Genetic selection of rats with high and low body temperatures

Body (core) temperature (T(c)) directly affects all biological processes, including sensitivity to toxic chemicals, development, aging, and drug metabolism. To understand how T(c) affects these processes it is necessary to alter T(c) independently of other physiological processes. The purpose of this study was to determine whether selective breeding techniques can be used to develop lines of rats with hyperthermic and hypothermic T(c)'s. T(c) and motor activity of 24 female and 23 male rats (parental line) of the NIH heterogenous stock were monitored by telemetry for 96h at a T(a) of 22 degrees C. The mean 24h T(c) of the male and female rats was 37.3 degrees C with a range of 37-38.2 degrees C. T(c) was not correlated with motor activity or body weight. Pairs with the lowest and highest T(c)'s were selected for breeding. The F1 generation consisted of 10 offspring from the hyperthermic group and 20 from the hypothermic group. They were implanted with transmitters at 60d of age. T(c) of rats derived from the hyperthermic parental line had a significantly warmer T(c) than the rats derived from the hypothermic parental line. Motor activity was significantly higher in the hyperthermic F1 males and hypothermic F1 females. Breeding of hyperthermic and hypothermic rats has shown that adult offspring of the fourth generation maintain significantly different core temperatures but have similar patterns of motor activity. The results demonstrate that T(c) is heritable and that it should be feasible to develop lines of rats that regulate T(c) above or below normal.