A method of estimating histamine in plasma.

The method is intended for the estimation of minute quantities of histamine in blood plasma. A neutralized trichloracetic acid extract of plasma is adsorbed at pH 8 on a column prepared by mixing a quantity of the cationic exchange resin Amberlite XE-64 with powdered cellulose as a supporting medium. Histamine is adsorbed but N-acetylhistamine is not: the amines can therefore be estimated independently. Elution of the histamine is by displacement with HCl. The eluate is converted into the solution for bioassay on the superfused guinea-pig ileum.In recovery experiments histamine was added in the range 25 to 100 ng. to solutions of known composition and to plasma (5 ml.) obtained from man and the cat. The mean recovery in this range for histamine added to plasma was 82.5%+/-2 S.E. (17 estimations).The histamine equivalent of human plasma obtained from the antecubital vein was found to be less than 1 ng./ml.It was possible by this method to follow the concentration of histamine in the arterial plasma of the cat when histamine was infused intravenously at a rate of 330 ng./kg./min. There was no perceptible change in the arterial blood pressure during the infusion, but the plasma histamine rose from <0.3 ng./ml. to 3.4 ng./ml. (mean of 2 estimations).