Modifications of animal response to Partial Body Hyperthermia (PBH) as a potent radioprotector: Relationships with animal age and sex

Currently available radio protectors are poorly tolerated in man. Thus, the use of the most promising agent, WR 2721 [S-2 (3-aminoprophylamino) ethylphosphoro thioic acid] has been limited due to its poor clinical tolerance. In a search for less toxic and/or without side effects agents, radioprotective effects of partial body hyperthermia (PBH) have been tested on Wistar rats of both sexes at different ages. Groups of male and female rats were irradiated [Total Body Irradiation (TBI)] in a perforated plexi-glass boxes using a 60Co source. The irradiation dose was 9 Gy which is considered as a lethal dose of 100% of animals (LD100) (the dose rate was = 80-85 rad.min-1). Irradiated animals were monitored for 2 weeks at least, and percentage of survival was calculated on the control groups. Partial Body Hyperthermia was carried out 20 hours prior to irradiation of 200-250 gr rats (by immersion of lower parts and legs of rats, in water bath at 43 centigrade for 1 h). Irradiated PBH treated animals were monitored for 30 days after irradiation and the survival percentage was calculated. Our results showed that PBH treatment, can be considered as a radioprotector. Moreover, the results of the undertaken study showed that this response changes as a function of animal age and sex. Thus, PBH was more effective on young rats (males and females), However, after 30 days of irradiation, PBH was more effective on males than females. The conclusion reached by this study is that animal response to PBH decreases with aging. Despite that the precise mechanism by which PBH induces retardation of death and enhance survival of rats is still obscure, Hyperthermia is known to enhance the immune response. Literature reveals that the productions of cytokines such as interferons and interleukins as well as natural killer cell activity are enhanced after hyperthermia. (author)