GLUCAGON-LIKE PEPTIDE-1(7-36)AMIDE AND GLUCOSE-DEPENDENT INSULINOTROPIC POLYPEPTIDE SECRETION IN RESPONSE TO NUTRIENT INGESTION IN MAN - ACUTE POSTPRANDIAL AND 24-H SECRETION PATTERNS

The acute effects of different macronutrients on the secretion of gluc agon-like peptide-1(7-36)amide (GLP-1(7-36)amide) and glucose-dependen t insulinotropic polypeptide (GIP) were compared in healthy human subj ects. Circulating levels of the two hormones were measured over a 24-h period during which subjects consumed a mixed diet. In the first stud y, eight subjects consumed three equicaloric (375 kcal) test meals of carbohydrate, fat and protein. Small increases in plasma GLP-1(7-36) a mide were found after all meals. Levels reached a maximum 30 min after the carbohydrate and 150 min after the fat load. Ingestion of both ca rbohydrate and fat induced substantial rises in GIP secretion, but the protein meal had no effect. In a second study, eight subjects consume d 75 g glucose or the equivalent portion of complex carbohydrate as bo iled brown rice or barley. Plasma GIP, insulin and glucose levels incr eased after all three meals, the largest increase being observed follo wing glucose and the smallest following the barley meal. Plasma GLP-1( 7-36)amide levels rose only following the glucose meal. In the 24-h st udy, plasma GLP-1(7-36)amide and GIP concentrations were increased fol lowing every meal and remained elevated throughout the day, only falli ng to fasting levels at night. The increases in circulating GLP-1(7-36 )amide and GIP levels following carbohydrate or a mixed meal are consi stent with their role as incretins. The more sustained rises observed in the daytime during the 24-h study are consistent with an anabolic r ole in lipid metabolism.