Factors influencing metabolic rate in naked mole-rats (Heterocephalus glaber).

Naked mole-rats (Heterocephalus glaber) are fossorial, eusocial mammals that live in colonies averaging about 70 individuals. Metabolic regulation is of particular interest in this species because it is one of only two naturally occurring small mammals that are hairless. Further, relative to other small mammals, naked mole-rats exhibit low body temperature (Tb) and weak capacity to maintain Tb above the ambient temperature (Ta). The present study examined effects of Ta, norepinephrine (NE), and chronic food restriction on O2 consumption (as a measure of metabolism) in naked mole-rats. Studies were performed in both awake and anesthetized animals. Metabolic rate decreased with increasing T. over the range of 23-34 degrees C in awake mole-rats, whereas in anesthetized animals rates of O2 consumption were very low over this entire range of Ta and tended to increase with increasing Ta. Injections of NE led to rapid increases in metabolic rate at all Tas in anesthetized subjects and also at Ta = 34 degrees C in awake mole-rats. However, at Tas of 29 and 23 degrees C, awake subjects given NE showed little stimulation of O2 consumption beyond the already elevated baseline rates observed at these Tas. During chronic restriction of food to 60-70% of their normal daily consumption mole-rats exhibited decreased rates of metabolism; metabolic rate was not altered following several hours of acute food deprivation. Food consumption remained somewhat decreased after a period of chronic food restriction, even when animals were returned to ad lib conditions. However, body weights returned to prerestriction values, despite the continued reduction in ad lib food intake. These observations suggest that mole-rats may be capable of long-lasting metabolic adaptations as a means to cope with restricted food supply. These findings are discussed in relation to adaptation of this fossorial species to a habitat where food has a patchy distribution. Naked mole-rats, with their several unusual thermoregulatory and behavioral features, provide an intriguing model for studies of mammalian metabolic regulation.