Intragastric tryptophan reduces glycemia after glucose, possibly via glucose-mediated insulinotropic polypeptide, in early-weaned piglets.

The aim of this experiment was to investigate the influence of oral tryptophan on insulin, glucose-mediated insulinotropic polypeptide and glucose concentrations in early-weaned piglets. Piglets were given by intragastric infusion, at the same level of feeding, either a tryptophan-deficient or tryptophan-adequate diet for 22 d. During the experiment blood samples were taken after intragastric infusion of 1) the accustomed meal, 2) a glucose plus tryptophan load and 3) a glucose load. Plasma samples were analyzed for insulin, glucose-mediated insulinotropic polypeptide, glucose and lactate. After the accustomed meal plasma insulin concentrations were augmented and liquid gastric emptying faster in pigs fed tryptophan-adequate compared with tryptophan-deficient diets (P < 0.05) but glucose-mediated insulinotropic polypeptide, glucose and lactate were unaffected. The addition of tryptophan to a glucose load increased glucose-mediated insulinotropic polypeptide and reduced glucose in both tryptophan-adequate and tryptophan-deficient diet fed pigs (P < 0.05). Piglets adapted to the tryptophan-adequate diet had a greater glucose-mediated insulinotropic polypeptide response to intragastric glucose plus tryptophan than piglets adapted to the tryptophan-deficient diet. Adaptation to a tryptophan-adequate diet seems to increase the release of glucose-mediated insulinotropic polypeptide due to infusion of a tryptophan-adequate compared with a tryptophan-deficient diet. The addition of tryptophan to a glucose load reduces the level of glycemia, possibly through glucose-mediated insulinotropic polypeptide-mediated glucose disposal.