The Methionine Requirement Is Lower in Neonatal Piglets Fed Parenterally than in Those Fed Enterally

Abstract

The requirements for the sulfur amino acids (SAA), methionine (Met) and cysteine (Cys), have seldom been determined in neonates and to our knowledge have not previously been determined directly in parenterally fed neonates. The sulfur amino acids are catabolized largely in the liver and kidney, and their metabolism by the gut has been studied less frequently. In the present research, the enteral and parenteral Met requirement was determined, without dietary Cys, using the indicator amino acid oxidation (IAAO) technique. Piglets [n = 32, 2 d old, 1.66 +/- 0.13 kg (SD)] received elemental diets containing adequate energy, phenylalanine (Phe) and excess tyrosine, with varied Met concentrations and no Cys. Diets were infused continuously via intravenous or intragastric catheters. Phenylalanine oxidation was determined during a primed, constant infusion of L-[1-(14)C]-Phe, by measuring expired (14)CO(2) and plasma specific radioactivity of Phe. For both parenteral and enteral groups, Phe oxidation (% of dose) decreased linearly (P < 0.01) as Met intake increased, then became low and unchanging. Using breakpoint analysis, the Met requirement was estimated to be 0.42 and 0.29 g/(kg. d) for enteral and parenteral feeding, respectively. Breakpoint analysis using absolute phenylalanine oxidation [ micro mol/(kg. h)] resulted in an estimation of the Met requirement of 0.44 and 0.26 g/(kg. d) for enteral and parenteral feeding, respectively. These data show that the parenteral Met requirement is approximately 69% of the enteral requirement and suggest that extraction of SAA by first-pass splanchnic metabolism may be responsible for this difference.

Enteral Tryptophan Requirement Determined by Oxidation of Gastrically or Intravenously Infused Phenylalanine Is Not Different from the Parenteral Requirement in Neonatal Piglets

“…However, in each of the present experiments, percentage of dose oxidized was almost as reliable, with model regression coefficients very similar to those for absolute oxidation (Table 2). In previous studies, percentage of dose oxidized provided the most reliable estimates of amino acid requirements, with the lowest error in piglets (3,7,18,23,24) and humans (22,27,29). Using any of the output parameters in Table 2, the break point estimates for enterally fed piglets are well within the CI and SEE for parenterally fed piglets.…”

“…The IAAO technique has been demonstrated previously to be an appropriate method of determining amino acid requirements in enterally and parenterally fed piglets (3,7,23,24). Therefore, the IAAO technique was applied to determine both enteral and parenteral tryptophan requirements for neonatal piglets.…”

“…Therefore, the IAAO technique was applied to determine both enteral and parenteral tryptophan requirements for neonatal piglets. Previously, we have published estimates for parenteral feeding for phenylalanine (18), tyrosine (25), lysine (7), branched-chain amino acids (23), methionine (24), and threonine (3), including an interpretative review of our findings (2). Recently, we have been able to confirm in human infants our piglet findings about parenteral phenylalanine (18) and tyrosine (25) requirements (26,27), which supports our view that the piglet is a good model in which to estimate the amino acid needs of the human neonate (28).…”

“…We have previously demonstrated that the route of diet administration substantially influences the requirements of some indispensable amino acids (3,23,24). For example, the parenteral threonine (3) and methionine (24) requirements have been found to be only 45% and 69% of the respective mean enteral requirements, probably due to the additional roles of these amino acids in gut mucin and glutathione syntheses.…”

Methionine transmethylation and transsulfuration in the piglet gastrointestinal tract

“…Recent studies in neonatal piglets fed cysteine-free diets demonstrated that the whole-body methionine requirement is Ϸ40% lower in total parenterally fed (TPN) compared with enterally fed pigs (31). The difference in this case was attributed to GIT metabolism, because TPN bypasses the gut and results in gut atrophy.…”