Radioimmunoassay of Arginine Vasopressin in Urine: Development and Application*

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Abstract
A sensitive and specific RIA system for measurement of urinary arginine vasopressin (AVP) was developed. RIA sensitivity was 0.4 μU/ml (∼0.8 pg/ml). Urine samples were extracted using columns of octadecasilyl-silica. The mean (±sem) recovery of AVP after extraction (77.7 ± 1.4%) was independent of urinary osmolality. The extracted immunologically active material migrated similarly to synthetic AVP on high pressure liquid chromatography. AVP immunoreactivity was found to be stable in urine stored for 24 h at room temperature and stable for 3 months when acidified promptly and stored at −20 C. Using the RIA system, we measured urinary AVP excretion as a percentage of total body AVP clearance. For this study, AVP (3.7 μU/min·kg) was infused iv into four healthy nonsmoking adults in whom endogenous AVP was suppressed by oral water loading. The mean urinary AVP excretion rate was 14.7 ± 2.1%. There was a highly significant positive correlation between log urinary AVP concentration and urinary osmolality (r = 0.97).