RADIOPROTECTION BY DMSO AGAINST THE BIOLOGICAL EFFECTS OF INCORPORATED RADIONUCLIDES IN-VIVO - COMPARISON WITH OTHER RADIOPROTECTORS AND EVIDENCE FOR INDIRECT ACTION OF AUGER ELECTRONS

Dimethyl sulfoxide (DMSO) was studied for its capacity to protect agai nst the biological effects of chronic irradiation by incorporated radi onuclides. Spermatogenesis in mice was used as experimental model and spermatogonial cell survival was the biological endpoint. DMSO was inj ected intratesticularly 4 h prior to a similar injection of the radioc hemical and the spermhead survival determined. Iodine-125 was localize d in either the cytoplasm (H(125)IPDM) or in the DNA ((125)IUdR) of th e testicular cells. Protection was observed against the high-LET type effects of DNA-bound I-125 as well as the low-LET effects of cytoplasm ically localized I-125 with dose modification factors (DMF) of 3.1 +/- 1.0 and 4.4 +/- 1.0 respectively. No protection (DMF = 1.1 +/- 0.1) w as observed against the effects of high-LET 5.3 MeV alpha particles of Po-210. The present findings provide supporting evidence that the mec hanism responsible for the extreme biological damage caused by DNA-bou nd Auger emitters is largely radical mediated and therefore indirect i n nature.