Glucocorticoids, the etiology of obesity and the metabolic syndrome

In mammals, glucocorticoid actions appear to have evolved to maintain and enhance energy stores to be used for life-saving gluconeogenesis. They act on the brain to stimulate search behaviors, palatable feeding and emotionally relevant memories, and they act on the body to mobilize stored peripheral energy and direct it to central depots that serve the substrate needs of the liver. Our work in rats shows that searching and intake of palatable foods (sucrose, saccharin and lard) are stimulated by corticosterone in a dose-related fashion. Adrenalectomized rats gain weight poorly, have low fat content, increased sympathetic neural and hypothalamo-pituitary-adrenal outflow, and altered behaviors. Replacement with corticosterone reverses these effects. Surprisingly, when such rats are provided with 30% sucrose to drink, in addition to saline, all of the usual effects of adrenalectomy are corrected without corticosterone. We hypothesize that there is a metabolic feedback system that decreases stress-responsiveness. Although we have not yet identified the signal associated with sucrose drinking, the weight of mesenteric fat correlates inversely with hypothalamic corticotropin-releasing factor (CRF). When rats eat lard and sucrose ad libitum, fat stores increase and CRF, ACTH and corticosterone responses are reduced. During stress, chow intake decreases but intake of lard and sucrose does not. Our current working model suggests that palatability signals and neural signals from fat stores act on brain to reduce activity in the central stress response system. Correlative results from a clinical study support the powerful role of small changes in glucocorticoids in type 2 diabetes.