Intravenous nutrient-induced satiety depends on feeding-related gut signals

To determine whether feeding-generated gut signals act in conjunction with intravenous nutrients to suppress food intake, nutrients were infused intravenously to dark-fed rats during different portions of the 12:12 h light-dark cycle. During 4-day test periods rats received 35.5-37 kcal/day of a solution containing 25% glucose-4.25% amino acids. Food intakes were reduced by 40.5 +/- 1.1 and 30.7 +/- 1.8 kcal or 110 and 87% of the calories infused in the dark (fed) phase over 8 and 12 h, respectively. When administered in the light phase while rats were fasted, 8- and 12-h infusions reduced food intake significantly less than in the dark: 21.3 +/- 1.1 and 19.6 +/- 0.7 kcal/day or only 57 and 55% of the infused calories, respectively. With 24-h infusions, as in previous studies, food intake was reduced by 24.5 +/- 2.1 kcal/day or 68% of the infused calories. These results suggest that gut signals generated by concurrent feeding act with intravenous glucose and amino acids to produce a more compensatory reduction in daily food intake.