Radioimmunoassay For Plasma Aldosterone Research Articles

Highly sensitive and rapid radioimmunoassay for aldosterone in plasma and cell culture medium

A radioimmunoassay for aldosterone was developed using a sensitive and specific antibody and 125Iodinated-aldosterone. This assay could be used for direct determination of aldosterone in cell culture medium or after extraction of aldosterone from plasma by solid phase procedure using C18 Sep-pak cartridges. The very low cross-reactivity of the antibody with cortisol and corticosterone (0.005% and 0.04% respectively) would allow the direct determination of aldosterone in cell culture medium without any prior extraction step. Since the incubation is performed at room temperature for 1 h and then, at 4 degrees C for 15 min, the results can be obtained in less than 3 h. The assay was linear from 0.5 fmol/tube to 1500 fmol/tube with an ED50 at 30 fmol/tube. The accuracy of the assay estimated using spiked plasma samples with a known amount of aldosterone give a coefficient of correlation of 0.97 (n = 10) between the aldosterone concentrations found and expected levels. The within-assay variability for plasma aldosterone varied from 4.7 to 11.1% and the between-assay variability ranged from 13.9 to 14.2%. The coefficient of correlation between plasma aldosterone measured by this new assay or by a current assay was 0.8 (n = 43). In summary, the combination of a shortened incubation time with a simple solid phase extraction for aldosterone in serum samples represents the major advantage of the present assay over the current methodology which usually requires a chromatographic separation of the mineralocorticoid prior to radioimmunoassay. Therefore this assay would be useful in experimental studies as well as in clinical laboratory.

Evaluation of an aldosterone radioimmunoassay: the renin-angiotensin-aldosterone axis as a function of sex and age.

A highly specific radioimmunoassay for aldosterone in plasma has been developed utilising extraction from plasma into dichloromethane, an antiserum raised to aldosterone-3-carboxy-methyloxime-BSA and a radio-iodinated derivative of aldosterone. The plasma values obtained after only extraction correlated very well with the results following chromatography over celite. The within- and between-batch variations for plasma pools ranged between 5 and 15%. The range obtained, 100-1806 pmol/L for 96 random upright subjects, was comparable to others reported. Measurement of plasma aldosterone and plasma renin activity in these subjects showed that both these parameters are higher in subjects under 40 years of age than in those over 40. In addition, plasma aldosterone levels are higher in women than in men even though their plasma renin activity levels are similar. The plasma aldosterone/renin activity ratios which provide an index of adrenal sensitivity to stimulation, are lower in men than in women. The findings in this study suggest that higher aldosterone levels in younger subjects are associated with greater stimulation of the adrenals than in older subjects and that the adrenal is more sensitive in women than in men.

Radioimmunoassay of plasma aldosterone by chromatography on Sephadex LH 20

The use of Sephadex LH 20 is described for the estimation of plasma aldosterone. Due to this chromatography column, blanks of the estimation are very low and recoveries very good. The high specificity of the determination is obtained with the use of an antibody anti-aldosterone, showing very low cross reactions with other steroids such as corticosterone, cortisone and cortisol. Normal values in humans, with an average value of 3.80 ng/100 ml, are in good agreement with those found in the literature.

A simplified radioimmunoassay for plasma aldosterone employing an antibody of unique specificity

A highly selective antibody for aldosterone, produced as indicated in the companion paper, was utilized as the basis for a radioimmunoassay for aldosterone in plasma which did not require fractionation of this compound from other steroids. No appreciable crossreactivity was found with any steroid tested except 18-hydroxy-11 deoxycorticosterone and 18-OH-corticosterone, but the affinity for these compounds was four orders of magnitude lower than for aldosterone. Specificity was further documented by demonstrating undetectable aldosterone levels in adrenalectomized dogs and supression of measured aldosterone levels to 0 in a dog subjected to Na loading and a course of deoxycorticosterone. Immunologic identity of standards and plasma aldosterone was demonstrated by showing that dilutions of a human plasma containing a high concentration of aldosterone paralleled a standard curve. Sensitivity, recovery, and accuracy of the method were tested and found satisfactory. Good correlation of results with a method employing chromatographic isolation of aldosterone was demonstrated. Aldosterone plasma values in normal human subjects in response to changes in posture and Na intake, as measured by this method, correlated in the expected fashion with changes in renin activity but did not correlate with plasma cortisol, which followed the anticipated diurnal cycle.

A simplified radioimmunoassay of plasma aldosterone.

ABSTRACT Radioimmunoassay of plasma aldosterone has been simplified by the elimination of the chromatographic purification step. A neutral plasma extract is subjected to water/toluene partition and oxidation with periodic acid and the neutral etiolactone product assayed with an aldosterone antiserum which cross-reacts with the etiolactone. Aldosterone concentrations in human plasma determined by this procedure agree with values obtained by other methods.

A radioimmunoassay for plasma aldosterone without chromatography.

A radioimmunoassay for plasma aldosterone has been developed which requires no preliminary chromatography. Purification consists of partitioning between cyclohexane and water, and periodate oxidation followed by a sodium hydroxide wash. The antibody affinity for aldosterone-γ-lactone was approximately 5 orders greater than for other interfering steroids. The specificity of the method was confirmed by the finding that additional purification by Sephadex column chromatography did not lower the observed values. Accuracy was confirmed by recovery studies from pooled plasma containing 70.6 pg/ml (recovery = 0.964 added + 74.9 ± 16.3 pg/ml in the range of 0 to 300 pg/ml added). The coefficient of variation for samples assayed on 5–7 different occasions was 10.6 to 14.1%. This assay is a rapid, efficient and accurate means for measuring plasma aldosterone.

Radioimmunoassay of plasma aldosterone and its clinical application

Radioimmunoassay of plasma aldosterone and its clinical application