Showing papers on "Serum albumin published in 1985"

Isolation and partial characterization of a fatty acid binding protein in rat liver plasma membranes

Abstract: When [14C]oleate-bovine serum albumin complexes were incubated in vitro with rat liver plasma membranes (LPM), specific, saturable binding of oleate to the membranes was observed. Maximal heat-sensitive (i.e., specific) binding was 3.2 nmol/mg of membrane protein. Oleate-agarose affinity chromatography of Triton X-100-solubilized LPM was used to isolate a single 40-kDa protein with high affinity for oleate. On gel filtration, the protein comigrated with various fatty acids but not with [14C]bilirubin, [35S]sulfobromophthalein, [14C]taurocholate, [14C]phosphatidylcholine, or [14C]cholesteryloleate. A rabbit antibody to this membrane fatty acid-binding protein gave a single precipitin line with the antigen but no reactivity with concentrated cytosolic proteins, LPM bilirubin/sulfobromophthalein-binding protein, or rat albumin or other rat plasma proteins. The antibody selectively inhibited heat-sensitive binding of [14C]oleate to LPM. Immunofluorescence studies localized the antigen in liver-cell plasma membranes as well as in other major sites of fatty acid transport. These data are compatible with the hypothesis that this protein may act as a receptor in a hepatocellular uptake mechanism for fatty acids.

Clinical Pharmacokinetics of the Salicylates

Abstract: The use of salicylates in rheumatic diseases has been established for over 100 years. The more recent recognition of their modification of platelet and endothelial cell function has lead to their use in other areas of medicine. Aspirin (acetylsalicylic acid) is still the most commonly used salicylate. After oral administration as an aqueous solution aspirin is rapidly absorbed at the low pH of the stomach millieu. Less rapid absorption is observed with other formulations due to the rate limiting step of tablet disintegration - this latter factor being maximal in alkaline pH. The rate of aspirin absorption is dependent not only on the formulation but also on the rate of gastric emptying. Aspirin absorption follows first-order kinetics with an absorption half-life ranging from 5 to 16 minutes. Hydrolysis of aspirin to salicylic acid by nonspecific esterases occurs in the liver and, to a lesser extent, the stomach so that only 68% of the dose reaches the systemic circulation as aspirin. Both aspirin and salicylic acid are bound to serum albumin (aspirin being capable of irreversibly acetylating many proteins), and both are distributed in the synovial cavity, central nervous system, and saliva. The serum half-life of aspirin is approximately 20 minutes. The fall in aspirin concentration is associated with a rapid rise in salicylic acid concentration. Salicylic acid is renally excreted in part unchanged and the rate of elimination is influenced by urinary pH, the presence of organic acids, and the urinary flow rate. Metabolism of salicylic acid occurs through glucuronide formation (to produce salicyluric acid), and salicyl phenolic glucoronide), conjugation with glycine (to produce salicyluric acid), and oxidation to gentisic acid. The rate of formation of salicyl phenolic glucuronide and salicyluric acid are easily saturated at low salicylic acid concentrations and their formation is described by Michaelis-Menten kinetics. The other metabolic products follow first-order kinetics. The serum half-life of salicylic acid is dose-dependent; thus, the larger the dose employed, the longer it will take to reach steady-state. There is also evidence that enzyme induction of salicyluric acid formation occurs. No significant differences exist between the pharmacokinetics of the salicylates in the elderly or in children when compared with young adults. Apart from differences in free versus albumin-bound salicylate in various disease states and physiological conditions associated with low serum albumin, pharmacokinetic parameters in patients with rheumatoid arthritis, osteoarthritis, chronic renal failure or liver disease are essentially the same.(ABSTRACT TRUNCATED AT 400 WORDS)

Serum protein binding of 1,25-dihydroxyvitamin D: a reevaluation by direct measurement of free metabolite levels.

Abstract: Using the technique of centrifugal ultrafiltration isodialysis to measure the free concentration of 1,25-dihydroxyvitamin D [1,25-(OH)2D], we determined the affinity of serum proteins for 1,25-(OH)2D both by Scatchard analysis (increasing ligand concentration at fixed binding site concentrations) and by a novel analysis in which the binding site concentrations were varied (serial dilution) at fixed ligand concentrations. The high affinity binding constant in serum for 1,25-(OH)2D was 3.7 X 10(7) M-1 by Scatchard analysis and 4.2 X 10(7) M-1 by serial dilution analysis. Human serum albumin had a much lower affinity for 1,25-(OH)2D (5.4 X 10(4) M-1). When vitamin D-binding protein (DBP) was selectively removed from serum by an actin affinity column, the affinity of the remaining serum proteins for 1,25-(OH)2D was that of albumin. Postulating a two-site model (DBP and albumin) for transport of 1,25-(OH)2D in serum and incorporating the estimated affinity constants of DBP and albumin for this metabolite, we calculated that 85% of total circulating 1,25-(OH)2D is transported in blood bound to DBP in normal individuals (0.4% is free and 14.6% is bound to albumin). In patients with liver disease, 73% is bound to DBP (1.1% is free and 25.9% is bound to albumin). Using this same two site model, we found a reasonable correlation (r = 0.612; P less than 0.001) between the measured free 1,25-(OH)2D level and the calculated free 1,25-(OH)2D level in serum based on albumin and DBP concentrations in 16 normal subjects and 16 patients with liver disease. These results confirm the concept that although DBP is the principal protein carrier of 1,25-(OH)2D in serum, albumin is a major secondary carrier, especially in patients with low DBP levels.

Albumin-mediated changes in sperm sterol content during capacitation.

Abstract: The role of albumin in mouse sperm capacitation was studied in relation to its activities as a lipid-solubilizing protein and a sterol acceptor. Two bovine serum albumins (BSA) which supported capacitation, Fraction V and fatty acid-free, both contained cholesterol and phospholipid but were without detectable levels of serum high-density lipoprotein (HDL). The lipid content of BSA could be reduced by trichloroacetic acid (TCA) precipitation; however, removal of all detectable lipids required precipitation with ethanolic acetone and diethyl ether extraction. In medium supplemented with Fraction V, fatty acid-free, or TCA-precipitated BSA, mouse sperm were capacitated as evidenced by their ability to fertilize eggs, concomitant with decreases in total cellular sterol and increases in phospholipid content. Delipidated BSA, fractionated on Sephadex G-100 in guanidine HCl also supported capacitation and mediated a 20% decrease in sperm sterol content, while cellular phospholipid levels remained unchanged. When BSA was modified by cholesterol augmentation, fertilization was inhibited in a cholesterol dose-dependent manner. These findings suggest that modulation of sperm lipid levels comprises an event of capacitation and that albumin mediates this process through its activity as a sterol acceptor.

Relationship between gingival crevicular fluid and serum antibody titers in young adults with generalized and localized periodontitis.

Abstract: The objective of the present study was to determine the relationship between concentrations of antibodies in serum and those in gingival crevicular fluid (GCF) of patients with juvenile periodontitis and severe periodontitis. Most antigens used to quantitate antibodies were obtained from a panel of bacteria associated with juvenile periodontitis or severe periodontitis. We further investigated variation in antibody titer among different periodontal sites and the extent to which antibody in GCF is locally derived. Titers of antibody, total immunoglobulin G (IgG), and human serum albumin were determined with sensitive radioimmunoassays. The relationship between serum and GCF antibody was complex. Both person-to-person variability and marked variability within the same subject were found among different sites of similar clinical status. The site-to-site variability was found not only for antibody reactive with periodontal organisms, but also for antitetanus toxoid, total IgG, and even human serum albumin. Generally the variability was in the degree of depression of the level in GCF relative to that in serum. However, anti-Bacteroides gingivalis and anti-Actinobacillus actinomycetemcomitans in GCF often exceeded the level in serum. When antibody titers in serum and GCF were calculated per milligram of human serum albumin, most of the apparent depressions of antibody in GCF disappeared. The ratio of antibody in serum to that in GCF approached unity for all organisms except B. gingivalis and A. actinomycetemcomitans Y4, which were markedly elevated. Furthermore, the level of IgG per milligram of human serum albumin in GCF was about twice the level in serum. We believe that human serum albumin reflects serum contribution to the GCF, and we therefore attribute the increased level of IgG per milligram of albumin in GCF to local synthesis. It appears that anti-B. gingivalis and anti-A. actinomycetemcomitans represent an important portion of this local antibody synthesis, since most seropositive patients with severe or juvenile periodontitis had at least one site elevated, and the magnitudes of the elevations were large in many sites. Those sites yielding elevated antibody exhibited no obvious differences in clinical parameters of probeable depth or attachment level as compared with sites in which antibody levels in GCF were similar to serum levels. Elevated antibody in GCF may relate to changes in disease activity that are not detectable by usual clinical measures.

Improved radioimmunoassay for vitamin D and its use in assessing vitamin D status.

Abstract: We describe a faster, more-sensitive radioimmunoassay for vitamin D in plasma. Antibodies were generated in rabbits immunized with a new vitamin D analog, the 23,24,25,26,27-pentanor-C(22)-carboxylic acid of vitamin D, coupled directly with bovine serum albumin. After several months, Rivanol-treated sera from the rabbits contained high-titer antibodies, as determined by their abilities to bind 25-hydroxy-[3H]cholecalciferol. The antibody, used at a 1:15 000 final dilution, cross reacted equally with all cholecalciferol and ergocalciferol metabolites tested except 1,25-dihydroxycalciferol metabolites and the parent calciferols. 25-Hydroxycalciferol and similar forms were efficiently extracted from plasma or serum with acetonitrile. We separated bound from free 25-hydroxy-[3H]cholecalciferol by using a second antibody: goat antiserum to rabbit serum. The detection limit of the assay was 3.0 pg of 25-hydroxycholecalciferol and its equivalents per tube; thus only 1 microL of plasma is needed per assay tube. Results compared well with those from a liquid-chromatographic procedure involving specific ultraviolet detection of 25-hydroxycalciferol in plasma.

Equilibrium dialysis, ultrafiltration, and ultracentrifugation compared for determining the plasma-protein-binding characteristics of valproic acid.

Abstract: Equilibrium dialysis, ultrafiltration, and ultracentrifugation were compared to determine their reliability and applicability in the study of binding of an anticonvulsant drug, valproic acid, by plasma proteins. We studied drug binding with pooled serum and with solutions of human serum albumin at physiological concentrations. We compared binding characteristics such as number of binding sites, affinity constants, and percent of binding as measured by each method in the therapeutic range for valproic acid. Results by ultracentrifugation differed from those by equilibrium dialysis and ultrafiltration, which agreed reasonably well with each other.

Serum concentrations of vitamin D metabolites in untreated tuberculosis.

Abstract: A prospective study of 50 consecutive patients presenting with tuberculosis has shown that patients have on average lower serum concentrations of 25-hydroxycholecalciferol (25-OHD) than healthy matched controls. No difference was shown in serum 1,25-(OH)2D, 24,25-(OH)2D, or parathyroid hormone. Uncorrected serum calcium was lower in the patient group but identical when correction concentrations were made for albumin. Serum liver enzyme concentrations were significantly higher in the patient population. Low serum vitamin D concentrations may be a consequence of disease. The possibility that low serum 25-OHD concentrations may predispose to tuberculosis infection cannot, however, be excluded. Prolonged treatment with isoniazid or rifampicin, both of which have been shown to reduce serum 25-OHD, may increase the risk of vitamin D deficiency and consequent osteomalacia in groups of patients most at risk, such as those of Indian subcontinental ethnic origin.

Influx of kininogens into nasal secretions after antigen challenge of allergic individuals.

Abstract: We have recently demonstrated that kinins are generated in vivo after nasal challenge with antigen of allergic, but not nonallergic, individuals. The present study was undertaken as a first step in determining the mechanism(s) of kinin formation during the allergic reaction and was directed towards establishing the availability and origin of kininogens in nasal secretions. Allergic individuals (n = 6) and nonallergic controls (n = 5) were challenged with antigen; and by using specific radioimmunoassays, nasal washes, obtained before and after challenge, were assayed for high molecular weight kininogen (HMWK), total kininogen (TK), albumin, and kinins. Dramatic increases in HMWK (1,730 +/- 510 ng/ml), TK (3,810 +/- 1035 ng/ml), kinin (9.46 +/- 1.75 ng/ml), and albumin (0.85 +/- 0.2 mg/ml) were observed after challenge of allergic individuals which correlated (P less than 0.001) with increases in histamine and N-alpha-tosyl-L-arginine methyl esterase activity and with the onset of clinical symptoms. For nonallergic individuals, levels of kininogens, albumin, and all mediators after antigen challenge were not different from base line. Linear regression analysis revealed excellent correlations (P less than 0.001 in each case) between increases in HMWK, TK, kinin, and albumin during antigen titration experiments and between the time courses of appearance and disappearance of HMWK, TK, kinin, and albumin after antigen challenge. Gel filtration revealed no evidence of degradation products of kininogens in nasal washes. For each allergic individual the ratio of HMWK/TK in postchallenge nasal washes was similar to the ratio of these two proteins in the same individual's plasma. These data suggest that, during the allergic reaction, there is an increase in vascular permeability and a transudation of kininogens from plasma into nasal secretions, where they can provide substrate for kinin-forming enzymes.

Relationships between magnesium and protein concentrations in serum.

Abstract: We determined concentrations of magnesium, total protein, albumin, and globulin in more than 74 000 serum specimens from patients and noted a direct linear relationship between the concentration of magnesium in serum and the concentrations of total protein, albumin, and globulin in serum. Albumin and magnesium concentrations are linearly related at high and low albumin concentrations; within the reference interval, however, the magnesium concentration is independent of the albumin concentration. Linear regression analysis suggests that 25% of the total serum magnesium is bound to albumin and 8% to globulins.

Igg Production Within the Central Nervous System – a Critical Review of Proposed Formulae

Abstract: Demonstration of intrathecal IgG production is employed in the diagnosis of various neurological disorders. This pathological IgG fraction in cerebrospinal fluid (CSF) can be visualized directly as oligoclonal bands by electrophoresis or isoelectric focusing or can be calculated as "excess" or "synthesized" IgG according to different formulae. A comparison of the results obtained with isoelectric focusing and with five formulae showed that even though three of the formulae discriminated well between a reference population and patients with multiple sclerosis, all five gave wrong and misleading results in the presence of blood-brain barrier damage, as defined by an abnormally raised CSF/serum albumin ratio. A mathematical and statistical evaluation of the different formulae showed only those based on covariance between CSF/serum IgG and CSF/serum albumin to be valid, and these only when values of CSF/serum albumin were normal. Among the five formulae the IgG index (equal to CSF/serum IgG:CSF/serum albumin) is unique in having a comparatively small and constant maximal relative error resulting from the variation coefficients of the IgG and albumin assays. In the case of blood-brain barrier damage, there exists currently no valid procedure to calculate intrathecally produced IgG; in such instances sensitive electrophoretic or isoelectric focusing methods demonstrating oligoclonal IgG bands are most appropriate to demonstrate intrathecal IgG production.

Uptake of hematoporphyrin derivative by normal and malignant cells: effect of serum, pH, temperature, and cell size.

Abstract: Normal and malignant cells were incubated with hematoporphyrin derivative (HPD) and their uptake and retention of HPD were analyzed by flow cytometry. In standard growth medium the amount of HPD taken up by cells was proportional to the added HPD concentration and reached a plateau level after 5–6 h of incubation. The uptake occurred in two steps; within seconds a large amount of HPD became loosely bound to the cells, presumably the outer membrane. This was followed by a slower uptake of HPD into the cytoplasm. The loosely bound portion could be washed from the cells by medium containing either fetal calf serum or serum albumin. At low temperatures the uptake into the cytoplasm was strongly reduced. A major determinant of HPD uptake was the concentration of serum in the medium. At any particular concentration of HPD below 200 mg/liter, increasing concentrations of fetal calf serum or bovine serum albumin resulted in a reduction in the amount of HPD taken up by cells. A further factor affecting uptake was the pH of the medium. At low pH (pH 6) the rate of HPD incorporation was much higher than at pH 7.4. Under identical conditions of incubation, HPD uptake was proportional to cell size as estimated using the low angle light scatter signal in the flow cytometer. Our data suggest that acidic pH, differences in extracellular serum concentrations of malignant tumor tissue, as well as the increased size of tumor cells may play an important role in the selective uptake of HPD by malignant tumors.

In vitro and in vivo synthesis of the hepatitis B virus surface antigen and of the receptor for polymerized human serum albumin from recombinant human adenoviruses

Abstract: We have developed an adenovirus vector to express foreign proteins under the control of the adenovirus E1a promoter. Two recombinant plasmids, harbouring either the S gene or the pre-S2 region and the S gene of hepatitis B virus under the control of the E1a promoter, were used to construct two recombinant adenoviruses. These two viruses direct the synthesis of hepatitis B virus surface antigen (HBsAg) particles during the time course of an infectious cycle. When the pre-S2 region is present in the constructed virus, the synthesis of particles carrying the receptor for polymerized human serum albumin (pHSA) is observed. Moreover, the inoculation of rabbits with this latter purified recombinant adenovirus elicits the production of antibodies that react with both HBsAg and pHSA receptor.

Relations between high-affinity binding sites of markers for binding regions on human serum albumin.

Abstract: Binding of warfarin, digitoxin, diazepam, salicylate and Phenol Red, individually or in different pair combinations, to defatted human serum albumin at ligand/protein molar ratios less than 1:1 was studied at pH 7.0. The binding was determined by ultrafiltration. Some of the experiments were repeated with the use of equilibrium dialysis in order to strengthen the results. Irrespective of the method used, all ligands bind to one high-affinity binding site with an association constant in the range 10(4)-10(6) M-1. High-affinity binding of the following pair of ligands took place independently: warfarin-Phenol Red, warfarin-diazepam, warfarin-digitoxin and digitoxin-diazepam. Simultaneous binding of warfarin and salicylate led to a mutual decrease in binding of one another, as did simultaneous binding of digitoxin and Phenol Red. Both effects could be accounted for by a coupling constant. The coupling constant is the factor by which the primary association constants are affected; in these examples of anti-co-operativity the factor has a value between 0 and 1. In the first example it was calculated to be 0.8 and in the latter 0.5. Finally, digitoxin and salicylate were found to compete for a common high-affinity binding site. The present findings support the proposal of four separate primary binding sites for warfarin, digitoxin (and salicylate), diazepam and Phenol Red. An attempt to correlate this partial binding model for serum albumin with other models in the literature is made.

Scavenger receptor-mediated recognition of maleyl bovine plasma albumin and the demaleylated protein in human monocyte macrophages.

Abstract: Maleyl bovine plasma albumin competed on an equimolar basis with malondialdehyde low density lipoprotein (LDL) in suppressing the lysosomal hydrolysis of 125I-labeled malondialdehyde LDL mediated by the scavenger receptor of human monocyte macrophages. Maleyl bovine plasma albumin, in which 94% of the amino groups were modified, exhibited an anodic mobility in agarose electrophoresis 1.7 times that of the native protein. Incubation of maleyl bovine plasma albumin at pH 3.5 regenerated the free amino groups and restored the protein to the same electrophoretic mobility as native albumin. The demaleylated protein suppressed 75% of the hydrolysis of 125I-labeled malondialdehyde LDL and greater than 80% of 125I-labeled maleyl bovine plasma albumin. The ability of the demaleylated protein to compete was abolished after treatment with guanidine hydrochloride. Although ligands recognized by the scavenger receptor typically are anionic, we propose that addition of new negative charge achieved by maleylation, rather than directly forming the receptor binding site(s), induces conformational changes in albumin as a prerequisite to expression of the recognition domain(s). The altered conformation of the modified protein apparently persists after removal of the maleyl groups. We conclude that the primary sequence of albumin, rather than addition of new negative charge, provides the recognition determinant(s) essential for interaction of maleyl bovine plasma albumin with the scavenger receptor.

Identification and clinical significance of allergenic molecules of cat origin. Part of the DAS 76 Study.

Abstract: Freeze-dried extracts from cat dander and the corresponding rabbit antibodies were used for establishing the CIE reference pattern for cat dander extracts. Anti-Cat Ag 1 and anti-cat albumin were used for identification of the corresponding antigens. CRIE on sera from selected groups of American and Danish cat-allergic patients demonstrated antigen-specific IgE binding to 10 of 15 cat dander antigens (Cat Ag 1 being the major allergen). Only minor differences were found between the two groups. Four of these allergens were serum proteins. Variable amounts of many of the 10 allergens were measured by QIE in saliva, serum, urine and three cat pelt extracts. However, extremely wide ranges for content of the serum allergens and the non-serum allergens were found. This was exemplified by an albumin/cat Ag 1 ratio between 1 and 400, smallest in cat dander. Immunoabsorption using anti-cat dander, anti-cat albumin and anti-Cat Ag 1 indicated that the anti-cat dander, anti-cat albumin, and the anti-Cat Ag 1 absorbed approximately 90%, 25%, and 56%, respectively, of the dander RAST activity, and 87%, 11%, and 45%, respectively, of the saliva RAST activity, confirming the major importance of Ag 1. It is concluded that cat allergenic extracts should contain only modest amounts of serum albumin and other serum-derived antigens and that any relevant standardization must include quantification of at least Cat Ag 1 and cat albumin.

The Estimation of Serum Fructosamine: An Alternative Measurement to Glycated Haemoglobin

Abstract: A method is presented for the estimation of fructosamine using a Cobas Bio centrifugal analyser. The effect of three different preparations of human serum albumin used for construction of calibration curves of 1-deoxy-1-morpholinofructose is described. The selection of serum albumin and the concentration used in the standard solutions is critical since the dose-response curve is affected differently and will therefore influence the estimated values. Normal ranges were obtained for non-diabetic subjects with normal protein status and for a group of females with reduced albumin levels due to pregnancy or oestrogen therapy. There was no significant difference between fructosamine levels in these populations. Fructosamine was also estimated in 250 patients attending a diabetic out-patient department and this correlated well with haemoglobin A1 estimated simultaneously. The method is rapid, technically simple and inexpensive and may prove to be a useful and reliable alternative to HbA1 estimation.

Absence of albumin receptor on brain capillaries in vivo or in vitro

Abstract: Hormones and drugs are known to be available for transport into brain and liver in vivo from the circulating albumin-bound pool. An albumin receptor-mediated mechanism is one possible way in which the transport of ligands from the circulating albumin-bound pool into the tissue may be catalyzed. The albumin receptor model was tested for brain in the present studies using both 125I-albumin (labeled by lactoperoxidase) and [3H]albumin (labeled by reductive methylation). The interaction of the labeled albumin with brain capillaries was assessed in vivo with the carotid injection technique in rats and in vitro with isolated bovine brain capillaries. Artifactually high nonspecific binding in both the in vivo and in vitro assays was observed with 125I-albumin. Conversely, the transit time of [3H]albumin through the brain capillaries in vivo was no greater than the transit time of [14C]sucrose. The binding of [3H]albumin to isolated microvessels in vitro was low, less than [3H]inulin and was nonsaturable. In conclusion these studies do not support the albumin receptor model for the transport of albumin-bound ligands into tissues such as brain.

Nutrition in patients undergoing orthotopic liver transplant.

Abstract: Thirteen patients with severe liver disease had nutritional assessment in the weeks prior to orthotopic liver transplantation. Parameters measured included height and weight, upper arm anthropometry, delayed cutaneous hypersensitivity, total lymphocyte count, serum levels of albumin and transferrin, and plasma amino acids. Weight, when expressed as a percentage of ideal body weight, was greater than 85%, considered the normal lower limit, in all but two patients. However, mean triceps skinfold and arm muscle circumference were 49 ± 25 and 78 ± 9% standard, respectively. Mean serum albumin was 2.7 ± 0.6 g/dl and although mean serum transferrin level was 184 ± 86, eight patients had levels less than normal. Seven patients were anergic to Multitest CMI (58%) and 12 patients had depressed total lymphocyte count. All these later measurements in the aggregate support a diagnosis of protein-calorie malnutrition. High preoperative levels of amino acids, especially aspartate, phenylalanine, tyrosine, and methionin...

Hemagglutination assay of polypeptide coded by the pre-S region of hepatitis B virus DNA with monoclonal antibody: correlation of pre-S polypeptide with the receptor for polymerized human serum albumin in serums containing hepatitis B antigens.

Abstract: The receptor for polymerized human as well as chimpanzee serum albumins has been identified on the 55-amino acid polypeptide coded by the pre-S region of hepatitis B virus DNA. Monoclonal antibodies were raised against a synthetic polypeptide of 19 amino acid residues representing a hydrophilic region of the pre-S amino acid sequence deduced from hepatitis B virus DNA. Sheep erythrocytes fixed with glutaraldehyde were coated with monoclonal antibody against the synthetic polypeptide to develop a hemagglutination assay for pre-S polypeptide. The pre-S polypeptide was detected in the serum containing hepatitis B surface antigen particles along with hepatitis B e antigen, with titers in parallel with those of the receptor for polymerized human serum albumin.

Interaction of furosemide with serum thyroxine-binding sites: in vivo and in vitro studies and comparison with other inhibitors.

Abstract: The diuretic furosemide inhibits serum protein binding of T4 in equilibrium dialysis, dextran-charcoal, and competitive ligand binding separation systems and displaces [125I]T4 from isolated preparations of T4-binding globulin (TBG), prealbumin, and albumin. Equilibrium dialysis studies of undiluted normal serum showed that about 10 micrograms/ml furosemide increased the free T4 and free T3 fractions. Displacement occurred at lower drug concentrations in sera with subnormal albumin and TBG levels. Binding of [14C]furosemide to TBG was inhibited by unlabeled T4, suggesting that furosemide and T4 share a common binding site. A single oral dose of 500 mg furosemide given to five patients maintained on peritoneal dialysis increased the percentage of charcoal uptake of [125I]T4 (using serum diluted 1:10) from 4.1 +/- 1.0 (+/- SE) to 10.8 +/- 4.3 (P less than 0.01) after 2 h, while decreasing total T3 from 75 +/- 5 to 56 +/- 13 ng/dl (P less than 0.01) and total T4 from 6.7 +/- 0.9 to 4.8 +/- 0.8 micrograms/dl (P less than 0.01) after 5 h. Various ligands inhibited [125I]T4 binding to serum proteins in the following relative molar relationship: T4, 1; furosemide, 1.5 X 10(3); fenclofenac, 2 X 10(4); mefenamic acid. 2.5 X 10(4); diphenylhydantoin, 4 X 10[4); ethacrynic acid, 10(5); heparin 5 X 10(5); 2-hydroxybenzoylglycine, 10(6); and sodium salicylate, 1.5 X 10(6). These studies demonstrate that furosemide competes for T4-binding sites on TBG, prealbumin, and albumin, so that a single high dose can acutely lower total T4 and T3 levels. The drug is much more potent on a molar basis than other drug inhibitors of T4 binding, but at normal therapeutic concentrations, furosemide is unlikely to decrease serum T4 or T3. However, high doses, diminished renal clearance, hypoalbuminemia, and low TBG accentuate its T4- and T3-lowering effect. Hence, furosemide should be considered a possible cause of low thyroid hormone levels in patients with critical illness. The significance of this drug in reports of impaired hormone and drug binding in renal failure requires further assessment.