Role of Histaminase and Corticosterone on the Depletion of Tissue Histamine in the Irradiated Rats

The relationship between histamine contents and histaminase activities of the liver, small intestine, kidney, blood plasma and lung of rats exposed to 650 R of whole-body X-irradiation was examined. There was no correlation between these parameters in the liver and small intestine. In contrast, a negative correlation between these parameters was found in the kidney and the lung at 2, 4 and 7 days after irradiation. In particular, the histaminase activity of the lung increased significantly during the first few days after irradiation, reaching the maximum level of 200% of the control on day 4, and returned to the control level by day 7. Concomitantly, a gradual decrease in the histamine content in this organ was observed. Another important observation relates to the role of adrenocortical function on the activation of lung histaminase. Histaminase activity of the lung, which normally increased after irradiation of the intact rats, failed to increase when the animals had been adrenal-ectomized prior to the exposure to radiation. Data also showed that the activity of this enzyme elevated significantly when adrenal-ectomized rats were administered with corti-costerone for 3 days. On the basis of these observations, significant roles of corticosterone and histaminase in the depletion of tissue histamine from irradiated rats were discussed.