Immunochemical Studies with Lysine Vasopressin

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Abstract
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 radio-immunoassay method. Precipitating antibodies reacting with albumin and various conjugates were also found. LVP was iodinated with I131 or I125 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-I131 and antiserum alone. LVP-i131 bound to antibody was detected and separated from free LVP-I131 by precipitation of the antibody bound LVP-I131 with goat anti-rabbit gamma globulin serum. This reaction could be inhibited competitively by un-labeled LVP so that as little as 15 [mu][mu]g (4 [mu]U) 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-I131 immunoprecipitation compared to unlabeled LVP. In contrast, 4000 times more oxytocin was required to equally inhibit this reaction. Various albumin preparations were not inhibitory.

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