Regulation of food intake by metabolic fuels in white-crowned sparrows

Migratory birds rely on increased fat storage and fatty acid utilization to meet seasonal changes of energy expenditure and as a result increase food intake and fat stores before migration. To determine whether their feeding behavior is sensitive to carbohydrate and/or fatty acid utilization, white-crowned sparrows maintained on short daylength (9L15D) were injected intraperitoneally with 2-deoxy-D-glucose (2-DG) or 2,5-anhydro-D-mannitol (2,5-AM). Low doses of 2-DG (25 or 50 mg/kg) had no effect on food intake, and higher doses (100 or 300 mg/kg) significantly suppressed feeding after 1 and 2 h. No dose of 2-DG increased meal size. Similarly, low doses of 2,5-AM (25, 50, or 100 mg/kg) had no effect on food intake, and higher doses (300 and 600 mg/kg) significantly suppressed intake. These data suggest that decreased carbohydrate metabolism does not elicit feeding in this species. Importantly, these drugs, as well as insulin and glucagon, were demonstrated to increase plasma fatty acids as well as to decrease feeding. Injections of tributyrin (100, 300, 600, or 2,000 mg/kg i.p.) or glycerol (300, 450, and 600 mg/kg) also significantly suppressed 60-min and 120-min food intake dose dependently in these birds, and equimolar glucose (1,200 mg/kg) had no effect. We conclude that feeding by the white-crowned sparrow is unresponsive to manipulations of carbohydrate metabolism and is decreased after manipulations that increase plasma lipids.