Accuracy of Single Concentration Estimations of Platelet Angiotensin II Receptor Number

Abstract

Platelet angiotensin II (AngII) receptor number has been suggested as a screening test for pregnancy-induced hypertension. However, markedly different false-positive rates have been reported, perhaps the result of differing methods used. We sought therefore to compare the two methods. Platelet AngII receptor number was determined by saturation analysis with computerized curve fitting and specific binding at a single radioligand concentration. The two methods were compared by correlation and by plotting their differences v their means, to determine their limits of agreement. There were significant correlations between the value obtained by saturation analysis and each of the three single ligand concentrations studied (1 nmol/L, P < .001; 500 pmol/L, P < .001; and 250 pmol/L, P < .01). However, for none of the three did the regression line approach the line of equality. Assessment of agreement by comparing differences and means for each subject showed increasing scatter with increasing receptor number and 95% confidence intervals too large to be clinically relevant. We conclude that the receptor number estimated from specific binding at one ligand concentration differs significantly from that obtained by saturation analysis. The limits of agreement of the two methods are wide and we urge caution in the use of single ligand concentration methods for estimating binding site densities.

Effects of nitric oxide synthase inhibition on angiotensin receptors and metabolism in the pregnant hypertensive rat

“…Further purification was performed by gradient reverse-phase HPLC using a C-18 Selectosil column (Phenomenex, Torrance, CA, U.S.A.) as described previously [24]. Further purification was performed by gradient reverse-phase HPLC using a C-18 Selectosil column (Phenomenex, Torrance, CA, U.S.A.) as described previously [24].…”

“…Samples were reconstituted with barbitone buffer and assayed by RIA as described previously [24]. After centrifugation at 180 g for 10 min (4 mC), the plasma was applied to and extracted on a Sep-Pak C-18 cartridge using 2 ml of acetonitrile\distilled water\acetic acid (74 : 24 : 4, by vol.).…”

Effects of nitric oxide synthase inhibition on angiotensin receptors and metabolism in the pregnant hypertensive rat

“…Further purification was performed by gradient reverse-phase HPLC using a C-18 Selectosil column (Phenomenex, Torrance, CA, U.S.A.) as described previously [24]. The specific radioactivity of the ligand was determined at 2-week intervals by selfdisplacement in an RIA [24].…”

“…Specimens were then blown down to dryness under nitrogen and stored at k20 mC until assay. Samples were reconstituted with barbitone buffer and assayed by RIA as described previously [24]. The polyclonal antibody used in this assay cross-reacts with ANG III, but has negligible cross-reactivity with ANG I under assay conditions.…”