Some physiological aspects of temperature regulation in the normothermic and torpid hispid pocket mouse, perognathus hispidus

Abstract

1. 1. In Perognathus hispidus minimum heart and respiratory rates were 250 beats/min and 50 breaths/min. Their body temperature was between 36·8–38·7°C at an ambient temperature range of 5–34°C. The thermoneutral metabolic rate was 1·25 cc O 2/g per hr and occurred at ambient temperatures of 30·5–33·5°C (thermoneutrality). The thermal conductance was 0·201 cc O 2/g per hr per °C including heat lost by evaporation. 2. 2. During entry into torpor the heart rate of P. hispidus decreased prior to a decline in oxygen consumption and body temperature. Skipped heart beats, apnea and intermittent shivering were typical of the entrance phase. 3. 3. During torpor the heart rate and the oxygen consumption was 6–14 per cent and 3·5–13 per cent, of normothermic values at body temperatures of 12 to 20·3°C. Respiratory rate was irregular with prolonged apnea. When the ambient temperature dropped below 14°C, the body temperature of torpid animals tended to remain relatively constant. 4. 4. During arousal heart rate increased seven to twenty times and respiratory rate six to ten times, depending on the initial body and ambient temperature. Intensity of shivering was strongest during the middle part of arousal. Oxygen consumption was approximately double the normothermic value and the recorded maximum increase in oxygen consumption was fifty-seven times the torpid level. Maximum neck-abdomen temperature difference was 3·7°C and the fastest spontaneous arousal rate averaged 0·47C/min.