PubMed · 1437103
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G Bíró, M Antal. 1992-10-18. [Cholesterol intake].. https://pubmed.ncbi.nlm.nih.gov/1437103/
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We have developed a high-performance liquid chromatography (HPLC) method for measurement of cholesterol in the major classes of serum lipoproteins, i.e., HDL, LDL, IDL, VLDL, and chylomicrons. Lipoproteins in serum were separated on a column containing diethylaminoethyl-ligand nonporous polymer-based gel by elution with a step gradient of sodium perchlorate concentration, and detected by post-column reaction with a reagent containing cholesterol esterase and cholesterol oxidase. The within-day assay and between-day assay coefficients of variation for cholesterol concentration in lipoproteins were in the ranges of 0.9-6.4% and 1.1-11.9%, respectively. The correlation coefficients between the values of HDL, LDL, IDL, VLDL, and chylomicron cholesterol measured by the HPLC method and those estimated by an ultracentrifugation method were 0.892, 0.921, 0.840, 0.930, and 0.873, respectively. Values of remnant-like particle cholesterol measured by an immunoseparation technique (Japan Immunoresearch Laboratories, Japan) were significantly correlated with VLDL and chylomicron cholesterol values measured by the HPLC method (r = 0.883 and r = 0.729, respectively). This rapid and accurate HPLC method was successfully applied to the analysis of plasma lipoproteins of patients with hyperlipidemia.
We propose here a simple scheme to use information on compliance and prerandomization covariates to improve analysis of randomized trials with non-compliance. We use the data to determine the effect of randomization on treatment received among various strata defined by pretreatment covariates. When the effect of treatment received on the outcome of interest is the same across strata and pretreatment covariates predict non-compliance, weighting the estimating functions by the effect of randomization on treatment received can improve the precision of explanatory estimates of treatment effect and can increase the power of intent-to-treat tests of the null hypothesis. Efficiency gains under the weighting scheme are a simple increasing function of the variability of these weights. Such weighting schemes will often lead to improvements even when these conditions are not met. We use a randomized trial of cholestyramine to illustrate these points.
The binding of copper(II) ions to membrane-bound synthetic receptors has been investigated. Complexation fitted a 4:1 receptor:copper(II) model, and the observed binding constants are significantly enhanced at the membrane relative to solution; these effects can be explained by the lower polarity of the membrane-water interface and the concentrating effect of the membrane, with no observed contribution from receptor preorganization. The stoichiometry of the complex formed is very sensitive to the concentration of the receptor in the membrane, and at low concentrations, binding is reduced relative to solution controls. This implies that by increasing or decreasing the number of receptors in their membranes, cells can finely tune biological responses such as chemotaxis that depend on the size of the receptor-ligand clusters formed.