Tracers To Investigate Protein And Amino Acid Metabolism In Human Subjects PdfBy Comforte S. In and pdf 19.04.2021 at 09:58 5 min read
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- Protein and Amino Acid Metabolism in Human Muscle
- Tracers to investigate protein and amino acid metabolism in human subjects.
- Critical Assessment of Methods Used to Measure Protein Synthesis In Human Subjects
Protein turnover in skeletal muscle tissue is highly responsive to nutrient intake in healthy adults. To provide a comprehensive overview of post-prandial protein handling, ranging from dietary protein digestion and amino acid absorption, the uptake of dietary protein derived amino acids over the leg, the post-prandial stimulation of muscle protein synthesis rates, to the incorporation of dietary protein derived amino acids in de novo muscle protein. In addition, primed continuous L-[ring- 2 H 5 ]-phenylalanine, L-[ring- 2 H 2 ]-tyrosine, and L-[1- 13 C]-leucine infusions were applied, with frequent collection of arterial and venous blood samples, and muscle biopsies throughout a 5 h post-prandial period.
Protein and Amino Acid Metabolism in Human Muscle
Muscle proteins turn over slowly and there are minimal diurnal changes in the size of the muscle protein pool in response to feeding and fasting. An imbalance between muscle protein synthesis and degradation does exist during one leg knee extensor exercise and during two legged cycling in patients with glycogen Phosphorylase deficiency. In these latter cases amino acids liberated from the protein pool are used for synthesis of TCA-cycle intermediates and glutamine. Unable to display preview. Download preview PDF. Skip to main content.
Tracers to investigate protein and amino acid metabolism in human subjects.
The ingestion of intact protein or essential amino acids EAA stimulates mechanistic target of rapamycin complex-1 mTORC1 signaling and muscle protein synthesis MPS following resistance exercise. Ten young Myofibrillar-MPS was measured during exercise recovery with a primed, constant infusion of L-[ring 13 C 6 ] phenylalanine and collection of muscle biopsies pre and 4 h-post drink ingestion. Blood samples were collected at time-points before and after drink ingestion. Western blotting was used to measure the phosphorylation status of mTORC1 signaling proteins in biopsies collected pre, 1-, and 4 h-post drink. It is well-established that ingestion of essential amino acids EAA following resistance exercise stimulates an increased response of muscle protein synthesis MPS in humans Smith et al.
Regulation of glucose homeostasis by insulin is modified during aging, but whether this alteration is associated with changes in protein metabolism is less defined. Insulin dose responses of whole body glucose, leucine, and albumin metabolism have been investigated using isotopic dilution of d -[6, 6- 2 H 2 ]glucose and l -[1- 13 C]leucine in 14 young Y; Despite significantly higher plasma insulin in E than in Y, the glucose disposal rate was lower in E than in Y at both insulin levels, whereas glucose production was normally suppressed. The albumin synthesis rate was identical and stimulated to the same extent by insulin in groups Y and E. Gender affected basal leucine metabolism, but the response to insulin was similar in both groups. In conclusion, decreased insulin action on glucose disposal is associated with a reduced insulin sensitivity for protein breakdown in healthy elderly subjects at low insulin concentrations. Higher insulin levels compensate for a reduced insulin action on protein metabolism in elderly subjects.
Critical Assessment of Methods Used to Measure Protein Synthesis In Human Subjects
John's Research Institute, Bengaluru, India. Indians have a poor protein intake in terms of quantity as well as quality because of their predominantly cereal-based diet. However, there is limited information on circulatory amino acid levels in healthy Indians. Herein, we evaluated the acute effect of a protein supplement on the plasma levels of essential amino acids EAAs in healthy Indian adults, using targeted EAA analysis.
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Protein depletion is a major determinant of clinical outcome in a number of catabolic states. Hence, assessment of protein metabolism is necessary to understand these conditions as well as to evaluate treatment. Since the regulation of synthesis and breakdown of proteins differs between tissues, it is preferable to study the parameters of protein metabolism separately, and at the organ level. In this chapter we will discuss techniques developed to study liver protein metabolism in man.
The investigation of protein metabolism under various nutritional and physiological conditions has been made possible by the use of indirect, principally tracer-based methods. Most studies were conducted at the whole-body level, mainly using steady-state isotopic techniques and equations based on simple two-pool models, in which amino acids are either free or protein bound. Because whole-body methods disregard regional contributions to protein metabolism, some regional approaches have tried to distinguish the distribution of protein kinetics in the different tissues. The organ-balance tracer technique, involving the arteriovenous catheterization of regions or organs with concomitant isotopic tracer infusion, distinguishes between amino acid uptake and release in the net amino acid balance and measures protein synthesis and degradation under steady-state conditions. Last, the importance has become clear of the difference in dietary and endogenous amino acids recycled from proteolysis for anabolic and catabolic pathways. Furthermore, the whole-body retention of labeled dietary nitrogen after the ingestion of a single protein meal has enabled a clearer understanding of the metabolic fate of dietary amino acids. Based on such data, a newly developed compartmental model provides a simulation of the regional distribution and metabolism of ingested nitrogen in the fed state by determining its dynamic fate through free and protein-bound amino acids in both the splanchnic and peripheral areas in humans.
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