Dietary Supplementation of dl-Methionine Potently Induces Sodium-Dependent l-Methionine Absorption in Porcine Jejunum Ex Vivo

Abstract

ABSTRACTBackgroundMethionine is an essential amino acid (AA) with many fundamental roles. Humans often supplement l-Met, whereas dl-Met and dl-2-hydroxy-4-(methylthio)butanoic acid (dl-HMTBA) are more frequently used to supplement livestock.ObjectivesThe study aimed to investigate whether dietary Met source alters the absorptive capacity for Met isomers in the small intestine of piglets.MethodsA total of 27 male 10-wk-old piglets in 3 feeding groups received a diet supplemented with 0.21% dl-Met, 0.21% l-Met, or 0.31% dl-HMTBA to meet the Met + cystine requirement. After ≥10 d, absorptive fluxes of d-Met or l-Met were measured at a physiological concentration of 50 μM and a high concentration of 5 mM in duodenum, middle jejunum, and ileum ex vivo. Data were compared by 2-factor ANOVA.ResultsAcross diets, fluxes of both Met isomers at both tested concentrations increased from duodenum to ileum by a factor of ∼2–5.5 (P < 0.05). Pigs supplemented with dl-Met had greater (P < 0.085) absorptive fluxes at 50 μM l-Met (0.50, 2.07, and 3.86 nmol · cm−2 · h−1) and d-Met (0.62, 1.41, and 1.19 nmol · cm−2 · h−1) than did pigs supplemented with dl-HMTBA (l-Met: 0.28, 0.76, and 1.08 nmol · cm−2 · h−1; d-Met: 0.34, 0.58, and 0.64 nmol · cm−2 · h−1) in duodenum, jejunum, and ileum, respectively. Only in jejunum of dl-Met-fed pigs, fluxes at 50 μM l-Met were reduced by the omission of luminal Na+ (from 3.27 to 0.86 nmol · cm−2 · h−1; P < 0.05) and by a cocktail of 22 luminal AAs (to 1.05 nmol · cm−2 · h−1; P < 0.05).ConclusionsDietary supplementation of dl-Met increases the efficiency of l-Met and d-Met absorption at physiologically relevant luminal Met concentrations along the small intestine of pigs, including a very prominent induction of an Na+-dependent transport system with preference for l-Met in the mid-jejunum. Dietary supplementation with dl-Met could be a promising tool to improve the absorption of Met and other AAs.