Concerning the Mechanism of the Increased RNAse Activity in Lymphatic Cells Following Whole-body Irradiation

Summary

The RNAse content (i.e. total enzymatic activity after removal of inhibitors and disruption of mitochondria) was measured at 4, 28 and 48 hrs after whole-body irradiation with 400 and 1000 r in a number of organs of the rat. No changes were observed in the liver and kidney, and only small changes in the brain. In spleen, the activity of the organ as a whole did not rise, but the concentration per cell increased up to four times. In the thymus, the RNAse activity of the whole organ went up, and because of the large cell destruction this meant that the activity per cell in the irradiated organ increased as much as four hundred times after 1000 r. The new cells which repopulate the thymus and spleen at nine days after 400 r have normal RNAse contents.

The increase of the RNAse content per cell in the spleen following whole-body radiation seems to be an abscopal effect due to the irradiation of the head of the animal, because the same increase in RNAse is obtained when only the head is exposed, while a small increase only is found if the head is shielded, but the rest of the body irradiated.

In the thymus abscopal factors also play a part in the increase in RNAse; head shielding reduces the increase in RNAse per cell to a small fraction of that found after whole-body irradiation, but does not entirely prevent it. Irradiation of the head only increases the RNAse content of the thymus, but not to the same extent as whole-body irradiation.

Cell destruction in both the spleen and thymus is not affected by head shielding and the same loss in weight and DNA-content occurs as for whole-body irradiation, and the increase in RNAse cannot therefore play an important role in the interphase death of the lymphatic cells in spleen and thymus. It is suggested that the increase in RNAse of the cells that survive radiation is due to increased synthesis induced by radiation stimulation of the neuro-endocrine system.