|Grusak, Michael - Mike|
|Burrin, Douglas - Doug|
Submitted to: American Journal of Physiology - Endocrinology and Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2004
Publication Date: 2/1/2005
Citation: Bos, C., Stoll, B., Fouillet, H., Gaudichon, C., Guan, X., Grusak, M.A., Reeds, P.J., Burrin, D.G., Tome, D. 2005. Postprandial intestinal and whole body nitrogen kinetics and distribution in piglets fed a single meal. American Journal of Physiology: Endocrinology and Metabolism. 288(2):E436-E446. Interpretive Summary: Infants have a relative high dietary protein requirement for normal growth, development and function compared to adults. The dietary protein consumed by infants is digested into amino acids, which are then absorbed into the body and used for muscle and organ growth. Our previous studies with baby piglets suggest that a large proportion of the dietary protein ingested is broken down to amino acids, which are used for growth and important functions in the gut. The use of dietary protein by the gut reduces the amount left for growth of body tissues, such as muscle. Amino acids are broken down in the gut to a variety of end-products, some of which are useful, whereas others are excreted from the body as waste, namely urea. Using the baby pig as a model for the human infant, we conducted a study to determine how much of the dietary protein intake is absorbed from the gut and used for growth of body tissues, such as muscle. In order to track the dietary protein through the processes of digestion, absorption and uptake into body proteins, we fed the pigs a soy protein labeled with stable nitrogen isotopes. We found that only about 5% of the dietary protein was lost from the body as the waste-product urea. We also found that 20% of dietary protein was used by the gut and liver, whereas nearly 50% was used by the muscle and skin. Another important finding was that a portion of the dietary protein appears to be absorbed from the gut as small fragments of protein rather than amino acids.
Technical Abstract: Our aim was to characterize the postprandial total and dietary N fluxes in the portal drained- viscera (PDV) and whole-body after administration of a single meal in young pigs. Seven 4-wk old piglets, implanted with a portal flow probe and portal, arterial and venous catheters, received a primed constant **18**O-urea i.v. infusion and were studied for 8h after a bolus mixed meal ingestion (46 mmolN/kgBW) intrinsically labeled with **15**N to trace dietary N fluxes. The real cecal digestibility of the formula was 94.3±1.8%. PDV output of dietary N was principally found in the pool of circulating protein (51% of the measured dietary N PDV output), in the free alpha-amino N pool (44%), and to a lesser extent in ammonia (5%). Dietary N release in alpha-amino N and ammonia mainly occurred during the first 3h. Total and exogenous postprandial urea productions were 5.8 and 2.0 mmolN/kgBW, respectively. At the end of the postprandial period, losses of dietary N amounted to 10.3% of the dose: 5.7% through ileal losses and 4.6% by deamination and transfer to urea. The net postprandial retention of dietary N was 90.4±1.3%, out of which 20% was found in splanchnic zone (small intestine: 10%, liver: 5% and plasma protein: 3%) and 42% in peripheral zone (muscle: 31%, skin: 6%). In conclusion, our results show a high efficiency of dietary N utilization for muscular uptake and anabolic utilization. However, the results obtained point out the necessity to further explore the form of dietary N released into the portal blood.