Development of a Sensitive Radioassay of Histamine for In vitro Allergy Testing

Abstract

A radioenzymatic assay for the measurement of histamine is described, based on the incubation of histamine in the presence of histamine-N-methyl-transferase from rat kidney and [³H-methyl]-S-adenosyl-L-methionine (sp act 15 Ci/mmol) in phosphate buffer, 0.05 mole/I, pH 7.9, at 37°C for 60 min. The N-[³H]-methyl]histamine generated was selectively extracted into toluene/isoamyl alcohol (3:2) and the quantity of the tritium in the sample was determined by liquid-scintillation counting. As little as 1 nmol/I of histamine can be detected. The assay is specific, with no cross-reactivity noted for several compounds closely related to histamine. The assay was used to measure the released histamine of a group of allergic subjects following the incubation of their blood with various allergens. A good correlation was found between histamine release from whole blood and the response of skin mast cells to intradermal antigen administration.