AET AS A RADIOPROTECTIVE AGENT AT THE CELLULAR LEVEL

¹ Radiological Research Laboratory, Department of Radiology, College of Physicians and Surgeons, Columbia University, New York 27, N. Y.

1. AET (S,2-aminoethyhisothiourea-Di-HBr) was used in a concentration just below the threshold toxicity level, to determine whether it might afford any radioprotection for the haploid Arbacia egg exposed to 50,000 r gamma radiation prior to fertilization with normal sperm.

2. Arbacia eggs could be fertilized in 3 mgm.% AET and would cleave and develop, both in time and manner comparable to the controls in pure sea water. Toxicity was indicated above 5 mgm.%, particularly after irradiation.

3. Arbacia eggs exposed to 50,000 r gamma rays showed a delay in the initiation of the first cleavage with ultimate cleavage reaching only 11% and abnormalities reaching 18%. Not a single egg so exposed ever reached the pluteus stage. The delay in the initiation of the first cleavage was also reduced by a delay in fertilization, and the percentage of ultimate cleavage was improved.

4. The optimum conditions provided were: Exposure to 3 mgm.% AET in sea water for 10 minutes prior to and 10 minutes during gamma irradiation to 50,000 r, and yet this allowed no improvement in cleavage time, degree of membrane elevation, or development. Not a single egg thus treated reached either the pluteus or gastrula stages.

5. It is concluded that while AET has proven to be radioprotective for the adult mammal, this protection (survival) may not be effected through individual cells but through tissue or organ regeneration. However, extrapolation is always hazardous and AET may be cell- or species-specific. The haploid Arbacia cell (cytoplasm and nucleus) is not subject to any protective action from AET.