Threonine utilization is high in the intestine of piglets.
The whole-body threonine requirement in parenterally fed piglets is substantially lower than that in enterally fed piglets, indicating that enteral nutrition induces intestinal processes in demand of threonine. We hypothesized that the percentage of threonine utilization for oxidation and intestinal protein synthesis by the portal-drained viscera (PDV) increases when dietary protein intake is reduced. Piglets (n = 18) received isocaloric normal or protein-restricted diets. After 7 h of enteral feeding, total threonine utilization, incorporation into intestinal tissue, and oxidation by the PDV, were determined with stable isotope methodology [U-(13)C threonine infusion]. Although the absolute amount of systemic and dietary threonine utilized by the PDV was reduced in protein-restricted piglets, the percentage of dietary threonine intake utilized by the PDV did not differ between groups (normal protein 91% vs. low protein 85%). The incorporation of dietary threonine into the proximal jejunum was significantly different compared with the other intestinal segments. Dietary, rather than systemic threonine was preferentially utilized for protein synthesis in the small intestinal mucosa in piglets that consumed the normal protein diet (P < 0.05). Threonine oxidation by the PDV was limited during normal protein feeding. In protein-restricted pigs, half of the total whole-body oxidation occurred in the PDV. We conclude that, in vivo, the PDV have a high obligatory visceral requirement for threonine. The high rate of intestinal threonine utilization is due mainly to incorporation into mucosal proteins.
Schaart
Maaike W
MW
Department of Pediatrics, Division of Neonatology, Erasmus MC/Sophia Children's Hospital, Rotterdam, The Netherlands.
Schierbeek
Henk
H
van der Schoor
Sophie R D
SR
Stoll
Barbara
B
Burrin
Douglas G
DG
Reeds
Peter J
PJ
van Goudoever
Johannes B
JB
D000818:Animals; D002247:Carbon Isotopes; D004750:Enteral Nutrition; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000502:physiology; D011168:Portal System / Q000502:physiology; D013552:Swine; D013912:Threonine / Q000097:blood / Q000378:metabolism*
D002247:Carbon Isotopes; D013912:Threonine