A HYPERCALORIC LOAD INDUCES THERMOGENESIS BUT INHIBITS STRESS RESPONSES IN THE SNS AND HPA SYSTEM

Caloric overingestion generates a sympathetic nervous system (SNS)-med iated increase in brown adipose tissue (BAT) thermogenesis; its effect on the hypothalamo-pituitary-adrenal (HPA) axis is unknown. To determ ine whether metabolic activation affects the HPA axis, male rats were provided palatable sucrose ad libitum. After 5 or 10 days of sucrose i ngestion, BAT and basal and restraint-induced HPA variables were measu red. Some rats were instrumented with temperature probes. BAT temperat ure and HPA axis responses to restraint were measured. Although calori c intake increased greater than or equal to 18%, body weight gain did not change after sucrose ingestion; DNA, protein, and uncoupling prote in increased in BAT depots, and white adipose tissues were heavier aft er both 5 and 10 days. During days 5-10, the BAT-core temperature diff erence was +0.30 degrees C in sucrose rats and -0.46 degrees C in cont rols (P < 0.05); this, together with the biochemical changes, shows pe rsistent activation of BAT by excess calories. Basal HPA measures were not altered. The sucrose group exhibited smaller BAT temperature and HPA responses to restraint on day 10; there was no HPA difference on d ay 5. We conclude that calorically mediated increases in BAT thermogen esis are independent of basal HPA activity; however, both systems resp ond concordantly to restraint stress. The diminished response to restr aint in both systems in sucrose-fed rats may result from signals indic ating increased energy stores.