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Lysine vasopressin (LVP) has been coupled to bovine serum albumin by 2 techniques. One method employed toluene-2,4-diisocyanate and the other a carbodiimide. LVP conjugates of both types proved to be potent antigens and specific antibody to LVP was obtained by immunization of rabbits with each type of conjugate. The LVP specific antibody was demonstrated by a radioimmunoassay method. Precipitating antibodies reacting with albumin and various conjugates were also found. LVP was iodinated with 131I or 125I and preparations of high specific activity were obtained. Up to 90% of the radioactivity was immunologically reactive. No precipitation was observed with LVP or LVP-131I and antiserum alone. LVP-131I bound to antibody was detected and separated from free LVP-131I by precipitation of the antibody bound LVP-131I with goat anti-rabbit gamma globulin serum. This reaction could be inhibited competitively by unlabeled LVP so that as little as 15 μMg (4 μU) unlabeled hormone was detected. In inhibition studies 1.4 times as much arginine vasopressin and 3.3 times as much phenylalanine- 2-lysine vasopressin were required to inhibit LVP-13lI immunoprecipitation compared to unlabeled LVP. In contrast, 4000 times more oxytocin was required to equally inhibit this reaction. Various albumin preparations were not inhibitory. (Endocrinology78: 809, 1966)
Permutt et al. (Fri,) studied this question.