Exposure to Heavy Charged Particles Affects Thermoregulation in Rats

Rats exposed to 0.1-5 Gy of heavy particles (<tex-math>${}^{56}{\rm Fe}$</tex-math>, <tex-math>${}^{40}{\rm Ar}$</tex-math>, <tex-math>${}^{20}{\rm Ne}$</tex-math> or⁴ He) showed dose-dependent changes in body temperature. Lower doses of all particles produced hyperthermia, and higher doses of <tex-math>${}^{20}{\rm Ne}$</tex-math> and <tex-math>${}^{56}{\rm Fe}$</tex-math> produced hypothermia. Of the four HZE particles, <tex-math>${}^{56}{\rm Fe}$</tex-math> particles were the most potent and⁴ He particles were the least potent in producing changes in thermoregulation. The <tex-math>${}^{20}{\rm Ne}$</tex-math> and <tex-math>${}^{40}{\rm Ar}$</tex-math> particles produced an intermediate level of change in body temperature. Significantly greater hyperthermia was produced by exposure to 1 Gy of <tex-math>${}^{20}{\rm Ne}$</tex-math>, <tex-math>${}^{40}{\rm Ar}$</tex-math> and <tex-math>${}^{56}{\rm Fe}$</tex-math> particles than by exposure to 1 Gy of⁶⁰ Co γ rays. Pretreating rats with the cyclo-oxygenase inhibitor indomethacin attenuated the hyperthermia produced by exposure to 1 Gy of <tex-math>${}^{56}{\rm Fe}$</tex-math> particles, indicating that prostaglandins mediate <tex-math>${}^{56}{\rm Fe}\text{-particle-induced}$</tex-math> hyperthermia. The hypothermia produced by exposure to 5 Gy of <tex-math>${}^{56}{\rm Fe}$</tex-math> particles is mediated by histamine and can be attenuated by treatment with the antihistamines mepyramine and cimetidine.