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

Abstract

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. In normally hydrated subjects the excretion was 490 ± 164 μU/h and 430 ± 133 μU/h for bioassay and radioimmunoassay respectively (mean ± sem, n = 5). After total fluid restriction for 10 to 12 h the excretion increased to 1370 ± 329 μU/h for bioassay and 1163 ± 279 μU/h for radioimmunoassay (mean ± sem, n = 6). An oral water load (25 ml/kg) reduced the value to 169 μU/h (bioassay) and 118 μU/h (radioimmunoassay) (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 second peak was biologically active. The first peak from the AVP standard was biologically inactive, whereas the same peak from urine extract was active. This peak was shown to be an artefact formed during the extraction procedure.