The gut takes nearly all: threonine kinetics in infants

Abstract

Background:Threonine is an essential amino acid that is abundantly present in intestinally produced glycoproteins. Animal studies show that intestinal first-pass threonine metabolism is high, particularly during a restricted enteral protein intake.Objective:The objective of the study was to quantify intestinal first-pass threonine metabolism in preterm infants during full enteral feeding and during restricted enteral intake.Design:Eight preterm infants (x̄ ± SD birth weight: 1.1 ± 0.1 kg; gestational age: 29 ± 2 wk) were studied during 2 periods. During period A, 40% of total intake was administered enterally and 60% was administered parenterally. Total threonine intake was 58 ± 6 μmol · kg−1 · h−1. During period B, the infants received full enteral feeding, and the total threonine intake was 63 ± 6 μmol · kg−1 · h−1. Dual stable-isotope tracer techniques were used to assess splanchnic and whole-body threonine kinetics.Results:The fractional first-pass threonine uptake by the intestine was remarkably high in both periods: 82 ± 6% during partial enteral feeding and 70 ± 6% during full enteral feeding. Net threonine retention was not affected by the route of feeding.Conclusion:In preterm infants, the splanchnic tissues extract a very large amount of the dietary threonine intake, which indicates a high obligatory visceral need for threonine, presumably for the purposes of synthesis.