Biogenic amines in the Arthus reaction.

The concentrations of serotonin, tryptamine, dopamine, and tyramine were quantitatively determined in the Arthus reaction, since the activity of histamine-N-methyltransferase (HMT), a major histamine-metabolizing enzyme that had been demonstrated to be inhibited by such biogenic amines in vitro, decreased significantly in the reaction site. The concentrations of serotonin, tryptamine, and dopamine were unchanged in dinitrochlorobenzene allergic and croton oil dermatitis except for a slight increase of tryptamine in the latter. Tyramine was unable to be demonstrated quantitatively in all specimens tested. The concentration of serotonin decreased to about 30% that of the control level until 1 hr, followed by a prominent increase to about two-fold at 6 hr after the initiation of the Arthus reaction accompanying with a concomitant decrease in HMT activity. However, the concentrations of tryptamine and dopamine were rather decreased in the reaction site, and the net decrease of two amines was far greater than the increased amount of serotonin. The decrease in HMT activity is not stoichiometrically well elucidated from these results, and therefore, the presence of other hypothetic inhibitory factors that are increased in the Arthus reaction should be suspected.