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Endocrine Abstracts (2014) 34 APW1.1 | DOI: 10.1530/endoabs.34.APW1.1

Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden.


The advent of mice as the most common animal used for metabolic studies was caused by the possibility to perform gene manipulations in this species (which first very recently has become possible in the previously most studied animal: the rat). Although the mouse in many ways would seem just to be a smaller version of the rat, the smaller size indirectly has added a confounding factor to interpretation of metabolic studies. The reason is that the environmental temperatures under which we study mice and rats are similar – but their thermoregulation is different. Temperatures around 20 °C are very cold for mice; they have to constantly increase their metabolism by some 50–75% in order to compensate for their heat loss (as compared to their metabolism at thermoneutrality, around 30 °C); for a rat, these temperatures are much closer to thermoneutrality. The extra heat production is generally caused by a recruitment and constant activation of brown adipose tissue. This constant extra heat production means that if any other thermogenic mechanism would be activated, the mouse would immediately diminish its brown-fat-derived heat so that there will be no metabolic effect of any alternative thermogenic mechanism; likely this phenomenon has led to several metabolic alterations being overlooked. Conversely, it would be realized that any change causing a decrease in e.g. skin or hair/fur appearance may appear as stimulating thermogenesis in a molecular way – whereas the increased heat production may just be ‘physical’, due to increased heat loss. Indeed, reports that activators of brown or brite/beige adipose tissue lead to increased metabolism and increased body temperature may be reporting the cause of brown/brite/beige adipose activation rather than the consequence. Due to the large effects on metabolism of this chronic cold exposure ‘normal’ mice endure, remarkable ‘humanizations’ of mouse metabolism may occur just by keeping mice at thermoneutrality.

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