Effect of tryptophan on the utilization of intra-duodenally infused labelled glucose in piglets given food at 1·35 times maintenance energy

Abstract

AbstractTwo experiments were conducted. The first, studied the chronic effect of tryptophan (trp) on glucose disposal and the second, the acute effect of trp on glucose disposal. In experiment 1, 12 piglets were allocated either to a trp deficient diet (T0) or a trp adequate diet (T1). After 14 days a 240-min intraduodenal infusion of glucose (130 µmol/kg per min) associated with D-(U-14C) glucose (1·18 kBq/kg per min) and an intrajugular infusion of D-(6-3H) glucose (1·85 kBq/kg per min) were started. In experiment 2, 18 piglets were given a trp adequate diet (T1) for 14 days. The piglets were then divided into two groups and received an intraduodenal infusion of either glucose (130 µmol/kg per min) or glucose plus trp (0·53 µmol/kg per min) for 240 min. At the same time an intrajugular infusion of D-(U-14C)glucose (1·48 kBq/kg per min) and D-(6-3H)glucose (2·59 kBq/kg per min) was given to all piglets. Blood samples were taken at regular intervals during the infusions for the measurement of plasma concentrations of insulin, glucose, lactate and blood specific activities of14C-glucose,14C-lactate,3H-glucose and3H-lactate. At the end of the infusion, samples were taken for the measurement of the accumulation of14C and3H in glycogen. In experiment 1, plasma insulin concentrations were higher in the T0 compared with the T1 group (at 30 min respectively, 837·7 (s.e.56·6) v. 404·9 (s.e.56·6) pmol/l,P< 0·001). Glucose concentrations were also higher in T0 compared with T1 (at 30 min respectively, 10·9 (s.e. 0·54) v. 9·3 (s.e. 0·54) mmol/l,P< 0·05). Glucose flux was unaffected by trp in both experiments. The accumulation of labelled glucose into liver and carcass glycogen was not affected by trp. The route of administration of glucose label had a significant effect on the percentage of label accumulated in liver glycogen. When both14C and3H were infused into the jugular vein there was no difference in the accumulation of the two tracers in liver glycogen (22·7 v. 21·8% of that infused,P> 0·05, respectively). However, when 14C was infused into the duodenum and3H into the jugular vein, accumulation into liver glycogen was higher for14C compared with3H (19·9 v. 15·6%,P< 0·001, respectively). In conclusion, trp does not appear to influence glucose disposal measured at the end of a 240 min intraduodenal glucose infusion. Contrary to results published from experiments with rats the indirect pathway for glycogen synthesis (glucose→lactate→glycogen) does not appear to occur in underfed piglets.