution) + 3.3 mg/dl, and correlation coefficient = 0.933. We conclude that ultrafiltration of turbid heparin-Mn(2+) supernates is a convenient alternative to precipitation after either dilution or removal of VLDL.-Warnick, G. R., J. J. Albers, P. Bachorik, J. Turner, C. Garcia, C. Breckinridge, K. Kuba, S. McNeely, G. Hillerman, P. King, R. Muesing, B. Most, and K. Lippel. Multi-laboratory evaluation of an ultrafiltration procedure for high density lipoprotein cholesterol quantification in turbid heparin-manganese supernates.

Chemical Phenomena↗
PubMed1998

Metabolic screening using on-line ultrafiltration mass spectrometry.

An on-line mass spectrometric method has been developed to generate and identify drug metabolites formed by hepatic cytochromes P450. This method, pulsed ultrafiltration-mass spectrometry, may be used for rapid screening of drugs to determine their extent of metabolism by microsomal cytochromes P450 and to characterize the primary metabolites. Rat liver microsomes were trapped in a stirred ultrafiltration chamber fitted with a 100,000 molecular weight cut-off ultrafiltration membrane. A continuous-flow of ammonium acetate buffer was pumped through the chamber and into an electrospray mass spectrometer. Substrates for cytochromes P450 including imipramine, chlorpromazine, and pentoxyresorufin were flow injected through the chamber along with the cofactor, NADPH, and metabolites were detected on-line by using electrospray mass spectrometry. Identical control experiments carried out using boiled microsomes or without NADPH showed no metabolite formation. Naringenin and quinidine, which are inhibitors of some isozymes of cytochrome P450 and are not known to be extensively metabolized, showed no major metabolites. For comparison, imipramine metabolites were also generated by standard batch incubation with microsomes and NADPH, followed by extraction and LC-MS analysis. Similar metabolites were obtained using the flow-through ultrafiltration method and the standard batch microsomal incubation. Tandem mass spectrometry was used to confirm structures of imipramine metabolites including 10-hydroxyimipramine, 2-hydroxyimipramine, imipramine N-oxide, and N-desmethylimipramine. Finally, the feasibility of using ultrafiltration mass spectrometry for high throughput metabolic screening was demonstrated by using on-line mass spectrometry for only 3 min per incubation instead of monitoring the entire elution profile. By carrying out multiple ultrafiltration experiments in parallel, efficient use of the mass spectrometric detector may be obtained with a throughput of at least 20 incubations per hour. Throughputs of up to 60 profiles per hour should be possible. On-line ultrafiltration electrospray mass spectrometry offers a streamlined, higher-throughput method for in vitro formation and mass spectrometric characterization of microsomal drug metabolites.

Animals↗