Influence of noradrenaline on blood flow to brown adipose tissue in rats exhibiting diet-induced thermogenesis.

1. The influence of noradrenaline on regional blood flow was determined using radioactive microspheres in rats maintained on either stock diet or a palatable cafeteria diet. 2. Cardiac output and blood flow to brain, lungs, liver and skeletal muscle were similar for rats on the two diets. 3. Blood flow to total dissectable brown adipose tissue in control and cafeteria rats represented 1 and 2% of cardiac output respectively but these values rose to 7 and 15.5% during infusion of noradrenaline. 4. Arterial oxygen content was similar for all groups but the oxygen content of venous blood draining the interscapular brown adipose tissue fell to 6 ml O2/100 ml blood in control rats and 1 ml/100 ml in cafeteria rats after noradrenaline. 5. The total oxygen consumption of brown adipose tissue was calculated and found to account for 42% of the response to noradrenaline in control rats and 74% in cafeteria animals. The increments in the oxygen consumption of other tissues were almost identical in both groups and so all the diet-induced changes in thermogenic capacity can be attributed to increases in brown adipose tissue metabolism. 6. These findings demonstrate the quantitative importance of brown adipose tissue in diet-induced thermogenesis and confirm the similarities between diet and non-shivering thermogenesis.