Intestinal lysine metabolism is driven by the enteral availability of dietary lysine in piglets fed a bolus meal

Abstract

Intestinal lysine metabolism is driven by the enteral availability of dietary lysine in piglets fed a bolus meal. Am J Physiol Endocrinol Metab 285: E1246-E1257, 2003. First published August 8, 2003 10.1152/ajpendo.00150.2003.-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 non-steady-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 non-steady-state conditions after a single bolus meal. Five 28-day-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 15 N-labeled soy protein and a continuous intravenous infusion of [U-13 C]lysine for 8 h. Total lysine use by the PDV was maximal 1 h after the meal (891 mol ⅐ kg Ϫ1 ⅐ h Ϫ1 ) and was predominantly of dietary origin (89%), paralleling the enteral delivery of dietary lysine. Intestinal lysine use returned to a low level after 4 h postprandially and was derived exclusively from the arterial supply until 8 h. Cumulative systemic appearance of dietary lysine reached 44 and 80% of the ingested amount 4 and 8 h after the meal, respectively, whereas 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 that it is higher with a bolus than with continuous oral feeding.amino acid metabolism; dietary amino acids; portal-drained viscera; nonsteady state STUDIES IN ANIMALS have shown that, during feeding, amino acid utilization by gut tissues is a major determinant of the systemic availability of both essential and nonessential dietary amino acids (27). Indeed, the intestine removes a substantial part of the absorbed dietary essential amino acids to fulfill its own metabolic needs for purposes of protein biosynthesis and energy production (37,39,43,47). This phenomenon can decrease the systemic availability of essential amino acids to the body (39,45,49). However, the gut can also be considered as a buffer, sequestering dietary amino acids through protein synthesis during feeding when they are available in excess, and then releasing them in the fasted state to the peripheral pools when their availability is decreased (12,33).Nonessential amino acids are used by the intestine in synthetic pathways and energy production. They also undergo several metabolic interconversions (in particular, glutamate removal and arginine and alanine synthesis), producing a different pattern of amino acids released in the portal circulation than that of dietary protein (28,29,39,41,43,48).Although the intestine is mainly supplied with dietary ami...

Effects ofdl-2-hydroxy-4-methylthiobutyrate on the first-pass intestinal metabolism of dietary methionine and its extra-intestinal availability

“…These results indicated that, despite the difference in methionine First-pass use of methionine by the intestinesources, the first-pass utilisation of dietary methionine by the intestine remained at about 30 % of intake. Similar results in piglets fed milk protein have been obtained in a previous study (7) , in which dietary methionine intake is about 1·5-fold that in the present study. These results suggested that the fraction of methionine may be more constant than the absolute amount of methionine that is extracted by the intestine in its first-pass.…”

“…From 08.00 to 14.00 hours, pigs were offered meals at hourly intervals, and the meal was the equivalent of one twenty-fourth of the daily intake (45 g/kg BW). Immediately after the first meal, piglets received a constant infusion of [1-13 C]methionine, suspended in water via the gastric catheter at a rate of about 0·25 ml/min to provide [1][2][3][4][5][6][7][8][9][10][11][12][13] C]methionine at 7·0 mmol/kg BW per h. After the tracer infusion was started, the piglets continued to receive hourly meals. Arterial and portal blood samples were taken at hourly intervals until 6 h of tracer infusion, and all the blood samples were immediately placed on ice.…”

Methionine transmethylation and transsulfuration in the piglet gastrointestinal tract

“…The primed, continuous infusion rate was 10 mol⅐kg Ϫ1 ⅐h Ϫ1 for each methionine tracer, so the total isotopic methionine infusion rate was 20 mol⅐kg Ϫ1 ⅐h Ϫ1 . Arterial and portal blood samples were collected at 0, 90, 115, and 120 min and 6, 7, and 8 h. Portal blood f low was monitored continuously by transit-time ultrasound for 30 min before the initial formula feeding and throughout the entire 8-h protocol as described (24,26). After tracer infusion on the second study day, animals were euthanized (Beutanasia-D; Schering-Plough Animal Health, Kenilworth, NJ) and intestinal, pancreas, stomach, and liver tissues were collected and frozen at Ϫ80°C.…”

Intestinal metabolism of sulfur amino acids

“…Other tissues with higher intracellular homocysteine enrichments than in the plasma, including the small intestine, may also contribute to the homocysteinaemia (55) . As regards cysteine in the GIT, studies in pigs indicate that less than 100 % of dietary cysteine appears in the portal blood, suggesting intestinal utilisation of cysteine (47,58) . The first step in cysteine catabolism is its conversion to cysteine sulfinate via the enzyme cysteine dioxygenase (CDO) (Fig.…”