A Simple and Highly Sensitive Radioimmunoassay for 8-A : rginine Vasopressin in Human Plasma Using a Reversed-Phase C<SUB>18</SUB> Silica Column

A highly sensitive and simple radioimmunoassay for the measurement of 8-arginine vasopressin (AVP) in human plasma has been developed. The dose response curve ranges from 0.025 to 8 pg/tube. This simple extraction technique employing an ODS C18 column recovered 87.1 +/- 10.4 (mean +/- SD)% of AVP in the range of 1-10 pg/ml added to 0.5 ml plasma. Determination of AVP in each fraction of plasma, which was gel-filtrated through a Sephadex G25 (1 X 25 cm), revealed that the fraction of plasma AVP was superimposed on that of authentic AVP, and interference of non-specific substances was completely eliminated by an ODS C18 column. Using the assay, 13 of 16 patients with diabetes insipidus (DI) showed plasma AVP concentrations ranging from 0.03 to 0.21 pg/ml, and the other 3 patients had less than 0.03 pg/ml. The AVP concentrations of DI were clearly distinguished from those obtained in normal subjects (0.30-4.20 pg/ml, n = 65). The within and between assay variability was about 10% each. Plasma AVP concentrations (mean +/- SD) of normal subjects (n = 6) standing, sitting, and supine after an overnight of fluid deprivation were 2.41 +/- 1.15, 1.95 +/- 0.85 and 0.97 +/- 0.48 pg/ml (30 min after) respectively. Plasma AVP concentrations of normal subjects (n = 6) after water load (20 ml/kg wt) were clearly reduced from 1.89 +/- 1.00 (before) to 0.42 +/- 0.21 (standing for 60 min) and also from 0.89 +/- 0.41 to 0.40 +/- 0.22 pg/ml (supine for 60 min).