Influence of a mixed meal on splanchnic and interscapular energy expenditure in humans

Pulmonary, splanchnic, and interscapular O2 uptake was studied in 14 male volunteers before and for 90 min after a mixed meal. Thermistor catheters were inserted into a hepatic vein, the azygous vein, the pulmonary artery, and the aorta. Systemic and regional blood flows were determined during indirect calorimetry measurements and recordings of blood temperature. After the meal, pulmonary O2 uptake rose by 33-49 ml/min and splanchnic O2 uptake increased by 16-25 ml/min. In the azygous region O2 uptake did not increase significantly. Cardiac output increased after the meal by 1.1-1.5 l/min and splanchnic blood flow rose by 0.4-0.9 l/min. Azygous venous blood flow increased from 130 +/- 19 ml/min to 163 +/- 23 ml/min. In relation to splanchnic O2 uptake, the blood-drained splanchnic heat was low, 11 +/- 1 J/ml, and decreased to 7 +/- 1 J/ml after the meal. We conclude that after a mixed meal approximately one-half of the rise in O2 uptake occurs in the splanchnic organs; azygous-drained tissues, including possible interscapular brown adipose tissue, contribute minimally. The amount of heat drained with blood from the splanchnic region was low in relation to the splanchnic O2 uptake, indicating that splanchnic heat may be dissipated by routes other than the perfusing blood.