The effect of brown fat removal on the development of obesity in Zucker and Osborne-Mendel rats.

Removal of significant amounts of brown fat in young Zucker rats maintained at room temperature triggered compensatory changes in the remaining brown fat depots. These changes, which occurred to a greater extent in the lean than in the obese rats, enhanced the thermogenic potential of the remaining depots, thus possibly accounting for the lack of increased adiposity in these lipectomized rats. When the Zucker rats were maintained in the cold, rather than at room temperature, their ability to compensate for removal of the scapular brown fat was compromised, particularly in the obese animals. Under such conditions, the amount of functional brown fat was significantly reduced, and the amount of body fat elevated. In the lipectomized Zucker rats, this increase in adiposity was accompanied by increased body mass. In contrast, in the cold-exposed Osborne-Mendel rats, where lipectomy was not accompanied by compensatory increases in the mass and cellularity of the remaining brown fat depots, increased body fat occurred in the absence of any increase in food intake or in total body mass.