Hormonal control of postprandial thermogenesis in dogs

The role of catecholamines, insulin, and thyroid hormones on postprandial thermogenesis was determined in dogs. O2 consumption (VO2) and respiratory quotient (RQ) were continuously monitored 1 h before and 2 h after a 1,016-kcal meal under the three following experimental conditions corresponding to 1) normal feeding, 2) sham feeding (with food deflected into an esophageal pouch), and 3) tube feeding intragastrically. A first phase (cephalic phase), lasting at least 45 min, was observed during both normal and sham feeding, whereas a second phase (digestive phase), occurred in both normal and tube feeding. Increases of 260% for norepinephrine (NE) were found during the cephalic phase in both normal and sham feeding. Epinephrine (E) increased by 425 and 600% during this early phase in normal and sham feeding, respectively. No change in plasma catecholamines was found in the tube-feeding experiment. Large increases of 75 and 39 microU/ml of insulin occurred early after the meal in both normal and sham feeding, whereas insulin increased only after 30 min in tube feeding. Thyroxine and triiodothyronine were not changed with any feeding experiment. Insulin change was positively correlated with NE and E changes rather than with glucose change during the cephalic phase after feeding. The results suggest an important role of catecholamines in the increased postprandial thermogenesis during the cephalic phase with a possible modulating effect of insulin.