The 24-h kinetics of leucine oxidation in healthy adults receiving a generous leucine intake via three discrete meals

El-Khoury, Antoine E.; Sánchez, Melchor; Fukagawa, Naomi K.; Gleason, Ray E.; Tsay, Rita; Young, Vernon R.

doi:10.1093/ajcn/62.3.579

Cited by 63 publications

(58 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, it is conceivable that bolus feeding upregulates the expression of local growth factors, such as IGF-I, which in turn may increase mucosal lysine utilization for protein synthesis. The other possibility is that the additional lysine used is oxidized, but this is in contrast to studies in humans showing that bolus feeding produces a diminished whole body amino acid oxidation compared with continuous oral feeding (9).…”

Section: Discussionmentioning

confidence: 91%

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

Bos

Stoll²,

Fouillet³

et al. 2003

American Journal of Physiology-Endocrinology and Metabolism

View full text Add to dashboard Cite

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...

show abstract

Section: Discussionmentioning

confidence: 91%

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

Bos

Stoll²,

Fouillet³

et al. 2003

American Journal of Physiology-Endocrinology and Metabolism

View full text Add to dashboard Cite

show abstract

“…15 N]urea, have con®rmed this observation (Hibbert & Jackson, 1991;Carraro et al 1993;el Khoury et al 1994el Khoury et al , 1995bel Khoury et al , 1996Forslund et al 1998). For a summary of work on urea kinetics, see Jackson (1992).…”

Section: The Metabolism Of Ureamentioning

confidence: 82%

The mysteries of nitrogen balance

Waterlow¹

1999

Nutr. Res. Rev.

112

View full text Add to dashboard Cite

The ®rst part of this review is concerned with the balance between N input and output as urinary urea. I start with some observations on classical biochemical studies of the operation of the urea cycle. According to Krebs, the cycle is instantaneous and automatic, as a result of the irreversibility of the ®rst enzyme, carbamoyl-phosphate synthetase 1 (EC 6.3.5.5; CPS-I), and it should be able to handle many times the normal input to the cycle. It is now generally agreed that acetyl glutamate is a necessary co-factor for CPS-1, but not a regulator. There is abundant evidence that changes in dietary protein supply induce coordinated changes in the amounts of all ®ve urea-cycle enzymes. How this coordination is achieved, and why it should be necessary in view of the properties of the cycle mentioned above, is unknown. At the physiological level it is not clear how a change in protein intake is translated into a change of urea cycle activity. It is very unlikely that the signal is an alteration in the plasma concentration either of total amino-N or of any single amino acid. The immediate substrates of the urea cycle are NH 3 and aspartate, but there have been no measurements of their concentration in the liver in relation to urea production. Measurements of urea kinetics have shown that in many cases urea production exceeds N intake, and it is only through transfer of some of the urea produced to the colon, where it is hydrolysed to NH 3 , that it is possible to achieve N balance. It is beginning to look as if this process is regulated, possibly through the operation of recently discovered urea transporters in the kidney and colon. The second part of the review deals with the synthesis and breakdown of protein. The evidence on whole-body protein turnover under a variety of conditions strongly suggests that the components of turnover, including amino acid oxidation, are in¯uenced and perhaps regulated by amino acid supply or amino acid concentration, with insulin playing an important but secondary role. Molecular biology has provided a great deal of information about the complex processes of protein synthesis and breakdown, but so far has nothing to say about how they are coordinated so that in the steady state they are equal. A simple hypothesis is proposed to ®ll this gap, based on the self-evident fact that for two processes to be coordinated they must have some factor in common. This common factor is the amino acid pool, which provides the substrates for synthesis and represents the products of breakdown. The review concludes that although the achievement and maintenance of N balance is a fact of life that we tend to take for granted, there are many features of it that are not understood, principally the control of urea production and excretion to match the intake, and the coordination of protein synthesis and breakdown to maintain a relatively constant lean body mass.

show abstract

“…Two milk protein fractions, CAS and WP, intrinsically labeled with L-[1-and 13 C-CAS for 13 C leucine-intrinsically labeled CAS. Their final leucine enrichments and contents were checked by gas chromatography-mass spectrometry after hydrolysis.…”

Section: Materials L-[1-mentioning

confidence: 99%

“…Studies with ingested labeled proteins and i.v. deuterated leucine ( 13 C-WP and 13 C-CAS studies) allowed us to determine total leucine flux, rate of appearance of exogenous (i.e., dietary) leucine, endogenous leucine production, and exogenous leucine oxidation. Tracers infusion rates, amounts of dietary leucine, and leucine enrichments in the diet are indicated in Table 1.…”

Section: Materials L-[1-mentioning

confidence: 99%

See 1 more Smart Citation

Slow and fast dietary proteins differently modulate postprandial protein accretion

Boirie‌

Dangin

Gachon

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

1,205

999

View full text Add to dashboard Cite

The speed of absorption of dietary amino acids by the gut varies according to the type of ingested dietary protein. This could affect postprandial protein synthesis, breakdown, and deposition. To test this hypothesis, two intrinsically 13 C-leucine-labeled milk proteins, casein (CAS) and whey protein (WP), of different physicochemical properties were ingested as one single meal by healthy adults. Postprandial whole body leucine kinetics were assessed by using a dual tracer methodology. WP induced a dramatic but short increase of plasma amino acids. CAS induced a prolonged plateau of moderate hyperaminoacidemia, probably because of a slow gastric emptying. Whole body protein breakdown was inhibited by 34% after CAS ingestion but not after WP ingestion. Postprandial protein synthesis was stimulated by 68% with the WP meal and to a lesser extent (؉31%) with the CAS meal. Postprandial whole body leucine oxidation over 7 h was lower with CAS (272 ؎ 91 mol⅐kg ؊1 ) than with WP (373 ؎ 56 mol⅐kg ؊1 ). Leucine intake was identical in both meals (380 mol⅐kg ؊1 ). Therefore, net leucine balance over the 7 h after the meal was more positive with CAS than with WP (P < 0.05, WP vs. CAS). In conclusion, the speed of protein digestion and amino acid absorption from the gut has a major effect on whole body protein anabolism after one single meal. By analogy with carbohydrate metabolism, slow and fast proteins modulate the postprandial metabolic response, a concept to be applied to wasting situations.

show abstract

The 24-h kinetics of leucine oxidation in healthy adults receiving a generous leucine intake via three discrete meals

Cited by 63 publications

References 21 publications

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

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

The mysteries of nitrogen balance

Slow and fast dietary proteins differently modulate postprandial protein accretion

Contact Info

Product

Resources

About