The Specificity of Antisera for the Radioimmunoassay of Arginine-Vasopressin in Human Plasma and Urine during Water Loading and Dehydration

Abstract

1. Rabbit antisera against arginine-vasopressin (AVP) were evaluated for sensitivity and specificity in a radioimmunoassay based on the extraction of AVP from plasma and urine on to Florisil. 2. Comparison of the immunoreactivity of AVP with analogues showed that one antiserum (R2) reacted principally with the hexapeptide ring and another (R4) bound to the tripeptide tail and was reactive with some reduction and hydrolytic products of the native peptide. 3. The minimum amount of AVP measurable in the radioimmunoassay was 1 pg. The extraction of AVP from plasma and urine gave a recovery of 93 per cent (sd 5 per cent). A plasma sample repeatedly assayed with R2 gave a value of 1.4 ng/1 (sd 0.2, n=12). 4. The antiserum specific for the hexapeptide ring (R2) showed that in normal subjects AVP concentration ranged from 3.2 +/- 2.52 ng/1 after dehydration to 0.16 +/- 0.1 ng/1 after water loading.

Effects of drugs on water metabolism.

“…In five normal subjects mean plasma osmolality fell from 276 mmol (mosmol)/kg to 263 mmol (mosmol)/ kg and mean plasma AVP fell from 0.57 to 0.16 ng/l (Thomas & Lee, 1976 Insulin-induced hypoglycaemia caused a three fold rise in plasma AVP 30 min after the injection. This non-osmotic stumulus appears to be a potent stimulus to AVP secretion.…”

“…Essentially the hexapeptide ring is overlaid by the tripeptide tail (Figures 1 and 2). Thomas & Lee (1976) were able to raise two classes of antibody by injecting vasopressin into rabbits. These two classes of antibody were known as the R2 type and the R4 type.…”

“…Figure 2 The three dimensional structure of arginine vasopressin together with the points of interaction with R2 type and R4 type antibodies. (After Thomas & Lee, 1976).…”

“…In the studies by Monson & Richards (1978) Miller & Moses (1969) had previously developed a method suitable for urine but not sensi-tive enough to measure plasma levels. Since these pioneer observations several other groups have developed sensitive and specific radioimmunoassays capable of measuring AVP in both small volumes of urine and of plasma (Thomas & Lee, 1976). The problems which remain are concerned with non specific interference and the disparity between biological and immunological activity.…”

“…These may be separated from AVP by adsorption of the latter on Florisil (100-200 mesh). The peptide is then eluted with acidified aqueous acetone (Thomas & Lee, 1976). Figure 2 The three dimensional structure of arginine vasopressin together with the points of interaction with R2 type and R4 type antibodies.…”