A direct, sensitive microassay for mammalian histidine decarboxylase

A microassay procedure for mammalian histidine decarboxylase based on the conversion of l-[ 3H]histidine to [ 3H]histamine, which were separated by an alkaline butanol extraction followed by thin-layer chromatography, is described. This assay is direct and simple to perform, in addition to being very sensitive and reproducible. It is useful for tissues containing high levels of endogenous histamine, because only newly formed radiolabeled histamine is measured. This report includes information on histidine decarboxylase activity at various pH levels, in different buffers, and in the presence of selected histamine active drugs. In addition, it describes histidine decarboxylase activity in several fetal rat tissues.