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

Naked mole-rats (Heterocephalus glaber) are fossorial, eusocial mammals tha t live in colonies averaging about 70 individuals. Metabolic regulation is of particular interest in this species because it is one of only two natura lly occurring small mammals that are hairless. Further, relative to other s mall mammals, naked mole-rats exhibit low body temperature (T-b) and weak c apacity to maintain T-b above the ambient temperature (T-a). The present st udy examined effects of T-a, norepinephrine (NE), and chronic food restrict ion on O-2 consumption (as a measure of metabolism) in naked mole-rats. Stu dies were performed in both awake and anesthetized animals. Metabolic rate decreased with increasing T-a over the range of 23-34 degrees C in awake mo le-rats, whereas in anesthetized animals rates of O-2 consumption were very low over this entire range of T-a and tended to increase with increasing T -a. Injections of NE led to rapid increases in metabolic rate at all T(a)s in anesthetized subjects and also at T-a = 34 degrees C in awake mole-rats. However, at T(a)s of 29 and 23 degrees C, awake subjects given NE showed l ittle stimulation of O-2 consumption beyond the already elevated baseline r ates observed at these T(a)s. During chronic restriction of food to 60-70% of their normal daily consumption mole-rats exhibited decreased rates of me tabolism; metabolic rate was not altered following several hours of acute f ood deprivation. Food consumption remained somewhat decreased after a perio d of chronic food restriction, even when animals were returned to ad lib co nditions. However, body weights returned to prerestriction values, despite the continued reduction in ad lib food intake. These observations suggest t hat mole-rats may be capable of long-lasting metabolic adaptations as a mea ns to cope with restricted food supply. These findings are discussed in rel ation to adaptation of this fossorial species to a habitat where food has a patchy distribution. Naked mole-rats, with their several unusual thermoreg ulatory and behavioral features, provide an intriguing model for studies of mammalian metabolic regulation. (C) 1999 Elsevier Science Inc.