|VAN DER SCHOOR, SOPHIE|
|Burrin, Douglas - Doug|
|VAN GOUDOEVER, JOHANNES|
Submitted to: Gastroenterology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2002
Publication Date: 12/1/2002
Citation: VAN DER SCHOOR, S.D., REEDS, P.J., STOLL, B., HENRY, J.F., ROSENBERGER, J.R., BURRIN, D.G., VAN GOUDOEVER, J.B. THE HIGH METABOLIC COSTS OF A FUNCTIONAL GUT. GASTROENTEROLOGY. Gastroenterology. 2002.v. 123. p. 1931-1940.
Interpretive Summary: The digestion and absorption of dietary proteins for growth in young infants is critical for normal growth, especially those born preterm. Even though most proteins fed to newborn infants are highly digestible, the amount of amino acids absorbed into the blood stream is affected by gut metabolism. Because the gut is so metabolically active, it consumes much of the dietary protein intake just to meet the needs for normal growth and development. Because it is unethical and impractical to determine the gut metabolism of dietary amino acids in human infants, we use infant piglets as a model system. Our previous studies with neonatal piglets showed that as much as a third to half of the dietary amino acid intake is metabolized by the gut. An important unresolved question however, was to what extent the gut releases amino acids into the blood stream when digestion and absorption of a meal is completed. We tested this by measuring the quantity of amino acids absorbed into the blood stream while the infant piglets were fed continuously for 12 hours and then during the 12 hours when they were not fed anything. Like our previous studies, we found that a large proportion (60-75%) of the dietary amino acids were taken up and metabolized by the gut during the 12 hours of feeding. However, in the 12 hour period while the pigs were not fed, nearly one third of the amino acid taken up by the gut during feeding were released back into the blood stream. This process of gut recycling of dietary amino acids contributes significantly to their availability for infant growth and may be a critical factor in amino acid nutrition.
Technical Abstract: Background & Aims: Animal studies have shown that more than half of the dietary protein intake is used by the gut and that a large proportion of this utilization is devoted to (glyco-)protein synthesis. Recycling of these secretions may play a critical role in the regulation of overall dietary amino acid bioavailability. Methods: Four piglets (age 32 days, 8-10 kg) bearing portal, arterial, and duodenal catheters and a portal flow probe were infused with a complete diet via the duodenum for 12 hours, followed by 12 hours of fasting. The portal balance of glucose and amino acids was measured throughout the 24-hour period. The animals also received duodenal and intravenous infusions of different lysine and threonine tracers. Measurements of intestinal tracer utilization and reappearance in the portal blood were used to calculate intestinal amino acid utilization and recycling. Results: From 0 to 6 hours, one third of the protein intake appeared in the portal blood. As feeding continued, the portal glucose balance (60% of intake) was constant, but the net amino acid portal balance became progressively more positive. Significant net amino acid absorption continued for at least 6 hours after the cessation of feeding. Over 24 hours, 52% of the dietary protein intake appeared in the circulation and one third of this derived from recycled intestinal secretions. Conclusions: Intestinal recycling of amino acids contributes significantly to their systemic availability and may be a critical factor in amino acid nutrition.