|Grusak, Michael - Mike|
|Burrin, Douglas - Doug|
Submitted to: American Journal of Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/7/2003
Publication Date: 8/1/2003
Citation: Bos, C., Stoll, B., Fouillet, H., Gaudichon, C., Guan, X., Grusak, M.A., Reeds, P.J., Tome, D., Burrin, D.G. 2003. Intestinal lysine metabolism is driven by the enteral availability of dietary lysine in piglets fed a bolus meal. American Journal of Physiology. 285:E1246-E1257. Interpretive Summary: The digestion of dietary proteins for growth in young infants is affected by many factors, including the frequency of feeding. The metabolism by the gut is another factor that affects the amount dietary protein absorbed into the blood as amino acids. Lysine is an amino acid found in all protein and is critical for normal growth. Because it is unethical and impractical to determine the gut metabolism of dietary lysine in human infants, we use infant piglets as a model system. Our previous studies with neonatal piglets showed that as much as half of the dietary lysine is metabolized by the gut. However, in this previous study the piglets were fed continuously. Thus, we wanted to know if feeding piglets a bolus meal would alter the amount of dietary lysine metabolized by the gut. We fed young piglets a milk-protein based diet in a single bolus feeding and collected samples of blood. By adding lysine with a special chemical tag, called a stable isotope, to the diet, we were able to see how much of the dietary lysine was metabolized by the gut by measuring the amount of chemically tagged lysine. Consistent with our previous study in continuously fed piglets, we found that approximately half of the dietary lysine was metabolized by the gut during the eight hours after the bolus meal. However, in contrast to our previous study, we found that most of the dietary lysine metabolized by the gut in the eight hour period occurred in the first four hours and was derived mainly from the diet. These studies show that the gut metabolism of lysine increases substantially when more lysine if fed as a bolus rather than continuously fed meal.
Technical Abstract: Previous steady-state, continuous feeding studies have shown that the gut mucosa removes substantial amounts of both dietary and systemic amino acids. However, enteral nutrition is often given under nonsteady-state conditions, as a bolus meal, and this has been shown to influence systemic metabolism. Therefore, our aim was to quantify the relative metabolism of dietary and systemic lysine by the portal-drained viscera (PDV) under nonsteady-state conditions after a single bolus meal. Five 28-d-old piglets implanted with arterial, venous and portal catheters and with an ultrasonic portal flow probe were given an oral bolus feeding of a milk formula containing a trace quantity of intrinsically labeled 15N-soy protein and a continuous i.v. infusion of U-13C-lysine for 8h. Total lysine use by the PDV was maximal 1h after the meal (891 µmol/kg/h) and was predominantly of dietary origin (89%), paralleling the enteral delivery of dietary lysine. Intestinal lysine use returned to a low level after 4h postprandially, and was derived exclusively from the arterial supply until 8h. Cumulative systemic appearance of dietary lysine reached 44% and 80% of the ingested amount 4 and 8h after the meal, respectively, while the PDV first-pass use of dietary lysine was 55% and 32% of the intake for these two periods, respectively. We conclude that the first-pass utilization rate of dietary lysine by the PDV is directly increased by the enteral lysine availability and is higher, with bolus compared to continuous oral feeding.