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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Luminal Threonine Concentration Acutely Affects Intestinal Mucosal Protein and Mucin Synthesis in Piglets^1–3,

Department of Biochemistry, Memorial University of Newfoundland, St. John's, Canada A1B 3X9

^* To whom correspondence should be addressed. E-mail: rbertolo{at}mun.ca.

Intestinal mucin synthesis is sensitive to dietary threonine supply, which suggests that the gut's requirement for threonine may comprise a significant proportion of the whole body requirement. We used a continuously perfused gut loop model and intraluminal flooding dose technique in 6 young pigs to study the acute effects of varying luminal availability of threonine on intestinal protein and mucin syntheses. A complete amino acid mixture containing 0, 21, or 56 mg threonine/g total amino acids (whole body requirement ratio is 28 mg/g) was continuously perfused in isolated loops for 120 min, including a 30-min ³H-phenylalanine flooding dose. We measured fractional synthesis rates of total mucosal protein and mucin by analyzing ³H-phenylalanine incorporation. Fractional rates of total mucosal protein synthesis were higher in loops perfused with solutions containing threonine at 56 mg/g (66 ± 4%/d) compared with 0 mg/g (42 ± 9%/d) and 21 mg/g (53 ± 6%/d) (P < 0.05). For mucin, fractional rates of synthesis differed between 0 mg/g (323 ± 72%/d), 21 mg/g (347 ± 49%/d), and 56 mg/g (414 ± 31%/d) (P < 0.05). In addition, total proline and threonine concentrations in the protein hydrolysates increased with luminal threonine concentration (P < 0.05), indicating an increase in threonine- and proline-rich proteins. De novo synthesis of mucosal and mucin proteins is acutely sensitive to luminal threonine concentration, which demonstrates the importance of dietary amino acid supply to gut protein metabolism.

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