Factors influencing the acute effect of food on oxygen consumption in the rat

The rise in resting oxygen consumption (VO2) during the 2-3 h following intragastric feeding (50 kJ [12 kcal]) was significantly greater in hyperphagic cafeteria-fed rats and hyperthyroid rats, but was markedly reduced in 3-day fasted and genetically obese Zucker rats, compared to their respective stock-fed controls. In control and hyperthyroid animals this response was almost completely abolished by administration of propranolol. In another group of rats, resting VO2 was elevated by 8 per cent after 12 h of cafeteria feeding and was maximally increased by 20 per cent after 2.5 days on the diet. In rats previously cold-adapted (15 days at 5 °C) the maximal response (20 per cent) to cafeteria feeding was seen after only 12 h on the diet. These results suggest that the acute thermic response to food involves a sympathetic activation of thermogenesis, similar to that induced by chronic hyperphagia and cold-exposure, and can be influenced by genetic background, plane of nutrition and thyroidal status.