Chemical specificities and intestinal distributions of nutrient-driven satiety.

We measured intakes of sham- and naturally feeding rats during gut perfusions of nutrients. Our objectives were to determine 1) which nutrient products in gut lumen suppressed intakes; 2) how suppression by various nutrients is distributed along gut; and 3) whether time courses of suppression were similar among different nutrients. We found that satiating nutrients consisted of fatty acids only longer than 10 carbons, of monomeric carbohydrates only with affinity for the glucose transporter, and, among several amino acids, of only phenylalanine and tryptophan. Dimeric maltose had about the same potency as an isocaloric mixture of longer glucose polymers; since responses to either were blocked by a glucosidase inhibitor, each probably acted after hydrolysis to free glucose. Effective nutrients suppressed intakes about equally on infusion into duodenum vs. midgut, and the same nutrients also suppressed intakes when infused into colon. Food intakes were suppressed only while maltose was infused, not after it was stopped, but suppression persisted for 2 h after stopping perfusions with fatty or amino acids.