Ventromedial hypothalamic lesions abolish compensatory reduction in energy expenditure to weight loss.

Weight loss through caloric restriction produces compensatory reductions in the whole body energy expenditure of normal rats. The present experiment determined whether rats who had become obese after ventromedial hypothalamic (VMH) lesions displayed this metabolic defense of body weight. Obese VMH-lesioned and normal-weight control female rats were assigned to one of three weight maintenance conditions (100, 90, and 80% of previously maintained body weight). Postabsorptive oxygen consumption was then measured by open-circuit respirometery while, simultaneously, behavioral activity was measured by stabilimeter. A marked decline in resting energy expenditure and behavioral activity, seen in control rats after weight loss, was absent in VMH-lesioned rats. These results suggest that VMH lesions impair the ability to adjust energy expenditure in response to alterations in nutritional status, a response that normally serves to stabilize body weight at a regulated level.