DNA-synthesis in the rat thymus after focal thermolesions on abdominal organs

The changes in the DNA-synthesis of lymphocytes in the different zones of the rat thymus were autoradiographically studied with 3H-thymidine after focal thermonecroses (740 degrees C/4 sec) on abdominal organs and sham operation (laparotomy). A single thermolesion was performed in separate groups of rats on the liver and spleen, whereas a third group received multiple heat lesions (liver, kidney, stomach wall). A slight decrease of the labeling index occured during the first 36 h after the sham operation and was attributed to an unspecific stress effect leading to an increased release of corticosterones. The most remarkable and contrasting result was the observation that after thermonecroses a decrease of the labeling index of thymus-lymphocytes did not happen during the first 48 h but rather a marked increased with a maximum on the fifth day. It was concluded that the stimulated DNA-synthesis in the thymus might be related to a cell mediated immune response against thermocoagulated tissue components or to an immediate T-cell dysfunction, which is known to develop after burns. In both cases the thymus might react with an increased division and maturation of lymphocytes regulated through a feed-back mechanism.