DYNAMICS OF BROWN FAT THERMOGENESIS IN WEEK-OLD RATS - EVIDENCE OF RELATIVE STABILITY DURING MODERATE COLD-EXPOSURE

Neonates of many mammalian species, including humans, depend primarily on thermogenesis by brown adipose tissue as a defense against cold ch allenge. Although the steady-state thermogenic responses of brown adip ose tissue to various air temperatures are well known, the dynamic res ponses have received relatively little attention. In this article, we examine the relative stability of brown adipose tissue thermogenesis d uring brief perturbations of air temperature. Specifically, week-old r ats were allowed to settle at one of two levels of cold exposure. Thes e two levels were defined on the basis of previous work as being moder ate (30.5 degrees C) or extreme (23 degrees C). After pups had settled at these temperatures, they were exposed to positive or negative air temperature perturbations of approximately 3.7 degrees C. Pups experie ncing perturbations hum the moderate air temperature, unlike those exp osed to the extreme air temperature, exhibited organized thermogenic r esponses that allowed them to return quickly to their preperturbation conditions. These data suggest that brown adipose tissue thermogenesis is more stably controlled than has previously been suspected.