Degradation of histamine by homogenized human skin in vitro, in the presence of the cofactor S-adenosyl methionine, indicates the presence of the histamine metabolizing enzyme histamine-N-methyl transferase in human skin. Under the experimental conditions described, no significant histamine degradation by diamine oxidase was observed. 2. The enzyme activity is temperature-sensitive with an optimum at 37 degrees C. The enzyme is stable in in intact excised skin at -20 degrees C, but unstable in homogenized skin at this temperature. 3. Little or no enzyme activity is present in mid- or deep dermis, but the distribution of the enzyme between superficial papillary dermis and epidermis is uncertain. 4. The presence of a potent histamine degrading mechanism raises the possibility that histamine-N-methyl transferase activity may be an important modulating factor in histamine-mediated skin disorders.
