Thermoregulatory responses of unanesthetized rats exposed to gravitational fields of 1 to 4g

Rats exposed to 2g environments (achieved by centrifugation) exhibit a decreased ability to maintain colonic temperature (Tco) when challenged with a 1 hr drop in ambient temperature (Ta). As an extension of this work the present study considers whether the altered ability to maintain Tco is proportional to the magnitude of the acceleration field in the range from 1g-4g, and whether the magnitude of the decreased thermoregulatory ability is related to the onset time of the temperature drop relative to that of the acceleration. Male, Sprague-Dawley rats were instrumented on the experimental day with thermistors for measuring Tco. The unanesthetized rat was then placed in a plexiglas chamber, positioned on a centrifuge 1.37 m in radius, and exposed to 1.5, 2, 2.5, 3, 3.5, or 4g for 5-7 hrs. The exposure to reduced temperature (Ta = approximately 7 degrees C) for 1 hr began 3 hrs after initiation of centrifugation. These experiments indicated that the magnitude of the cold-induced drop in Tco was linearly related to the acceleration field. The effect of a specific stressor (cold) on the thermoregulatory system is therefore a direct function of the gravitational field.