Abstract
Publisher Summary This chapter discusses determination of tissue histamine by an enzymatic isotopic assay. The method depends on the enzymatic transfer of the methyl-14C of S-adenosylmethionine-14C (AMe-14C) to tissue histamine to form methylhistamine-14C. A tracer amount of histamine-all is added to endogenous histamine; the percent of the tritium in the methylhistamine formed indicates the extent of the enzymatic methylation. The final product formed is methylhistamine-14C-3H. Endogenous AMe is destroyed by heating so that there is no dilution of the added 14C-AMe-14C. The enzyme histamine methyl transferase used for the reaction is highly specific for histamine. The only tissue component that is methylated in the reaction is histamine; chloroform extraction separates histamine from methylhistamine. Thus the ratio 14C: 3H is linearly related to the tissue content of histamine. With each assay are included standard determinations of two concentrations of authentic histamine as well as histamine added to tissue homogenates before heating. Histamine added to tissues is recovered to the extent of 90-100%.
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