VITAMINS AS RADIOPROTECTORS IN-VIVO .2. PROTECTION BY VITAMIN-A AND SOYBEAN OIL AGAINST RADIATION-DAMAGE CAUSED BY INTERNAL RADIONUCLIDES

Tissue-incorporated radionuclides impart radiation energy over extende d periods of time depending on their effective half-lives. The capacit y of vitamin A dissolved in soybean oil to protect against the biologi cal effects caused by internal radionuclides is investigated. The radi ochemicals examined are DNA-binding (125)IdU, cytoplasmically localize d H(125)IPDM,and the a-particle emitter Po-210 citrate. As in our prev ious studies, spermatogenesis in mice is used as the experimental mode l and spermatogonial cell survival is the biological end point. Surpri singly, soybean oil itself provides substantial and equal protection a gainst the Auger effect of (125)IdU, which is comparable to a high-LET radiation effect, as well as the low-LET effects of H(125)IPDM, the d ose modification factors (DMFs) being 3.6 +/- 0.9 (SEM) and 3.4 +/- 0. 9, respectively. The protection afforded by the oil against the effect s of 5.3 MeV alpha particles emitted by Po-210 is also significant (DM F = 2.2 +/- 0.4). The presence of vitamin A in the oil further enhance d the radioprotection against the effect of (125)IdU (DMF = 4.8 +/- 1. 3) and H(125)IPDM (DMF = 5.1 +/- 0.6); however, no enhancement is prov ided against the effects of alpha particles. These interesting results with soybean oil and vitamin A, together with data on the subcellular distribution of the protectors, provide clues regarding the mechanist ic aspects of the protection. In addition, the data for vitamin A reaf firm our earlier conclusion that the mechanism by which DNA-bound Auge r emitters impart biological damage is primarily indirect in nature.