Radioprotective effect of different nucleosides and nucleotides, and mechanism of effect of adenosine

Adenosine and a majority of adenine mononucleotides have a radioprotective action; adenine and 2'-deoxyadenosine have no radioprotective effect, and that of 3',5'-cAMP only approaches the detectable level. Ribo- and deoxyribonucleosides and nucleotides of guanine, uracil, thymine, and cytosine have no protective action. Dypyridamol increases and alkylxanthines block the radiprotective effect of adenosine. So it follows that the radioprotective effect is realized via A-receptors of the plasmatic membrane external surface