Abstract
The cutaneous concentration of histamine and the specific activities of its degrading enzymes, histamine-N-methyltransferase (HMT) and diamine oxidase (DAO), were examined in the Arthus reaction sites induced in guinea pig skin, and kind of cells infiltrated in the lesional sites was also investigated. Histamine concentration revealed a prominent linear decrease at the early stage to about 15% of the control level, and recovered linearly to 85% 6 hours after the initiation without significant infiltration of mast cells and basophils, and no remarkable change was observed thereafter up to 48 hours. The activity of HMT, a major enzyme in the degradation of histamine having almost 15 times greater activity than that of DAO, sustained the control level till 1 hour, followed by a prominent linear decrease to 35% at 6 hours and to 10% at 48 hours. Another histamine degrading enzyme (DAO) activity increased to about 150% till 1 hour, and decreased linearily like the time course of HMT activity. These changes in enzyme activities seemed to well explain the quantitative change in histamine concentration in the reaction sites. The effect of released histamine in the lesional sites was also discussed.
