Radioimmunoassay of (8-arginine)-vasopressin. I. Methodology.

A radioimmunological method for the determination of the human antidiuretic hormone [8-arginine]-vasopressin (AVP), is described in detail. The antiserum has been raised in rabbits injected with AVP adsorbed onto charcoal particles and is used at a final dilution of 1:200,000. It contains antibodies directed specifically against the C-terminal tripeptide and possesses a high association constant of 8.2 x 10(12) 1/mole. AVP is labelled in monoiodinated form (as proven after pronase digestion) at a high specific activity close to the theoretical maximum after purification from unlabelled hormone on Sephadex gel. The standard curves are characterized by a Bo of 55%, a limit of detection ascertained at least at 3 pg (10% displacement) and a 50% displacement achieved with 35.5 pg. The index of precision lambda ranges from 0.033 to 0.042. The conditions of the assay (buffer's composition and pH, timing) were systematically varied and tested. In addition the result of immunization of chicken with AVP is reported. The assay is adequate for the measurement of AVP in urine and plasma and will be described in forthcoming papers.