The role of glucagon-like peptide-1 receptors in protein-induced suppression of food intake in rats

This research examined the hypothesis that suppression of food intake after protein ingestion in rats involves the Glucagon-Like Peptide-1 (GLP-1) receptors. The primary objectives were to determine (1) whether GLP-1 receptor activation with exendin-4 (Ex-4) affected suppression of food intake by proteins; (2) the components of proteins with which Ex-4 affect suppression of food intake; and (3) the effect of co-administering protein with Ex-4 on the relation between putative signals for protein-induced satiety and food intake. Four studies involving a total of twelve experiments were conducted. Rats were given treatments by intraperitoneal and/or intragastric routes, and food intake and metabolic responses were measured at predetermined times.;Both protein and Ex-4 reduced food intake when given alone. Co-administration resulted in suppression of food intake that is less than the sum of the suppression caused by each treatment alone, thus providing indirect evidence that protein-induced suppression of food intake involves activation of the GLP-1 receptor. This effect was observed after free amino acid mixtures, suggesting that amino acids arising from the digestion of protein are the primary signals mediating the involvement of the GLP-1 receptor in protein-induced suppression of food intake. Ex-4 also altered post-absorptive satiety signals arising from protein ingestion. Taken together, these results provide support for a role for GLP-1 receptors in protein-induced suppression of food intake in rats.