Brown adipose tissue thermogenesis is ‘suppressed’ during lactation in mice

Abstract

Brown adipose tissue is considered to be the main site of thermoregulatory non-shivering thermogenesis in the newborn of many mammalian species, in arousing hibernators, and in adult cold-adapted rats and mice^1–4. Several recent studies have now suggested that the tissue may also be important in the regulation of energy balance. Evidence has been obtained indicating that the ability of genetically obese (ob/ob and db/db) mice to become obese on a normal energy intake is mainly due to reduced brown adipose tissue thermogenesis^5–7, and a reduction in the activity of the tissue has also been observed in rats made obese by lesions of the ventromedial hypothalamus⁸. In contrast, increases in thermogenesis in brown adipose tissue have been implicated in the immediate thermic effect of food⁹ and in cancer cachexia¹⁰, and a substantial augmentation of the activity of the tissue has been demonstrated in rats and mice exhibiting regulatory diet-induced thermogenesis as a response to chronic voluntary over-feeding^11–14. Whether or not brown adipose tissue thermogenesis changes in other, more physiological, states where energy flux and metabolic efficiency are altered (independently of environmental temperature) has not been established. We now report that the thermogenic activity of brown adipose tissue is suppressed in mice during the ‘physiological hyperphagia’ of lactation, and show that this probably results in a substantial reduction in the energy requirement for maintenance of the lactating animal.