Rats were contained in holders of Bollman type which were constructed of polyform end plates that were joined by Lutice rods to form a cylindrical space for the animals, 18 cm long by 6.2 cm in diameter.
A base plate of Polyfoam was located between the two end plates to provide a footrest.
Animals that received 27.7 cal/min (4.5 mW/kg) for 30 min exhibited an initial transient increase in colonic and skin temperatures but no changes in other functions. Animalsirradiated at 40.1 cal/min (6.5 mW/kg) had greater increases in colonic and skin temperatures immediately after exposure, followed by overcompensation and lower than normal colonic temperatures for about 3 h. The metabolic rate was depressed in this group of rats for 3 h. Bradycardia developed within 20 min after irradiation and persisted for about 3 h. Rats that received 68.2 cal/min (11.1 mW/kg) for 30 min had responses similar to those of the 40.1 cal/min group, but the alterations were more severe and lasted longer. Additionally, a number of transientabnormalities were observed in the ECG tracings of rats that had received the highest dose, including irregular rhythms and incomplete heart block. The physiological changes found in this study can be attributed to the heating induced by irradiation.