EFFECT OF CHRONIC INTRACEREBROVENTRICULAR INFUSION OF INSULIN ON BROWN ADIPOSE-TISSUE ACTIVITY IN FED AND FASTED RATS

OBJECTIVES: Carbohydrate feeding stimulates, and fasting decreases the sympathetic nervous system activity and brown adipose tissue (BAT) th ermogenesis, This study was performed to assess the hypothesis that th ese effects were secondary to changes in insulin concentrations in the central nervous system, METHODS: BAT sympathetic activity was assesse d by comparing H-3-GDP binding to isolated mitochondria of innervated and denervated interscapular BAT of three groups of 10 week old male W istar rats: food-restricted, 48 h fasted or ad libitum fed. During the three days preceding this measurement, animals received a continuous intracerebroventricular (icv) infusion of insulin (0.48 U/d) or vehicl e. RESULTS: In food-restricted rats, H-3-GDP binding to mitochondria o f innervated BAT was 41% higher than that to denervated BAT. Icu insul in did not stimulate H-3-GDP binding in innervated and denervated BAT. In 48 h fasted rats, H-3-GDP binding to mitochondria of innervated BA T was reduced by 30-50%, while the activity of denervated BAY was mini mally affected. Icy insulin did not prevent this fasting-induced drop in BAT. In rats fed ad libitum, icv insulin decreased food intake by 1 7% (P < 0.05) and increased H-3-GDP binding to innervated BAT by 27% ( P < 0.05). CONCLUSION: Intracerebroventricular insulin stimulates BAT activity in rats fed ad libitum but not in food-restricted or fasted r ats, This demonstrates that the decrease in BAT activity observed duri ng fasting is unlikely to be due to a decrease in insulin concentratio n in the nervous system.