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Effect of Irradiation on Lymphoid Tissue Nucleic Acids in C57BL Mice^*

( Department of Radiology, Stanford University School of Medicine, San Francisco, Calif.)

In agreement with earlier observations, it was found that desoxyribonucleic acid phosphorus (DNAP) concentration increased with age in thymus and lymph nodes of normal C57BL mice, reaching a maximum at 90 days and decreasing thereafter. Concentration was higher in thymus than in lymph nodes at all ages studied.

The concentration of phosphorus in the fraction (RP) containing ribonucleic acid did not change appreciably with age and was the same in thymus and lymph nodes.

In C57BL mice treated systemically with four doses of 168 r at 8-day intervals, thymic concentration of DNAP decreased 40 per cent 4 days after treatment and remained significantly reduced through 142 days, at which time most of the thymuses were involved by lymphomas. In contrast, lymph node DNAP concentration, although depressed immediately after irradiation, returned to normal by 117 days after treatment. Irradiation resulted in a slight increase in RP concentration in both tissues when pooled data were examined.

Interpretation of these findings will require correlation with microphotometric determinations of DNA per nucleus in normal and irradiated lymphoid tissues.

^* This investigation was supported by a grant-in-aid from the National Cancer Institute, National Institutes of Health, Public Health Service, Bethesda, Md.

Received 6/10/52.