PLASMA DIAMINE OXIDASE ACTIVITY AFTER SINGLE OR CHRONIC ADMINISTRATIONS OF HISTAMINE

Plasma diamine oxidase (DO) activity was tested in guinea pigs subjected to single or chronic administration of histamine (H). Single intraperitoneal injection of H in doses of 2 and 4 mg/kg induced an increase in DO activity for a period of 5 and 14 days, respectively. DO activity was increased for a similar period (12 days) after an 80-fold lower H dose administered by inhalation as an aerosol. In animals subjected to chronic H administration for 6-8 weeks (adapted animals), DO activity was inhibited, probably as a result of exhaustion of the reserve of pyrodoxal phosphate (PLP) the DO co-enzyme. Eight days after H administration to the adapted animals was discontinued, DO activity was found to be significantly higher than in the controls. PLP injection was followed by an increase in DO activity in control animals and prevented the block of its activity in animals exposed to H aerosol. The mechanism of enzymatic block in animals daily exposed to H aerosol and the importance of this time at which DO activity is tested in relation to the time of H administration are discussed. © 1969.