Fig. 3. Plasma C-peptide, B glucagon and C serum 3-OMG concentrations following intragastric administration of 3 g (Trp-3) or 1.5 g (Trp-1.5) tryptophan, or control, in participants with type 2 diabetes.
(A) After tryptophan alone (i.e. t=−31 to −1min), there was an effect of treatment on C-peptide AUC−31 to −1min (P=0.002), which tended to be greater after Trp-3 (*P=0.06), and was greater after Trp-1.5 (**P=0.002), compared with control. There was also an effect on C-peptide at t=−1min (P=0.01), which was greater after both Trp-3 and Trp-1.5 compared with control (*P<0.05 for both). Following the mixed-nutrient drink (i.e. t=0 to 120min), there was an effect of treatment on C-peptide AUC−1 to 120min (P=0.01), which tended to be greater after Trp-1.5, but not Trp-3 (***P=0.06). (B) After tryptophan alone, there was an effect of treatment on fasting glucagon AUC−31 to −1min (P=0.04), however, this was lost on post-hoc comparisons. There was also an effect on glucagon at t=−1min (P=0.007), which tended to be greater after Trp-3 compared with control (*P=0.07). Following the mixed-nutrient drink, plasma glucagon rose on all days. However, there was no effect of treatment on glucagon AUC−1 to 120min, or a treatment*time interaction. (C) There was no effect of treatment on serum 3-OMG AUC0 to 120min, or a treatment*time interaction. Data are expressed as mean±SEM; n=12. Data were analysed using general linear model mixed-model analysis, with baseline as covariate, and repeated-measures ANOVA, adjusted for multiple comparisons using Bonferroni correction.