Simultaneous radioimmunoassay for plasma arginine-vasopressin and oxytocin using DEAE Sephadex A 25 extraction

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Abstract
A sensitive and specific radioimmunoassay method for simultaneous measurement of plasma arginine vasopressin (AVP) and oxytocin (OT) has been developed utilizing an extraction technique on DEAE Sephadex A 25. This procedure resulted in mean recoveries of 70.7% (AVP) and 65.4% (OT) in the peptide range of 5 to 100 pg/4 ml. The sensitivity of the assay is 0.5 pg/tube for AVP and 2 pg/tube for OT. The lower limit of detection for plasma extracts was 1.2 pg AVP/ml and 5 pg OT/ml plasma. Employing this method in normal human non smokers and ad libitum fluid the basal levels (mean ± SE) of plasma AVP are 3.5 ± 0.2 pg/ml in males and 4.6 ± 0.4 pg/ml in females and the basal concentrations of plasma OT are 5.1 ± 0.3 pg/ml in males and 5.4 ± 0.3 pg/ml in females. Dehydration and water loading produced significant changes in plasma AVP and OT concentrations and a significant correlation exists between plasma AVP and plasma (r= 0.96, p < 0.001 ) and urinary (r = 0.84, p < 0.01 ) osmolality, but not between plasma OT concentrations and plasma (r =0.11, NS) and urinary (r = 0.27, NS) osmolality. These results suggest that a wide range of physiological and pathophysiological changes in plasma AVP and OT can be simultaneously measured by the extraction procedure and the radioimmunoassay described.