[Development of radioimmunoassay for plasma arginine vasopressin and its application to the diagnosis of children with central diabetes insipidus].

For measurement of plasma arginine vasopressin (AVP) in children with central diabetes insipidus (DI), a sensitive and specific radioimmunoassay (RIA) for AVP was developed. The anti AVP serum used in this assay bound 50 percent of an purified 125-I-labeled-AVP (125I-AVP) at a final dilution of 5 X 10(4) and its cross reaction with lysine vasopressin, 1-deamino-8-D-arginine vasopressin and oxytocin were 7, 15, and 0%, respectively. Column chromatography of Sephadex G-25 superfine was used for purification of 125I-AVP and four major peaks of radioactivity were observed. The purified 125I-AVP was found in 3rd peak by the highest binding activity with the anti-AVP serum. On the other hand, extraction of AVP from plasma was carried out by the acetone extraction procedure and as little as 1.2 pg per milliliter of AVP in plasma was detected in this RIA. In dehydration state plasma concentration of AVP was 4.5 +/- 1.1 pg/ml (mean +/- SE) in normal seven children (control), 1.5 +/- 0.2 pg/ml in six patients with complete DI and 3.4 +/- 0.6 pg/ml in five patients with partial DI diagnosed with Miller test (complete DI vs partial DI; p less than 0.02, partial DI vs control; no significant). The evaluation of diagnostic value of AVP level measured with RIA in complete DI and partial DI diagnosed with Miller test based on urine osmolality was discussed.