A highly sensitive and rapid radioimmunoassay for the determination of arginine8-vasopressin

A highly sensitive radioimmunossay for arginine8-vasopressin
(argipressin; INN) measurement was developed using Amberlite XAD 2
resin columns to extract arginine8-vasopressin from acidified human
plasma. Arginine8-vasopressin was determined by a rapid
radioimmunoassay method (2 x 20 h) using a specific antibody and
125I-labelled antigen. The bound fraction was separated by
adsorption of the free fraction onto bovine serum albumin-coated
charcoal; this resulted in low unspecific binding of less than 2%.
Recovery experiments in the physiological range resulted in a mean
(+/- SEM) recovery of 88 +/- 3%. The radioimmunoassay consistently
yielded a detection limit of 0.3 ng/l (ED90) and a mean 50% binding
intercept (ED50) of 3.5 ng/l. Arginine8-vasopressin
immunoreactivity was characterized by reverse-phase high
performance liquid chromatography, which confirmed the specificity
of the assay. Serial plasma dilution curves paralleled the standard
curve. The intra- and inter-assay variations were 9.4% and 15%,
respectively. Arginine8-vasopressin concentrations in healthy
subjects were determined in normal hydration status (2.2 +/- 0.3
ng/l; n = 11), as well as during suppression by water immersion
(1.5 +/- 0.2 ng/l; n = 11) or by water loading (1.6 +/- 0.2 ng/l; n
= 8). Thus, this assay allows for a sensitive, accurate and rapid
quantification of plasma arginine8-vasopressin concentrations.