[Study of the role of endogenous 3',5'-cyclic AMP in the radioresistance of the cell].

A survival period of irradiated rat thymocytes was studied after administration of several possible modifiers of intracellular 3',5'-cyclo AMP. Theophylline, which inhibits 3',5'-cyclo AMP phosphodiesterase, adrenaline, ATP and adenosine possessed a radioprotective effect if they were added before the irradiation or just immediately after it. Imidazole activated 3',5'-cyclo AMP phosphodiesterase and, being added within the above-mentioned periods, it shortened the survival period at the irradiated cells. When theophylline and imidazole were added within 30 min after the irradiation, their effect was completely altered: imidazole increased but theophylline decreased the survival period of the irradiated cells. 3',5'-cyclo AMP and N6-2'-0-dibutyryl-3',5'-cyclo AMP did not affect the viability of thymocytes after the irradiation.