A COMPARATIVE STUDY ON BIOASSAY AND RADIOIMMUNOASSAY OF VASOPRESSIN IN HUMAN URINE

Abstract

The excretion of vasopressin in urine from healthy human subjects under different stages of hydration was estimated in urine extracts by bioassay (rat antidiuresis) and radioimmunoassay [RIA]. In normally hydrated subjects the excretion was 490 .+-. 164 .mu.U[microunits]/h and 430 .+-. 133 .mu.U/h for bioassay and RIA, respectively, (mean .+-. SEM [standard error of the mean], n = 5). After total fluid restriction for 10-12 h the excretion increased to 1370 .+-. 329 .mu.U/h for bioassay and 1163 .+-. 279 .mu.U/h for RIA (mean .+-. SEM, n = 6). An oral water load (25 ml/kg) reduced the value to 169 .mu.U/h (bioassay) and 118 .mu.U/h (RIA) (mean, n = 2). In general the biological estimations were 20% higher than the immunological estimations (P < 0.01). The urinary vasopressin excretion was positively correlated to urine osmolality. Synthetic arginine vasopressin (AVP) and urine extracts were both heterogeneous in ion exchange chromatography. The immunoreactive material was always eluted in 2 peaks, situated at the same places in the elution diagram. The material in the 2nd peak was biologically active. The 1st peak from the AVP standard was biologically inactive, whereas the same peak from urine extract was active. This peak was an artefact formed during the extraction procedure.