Radio-enzymatic determination of histamine: Interference by fluoride and possible activation of histamine methyl transferase

The reproducibility of a radio-enzymatic method for determining plasma histamine was found to be affected by the anti-coagulant used for collecting blood. Recovery experiments from whole blood indicated that heparin yielded values that were more accurate than with EDTA or sodium fluoride; fluoride gave a mean value which was + 41% higher than with heparin (P = 0.054). Addition of fluoride to a standard calibration curve, and of increasing amounts to aliquots of 5 ng histamine also yielded higher values than in controls, up to + 15% (P < 0.1) and + 14.1% (P = 0.03) respectively. Fluoride did not affect the detecting system and was not contaminated with histamine; nor did it breakdown the methyl donor, S-adenosyl-L-methionine. It is concluded that heparin is the anti-coagulant of choice and that fluoride may activate histamine methyl transferase from pig brain. Fluoride may possibly have a biological role as an enzyme-activator and a usefulness in the therapy of mastocytosis. (C) 1998 Elsevier Science B.V. All rights reserved.