Mutual absorptive interaction of D-glucose and D-galactose with L-Alanine in the intestine of broiler chickens offered a low-protein wheat-based diet

This study tested the hypothesis that growth retardation in broiler chickens fed low-protein wheat-based diets is linked to interactions between intestinal hexose and amino acid (AA) absorption. A total of 54 male Cobb 500 broilers were fed a three-phase low-protein wheat-based diet for ≥28 days (crude protein: -2% points of Cobb 500 recommendations). Apical jejunal uptakes of L-Alanine (L-Ala) were measured in Ussing chambers in the presence of 0, 20 or 100 mM luminal hexoses (D-glucose, D-galactose, D-fructose or D-mannose) and, conversely, D-glucose uptakes were measured in the presence of 0, 20 or 100 mM luminal L-Ala, each in the presence and absence of luminal Na⁺. L-Alanine uptakes were further measured after two preincubation lengths (3 min versus 30 min) with D-glucose or D-galactose and three transepithelial potential differences (PD_t; open circuit, PD_t = 0 mV or PD_t = -50 mV) co-applied with 100 mM luminal D-galactose. With the exception of a statistical trend for L-Ala uptake in the copresence of D-mannose (P = 0.087), apical uptakes of L-Ala and D-glucose were generally higher in the presence vs. absence of Na⁺ (P < 0.05). Apical L-Ala uptakes showed no sodium × hexose concentration interaction with D-fructose and D-mannose. However, such interaction existed for luminal D-glucose and D-galactose (P < 0.05) where D-glucose or D-galactose decreased L-Ala uptakes solely in the presence of Na⁺ (P < 0.05). Vice versa, increasing luminal L-Ala concentrations decreased apical D-glucose uptakes solely in Na⁺-containing luminal solutions (sodium × Ala concentration, P = 0.011). Different preincubation lengths with hexoses had no interaction effect. However, a PD_t × sodium interaction (P = 0.013) revealed that the Na⁺-dependent portion of L-Ala uptakes was significantly reduced after a 3-min preincubation with 100 mM d-galactose at only -50 mV. The results demonstrate a bidirectional interaction of AA and glucose absorption in the broilers' jejunum that might be based on subapical sodium accumulation and may at least partially explain reduced growth performance in broilers fed low-protein wheat-based diets.