Evaluation of Histamine Formation and Catabolism in the Rat

Abstract

Male and female rats were given small amounts of radioactive histidine in daily subcutaneous injections and their histamine metabolism studied by analyses of the urinary excretion of nonradioactive as well as radioactive histamine and methylhistamine. The male rats excreted more radioactive and nonradioactive methylhistamine than the female rats. During the first days relatively smaller amounts of radioactive methylhistamine were excreted, particularly in the male rat, but later on they increased. Similar specific activity for histamine and methylhistamine was only seen some days after the injections of radioactive histidine had been discontinued. After a burn injury the urinary excretion of both radioactive and nonradioactive histamine and methylhistamine increased, largely in parallel, demonstrating a considerable increase in histamine formation without changes in methylation. It is concluded that simultaneous measurements in the rat urine of nonradioactive histamine and methylhistamine give results which agree in principle with those obtained by measuring radioactive histamine and methylhistamine after having injected radioactive histidine into the rats during some days. Measurements of the urinary excretion of radioactive histamine and methylhistamine during the first 24 hours after a single injection of radioactive histidine will mainly give information about histamine that has been recently formed in the rat body and excreted without, or after a brief period of storage. Analyses of the urinary excretion of nonradioactive histamine and methylhistamine appear to be highly suitable for obtaining quantitative information about the histamine metabolism in male and female rats.