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R Valdes

Publications and source records attributed to R Valdes.

At least 91 records · Page 5Linked to original sources
PubMed1983

An endogenous digoxin-like substance in patients with renal impairment.

Digoxin concentrations were measured in serum samples from 102 patients with renal impairment who were receiving digoxin therapy. Many patients had values that differed widely on several currently available immunoassays, with differences as great as 2.9 ng/mL. In contrast, patients with normal renal function who were receiving digoxin had few discrepant results, with the largest difference being 0.5 ng/mL. We also assayed serum samples from 54 patients with renal impairment not on digoxin therapy and found that more than 60% of these digoxin-free patients had false-positive digoxin values on most assays. Our data suggest that a substance with digoxin-like immunoactivity is present in many patients with renal insufficiency. This substance may seriously compromise the accuracy and interpretation of digoxin concentration measurements.

Creatinine↗
PubMed1983

Three commercial methods for serum ferritin compared and the high-dose "hook effect" eliminated.

We evaluated four commercial kits for measuring serum ferritin, based on three techniques: immunoradiometric assay, radioimmunoassay, and enzyme immunoassay. The kits evaluated were those manufactured by Abbott Laboratories, Clinical Assays, Corning Medical, and Ramco. Two of the immunoradiometric kits showed satisfactory results with respect to sensitivity and precision; they should be useful in diagnosing individuals with uncomplicated iron-deficiency anemia. One of the immunoradiometric assay kits, however, showed a high-dose "hook effect," beginning at 10 mg of ferritin per liter. We modified this kit to eliminate this effect, at least to ferritin concentrations of 33 mg/L. (We observed a ferritin value as high as 47 mg/L in one patient.) Results with all these kits did not inter-compare well for ferritin concentrations greater than 300 micrograms/L, a finding that casts further doubt on the controversial use of serum ferritin measurement in cases of iron overload.

Anemia, Hypochromic↗
PubMed1982

Comparison of RIA and IRMA methods for measurement of carcinoembryonic antigen (CEA).

We present data comparing the Roche CEA radioimmunoassay (RIA) utilizing ultrafiltration and the Abbott CEA immunoradiometric assay (IRMA) methods for standard curve sensitivity, analytical reproducibility, recovery (pre and post extraction), dilution linearity, and patient correlation. The Roche intra- and inter-assay precision figures for this assay were 8% and 15%, respectively, for a CEA concentration of 4.0 ng/mL. The Abbott assay gave comparable precision values of 9% and 16%, respectively, for a CEA concentration of 2.0 ng/mL. Recovery for plasma spiked with CEA stock preparations was commercial-source-dependent when assayed by the Roche assay, but independent when measured by the Abbott assay. The Roche assay did not recover both preparations quantitatively, while the Abbott assay did. Plasma dilution studies over a wide range of CEA concentrations gave linear results for both assays provided the Roche assay utilizes the extraction method with dialyzate dilution for CEA values greater than 20 ng/mL. A difference (60%) was observed in linear regression slopes of the measured values between the Roche "indirect" and "direct" assays. Exposure of CEA to perchloric acid seems to play a critical role in recovery of CEA material when assayed by the Roche method. A large number of the patient samples assayed gave widely discrepant results when comparing the RIA to the IRMA methods. The potential significance of these discrepancies is discussed.

Carcinoembryonic Antigen↗
PubMed1982

Infantile hypophosphatasia: enzyme replacement therapy by intravenous infusion of alkaline phosphatase-rich plasma from patients with Paget bone disease.

Enzyme replacement therapy for a severely affected 6-month-old girl with hypophosphatasia was attempted by repeated intravenous infusions of alkaline phosphatase-rich plasma, obtained by plasmapheresis, from two men with Paget bone disease. Circulating Paget AP activity was found to have a half-life (two days) similar to that reported in adults, which did not change during a five-week period of six AP infusions. Normalization of the patient's serum AP activity was followed by better control of her hypercalcemia and hypercalciuria. Sequential radiographic studies revealed arrest of worsening rickets with slight remineralization of metaphyses, although urinary excretion of the AP substrates phosphoethanolamine and inorganic pyrophosphate was unaltered by therapy. Our findings suggest that the infantile form of hypophosphatasia results from defective production of AP rather than from accelerated destruction of circulating enzyme, and that hydrolysis of AP substrates like PEA and PPi occurs primarily in tissue rather than blood. Study of additional cases of hypophosphatasia will be necessary to assess the clinical efficacy of this form of enzyme replacement therapy.

Alkaline Phosphatase↗
PubMed1982

Heparin interferes with the radioenzymatic and homogeneous enzyme immunoassays for aminoglycosides.

Heparin interferes with measurement of aminoglycosides in serum by biological, radioenzymatic, and homogeneous enzyme immunoassay techniques, but not with radioimmunoassay. At concentrations greater than or equal to 10(5) and greater than or equal to 3 X 10(6) USP units/L, respectively, it interferes with the radioenzymatic assay by inhibiting the gentamicin 3-acetyltransferase (EC 2.3.1.60) and kanamycin 6'-acetyltransferase (EC 2.3.1.55) enzymes used in the assay. It interferes with the homogeneous enzyme immunoassays for gentamicin and tobramycin (at concentrations greater than or equal to 10(5) and greater than or equal to 10(4) USP units/L, respectively), but not with the commercially available homogeneous enzyme immunoassays for other drugs. Heparin interference with the homogeneous enzyme immunoassay for aminoglycosides requires both the heparin polyanion and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) bound to a cationic aminoglycoside. This interference can be reproduced with dextran sulfate (but not dextran), and does not occur with free enzyme (glucose-6-phosphate dehydrogenase) alone. We describe how heparin interferes with these two assays and demonstrate interference at heparin concentrations that may be present in intravenous infusions or in seriously underfilled blood-collection tubes.

Amikacin↗
PubMed1980

Prolongation of canine pancreas allograft survival with cyclosporin A: preliminary report.

Studies were conducted on dogs to test the efficacy of cyclosporin A (CyA) in prolonging normoglycaemia and graft survival after whole-organ pancreas allograft transplantation. Five dogs subjected to pancreatectomy alone served as controls. Withholding immunosuppression after transplantation (five animals) resulted in the same median duration of survival as occurred in the controls (13 days). Azathioprine and steroids (seven animals) produced median durations of normoglycaemia and survival of 9 and 23 days respectively. Animals given CyA 18 mg/kg/day (five) and 25 mg/kg/day (10), however, showed median durations of normoglycaemia of 18 and 55 days (p less than 0.05 and p less than 0.02) respectively and median survival times of 36 and 85 days (NS and p less than 0.02). If CyA proved effective in controlling rejection of pancreas allografts in man it would offer unstable diabetics in renal failure a more hopeful outlook than conventional immunosuppression.

Animals↗
PubMed1979

Enzyme immunoassay of carbamazepine with a centrifugal analyzer.

We describe a rapid enzyme immunoassay for carbamazepine with a centrifugal analyzer (Rotochem IIA-36). Reagent costs are reduced fourfold while good precision and sensitivity are maintained. Sample volume is 10 microliter, and as many as 28 patients' sera can be measured during an assay time of 225 s. Assay temperature is 30 degrees C, the wavelength 340 nn. Linearity is excellent for a carbamazepine concentration range of 1 to 12 mg/L; analytical recovery is quantitative. Results correlate well with those by liquid- and gas-liquid chromatography. Absorbance rates for each carbamazepine concentration are acquired by a multi-point kinetic rate program and a computer program provides a logit-log transformation of absorbance rate vs. concentration data for final calculations in the assay. Hemoglobin interference precludes analysis of severely hemolyzed specimens.

Carbamazepine↗
PubMed1979

Performance assessment of the GammafloTM automated radioimmunoassay system by assaying for digoxin.

We report an evaluation of the GammafloTM automated continuous-flow radioimmunoassay instrument in which we used a digoxin assay to assess system performance. System operation was based on combined continuous-flow and column-chromatographic techniques. No drift or carryover was detectable in 180 within-assay consecutive determinations performed at a rate of 42 determinations per hour (5 h of continuous operation). Within-assay and between-assay precision were less than 6% (coefficient of variation). The automated method correlated well (r = 0.960 and 0.952, respectively) with two established manual digoxin radioimmunoassay procedures. The data suggest this automated system offers a valid alternative to manual radioimmunoassay procedures in terms of overall precision, simplicity of operation, and sample throughout capacity.

Autoanalysis↗
PubMed1979

Centrifugal analyzer method for total bilirubin in serum by use of diazotized 2-chloroaniline-5-sulfonic acid.

We describe two centrifugal analyzer methods for measuring total bilirubin in serum. Diazotized 2-chloroaniline-5-sulfonic acid is used in both. In the first procedure, ethylene glycol and methanol are used as an accelerator solvent; results correlate well with those by a Jendrassik and Grof method adapted to the centrifugal analyzer, but there is considerable hemolysis interference. In the second method, dimethyl sulfoxide is used with the ethylene glycol/methanol solvent and almost all hemolysis interference is eliminated. For either method, a 15-microliter sample is required. In the second method, instrument response is linearly related to concentration to 250 mg/L and the within-run precision (CV) is about 1%.

Azo Compounds↗
PubMed1978

Self-association of hemoglobin betaSH chains is linked to oxygenation.

Self-association of unliganded beta(SH) chains into tetramers (4 beta(1) [unk] beta(4)) is experimentally found to be energetically less favorable (DeltaG(0) = -19.05 +/- 0.30 kcal) than the corresponding oligomerization of fully oxygenated chains (4 beta(1)X [unk] beta(4)X(4); DeltaG(0) = -22.45 +/- 0.35 kcal). Hence the tetramers must bind oxygen with a higher affinity than that of dissociated chains. Calculations are presented showing why this affinity difference is not easily detected. The linkage is in a direction opposite to that exhibited by normal hemoglobin A, in which oligomerization of high-affinity unliganded dimers (2 alphabeta [unk] alpha(2)beta(2)) leads to tetramers with decreased oxygen affinity. In contrast, the oligomerization of high-affinity, unliganded beta(SH) chains leads to tetramers with even higher affinity. The results imply the existence of at least two conformational states for beta chains. Effects of inositol hexaphosphate on beta chain association were investigated. Inositol hexaphosphate was found to have no measurable effect at pH 7.4, in contrast to pH 7 where very pronounced effects have been observed. Some theoretical aspects of the linkages are presented and the relationship of the findings to concepts of structural transition and allosteric regulation is discussed. In contrast to the beta chains, self-association of alpha chains into dimers was found to occur with the same free energy in both unliganded and fully oxygenated states. Thus, the self-association of alpha chains is not linked to oxygenation.

Hemoglobin A↗
PubMed1978

Reciprocal effects in human hemoglobin: direct measurement of the dimer-tetramer association constant at partial oxygen saturation.

An equilibrium gel permeation technique has been developed for determining as a function of oxygenation state the equilibrium constants for association of hemoglobin subunits. By using this method, the dimer-tetramer constant for human hemoglobin at a partial oxygenation state corresponding to 20% saturation for tetramers has been determined as 3.7 X 10(6) M-1 (dimers). Under the same conditions the corresponding constant for fully oxygenated hemoglobin is 4.1 X 10(5) M-1. These results are found to be in good agreement with the predicted behavior of the association reaction based upon oxygen binding curves measured as a function of protein concentration. Thus a high degree of consistency is found between the two independent experimental approaches to the reciprocal effects of this linkage system, lending support to the theory proposed earlier for these phenomena.

Hemoglobins↗
PubMed1977

Thermodynamic studies on subunit assembly in human hemoglobin. Self-association of oxygenated chains (alphaSH and betaSH): determination of stoichiometries and equilibrium constants as a function of temperature.

The homogeneous self-association of isolated alphaSH chains and betaSH chains from human hemoglobin has been studied by analytical molecular sieve chromatography over the concentration range 0.004 to 15.2 mg/ml. Detailed studies were carried out as a function of temperature at pH 7.4 in 0.1 M Tris/HCl, 0.1 M NaCl, 1 mM Na2EDTA in order to establish stoichiometries, equilibrium constants, and enthalpies for the self-association reactions. The dissociation data best describe the alphaSH system as being a monomer-dimer equilibrium (2alpha1 in equilibrium alpha2). Under the same conditions the betaSH system is best described by a monomer-tetramer equilibrium (4beta1 in equilibrium beta4). van't Hoff enthalpies were determined from the temperature dependence of the equilibrium constants. For the 2alpha in equilibrium alpha2 reaction the molar enthalpy delta H = 4.3 +/- 0.5 kcal, and for the reaction 4beta1 in equilibrium beta4, deltaH = 23.5 +/- 1.0 kcal. Unitary entropies were determined to be: deltaSu = 40.6 e.u., deltaSu = 177.5 e.u., respectively. Thermodynamic parameters for association of the two types of chains are roughly comparable in magnitude if four bonding interactions are assumed in the beta4 tetramer. Both reactions are entropy-driven, and the overall results (including salt effects) are consistent with a dominant role of hydrophobic interactions. Increasing the NaCl concentration to 2 M at 21.5 degrees under the same buffer conditions increases the association constant for both the alphaSH and betatsh chains. This increase in the association constants with increasing salt concentration is attributable to the increased binding of salt, or the release of bound water upon formation of the association complexes, or both. The present results do not distinguish between these possibilities. The introduction of inositol hexaphosphate (IHP) was found to have no effect upon subunit association in betaSH chains. This result and the previously observed effect of IHP upon oxygenation of beta chains imply that oxygenation and self-association are completely unlinked in this system. Accurate determinations of (a) the enthalpy changes for homogeneous reactions of isolated chains, carried out in this study and of (b) the enthalpy of forming alpha2beta2 tetramers from alphabeta dimers provide a basis for the interpretation of (c) calorimetric studies on reconstitution of hemoglobin from the isolated chains, described in accompanying papers.

Heme↗
PubMed1977

Thermodynamic studies on subunit assembly in human hemoglobin. Calorimetric measurements on the reconstitution of oxyhemoglobin from isolated chains.

Calorimetric heats generated upon mixing solutions of alphaSH and betaSH chains of human hemoglobin have been studied by isothermal heatburst microcalorimetry as a function of mixture composition. Based upon studies described in accompanying papers, the contributions to the measured heats arising from (a) alpha chain self-association, (b) beta chain self-association, (c) association of dimers to form tetramers, have been evaluated. Taking these processes into account, the calorimetric data have been used to determine the enthalpy of formation for alphabeta dimers, yielding a value of -15.71 +/- 0.96 kcal in the fully oxygenated state at 21.5 degrees in 0.1 M Tris/HCl, 0.1 M NaCl, 1 mM Na2EDTA, pH 7.4. The total enthalpy for assembly of a mole of hemoglobin tetramers from oxygenated chains is -27.6 +/- 2.1 kcal. Combining results of this study with independently determined information, limits can be placed upon the magnitude of the enthalpy for dimer formation in unliganded hemoglobin. The total enthalpy for assembly of a mole of unliganded hemoglobin tetramers from unliganded chains is -61.6 +/- 3.5 kcal, or approximately twice the value for oxygenated hemoglobin. This difference lies entirely in the dimer-tetramer stage of assembly. There are essentially no oxygenation-linked thermodynamic quantities (deltaG, deltaH, deltaS) associated with alphabeta dimer formation from isolated chains.

Calorimetry↗