Metabolism of Histidine in X-irradiated Rats in Relation to Histamine and Diamine Oxidase

Summary

The effect of x-irradiation (600 R) on rats has been ascertained with reference to histamine by assessing the activities of rat-liver enzymes and following-up radioactivity in vivo in the metabolites after intraperitoneal injection of histidine-U-¹⁴C.

Rat-liver histidine decarboxylase showed enhanced activities immediately (4 hours) after irradiation, showing a decline at 24 hours and return to normal values at 48 hours. Liver histaminase, a diamine oxidase, showed a decrease at 4 hours with no variation from the control values at the other time-intervals. Histidase gave a similar response, but urocanase was unaffected by x-irradiation.

The recovery of radioactivity of administered histidine-U-¹⁴C in histamine was increased 2–5-fold in various organs, including liver, kidney and spleen. The increase in the labelling of histamine in vivo was maximum. Radioactivity in the other metabolites, namely, urocanic acid, imidazoleacetic acid and imidazoleacetic riboside and methylhistamine, was in accordance with the activities of the enzyme studied.