Rapid measurement of whole body and forearm protein turnover using a [2H5]phenylalanine model

Thompson, G. N.; Pacy, P. J.; Merritt, H. Houston; Ford, G. C.; Read, M.; Cheng, K. N.; Halliday, D.

doi:10.1152/ajpendo.1989.256.5.e631

Cited by 126 publications

(150 citation statements)

References 29 publications

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“…Whole-body incorporation of phenylalanine into protein is calculated by subtracting I PT from Q Phe because apart from conversion to tyrosine the only other fate of phenylanine is protein synthesis. The basis of these equations is discussed elsewhere [3,21].…”

Section: Calculationsmentioning

confidence: 99%

Renal amino acid, fat and glucose metabolism in type 1 diabetic and non-diabetic humans: effects of acute insulin withdrawal

et al. 2006

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Aims/hypothesis: The aim of this study was to test the hypothesis that type 1 diabetes alters renal amino acid, glucose and fatty acid metabolism. Materials and methods: We studied five C-peptide-negative, type 1 diabetic subjects during insulin replacement (glucose 5.6 mmol/l) and insulin deprivation (glucose 15.5 mmol/l) and compared them with six non-diabetic subjects. Leucine, phenylalanine, tyrosine, glucose and palmitate tracers were infused after an overnight fast and samples were obtained from the renal vein, femoral vein and femoral artery. Results: Insulin deprivation significantly increased wholebody fluxes (20-25%) of phenylalanine, tyrosine and leucine, and leucine oxidation (50%). Kidney contributed 5-10% to the whole-body leucine and phenylalanine flux. A net uptake of phenylalanine, conversion of phenylalanine to tyrosine (5 μmol/min) and net release of tyrosine (∼5 μmol/min) occurred across the kidney. Whole-body (three-fold) and leg (two-fold) leucine transamination increased but amino acid metabolism in the kidney did not alter with diabetes or insulin deprivation. Insulin deprivation doubled endogenous glucose production, renal glucose production was unaltered by insulin deprivation and diabetes (ranging between 100 and 140 μmol/min).Renal palmitate exchange was unaltered by insulin deprivation. Conclusions/interpretation: In conclusion, kidney postabsorptively accounts for 5-10% of whole-body protein turnover, 15-20% of leucine transamination and 10-15% of endogenous glucose production, and actively converts phenylalanine to tyrosine. During insulin deprivation, leg becomes a major site for leucine transamination but insulin deprivation does not affect renal phenylalanine, leucine, palmitate or glucose metabolism. Despite its key metabolic role, insulin deprivation in type 1 diabetic patients does not alter many of these metabolic functions.

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Section: Calculationsmentioning

confidence: 99%

Renal amino acid, fat and glucose metabolism in type 1 diabetic and non-diabetic humans: effects of acute insulin withdrawal

et al. 2006

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“…The first step in the oxidation of phenylalanine is hydroxylation in the liver to tyrosine. The rate of oxidation, therefore, can be quantified from the enrichment of L-[ 2 H 4 ]tyrosine at steady-state (for exact details of the assumptions behind the method and calculations, see Thompson et al 1989). In a modification of this method (for example, see Marchini et al 1993) a second tyrosine tracer (L-[ 2 H 2 ]tyrosine) is infused in order to measure total tyrosine Ra in arterial plasma, analogous to the measurement of total CO 2 production in the leucine method.…”

Section: Whole-body Protein Turnovermentioning

confidence: 99%

Tracers to investigate protein and amino acid metabolism in human subjects

Wagenmakers

1999

Proc. Nutr. Soc.

110

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Abbreviations: FSR, fractional synthesis rate; IRMS, isotope-ratio mass spectrometry; α-KIC, α-ketoisocaproic acid; MS, mass spectrometry; nb, net balance of tracer; NB, net balance of tracee; Ra, rate of appearance; Rd, rate of disappearance. The contribution of whole-body methods to the future gain of knowledge is expected to be limited due to the fact that most physiological disturbances have been investigated extensively, and due to the lack of information on the relative contribution of various tissues and proteins to whole-body changes.Tracer amino acid-incorporation methods are most suited to investigate these latter aspects of protein metabolism. These methods have shown that some tissues (liver and gut) have much higher turnover rates and deposit much more protein than others (muscle). Massive differences also exist between the fractional synthesis rates of individual proteins. The incorporation methods have been properly validated, although minor disagreements remain on the identity of the true precursor pool (the enrichment of which should be used in the calculations). Arterio-venous organ balance studies have shown that little protein is deposited in skeletal muscle following a proteincontaining meal, while much more protein is deposited in liver and gut. The amount deposited in the feeding period in each of these tissues is released again during overnight fasting. The addition of tracers to organ balance studies allows the simultaneous estimation of protein synthesis and protein breakdown, and provides information on whether changes in net protein balance are caused primarily by a change in protein synthesis or in protein breakdown. In the case of a small arterio-venous difference in a tissue with a high blood flow, estimates of protein synthesis and breakdown become very uncertain, limiting the value of using the tracer. An additional measurement of the intracellular free amino acid pool enrichment allows a correction for amino acid recycling and quantification of the inward and outward transmembrane transport. However, in order to obtain reliable estimates of the intramuscular amino acid enrichment and, therefore, of muscle protein synthesis and breakdown in this so-called three-pool model, the muscle should be freeze-dried and the resulting fibres should be freed from connective tissue and small blood clots under a dissection microscope. Even when optimal precautions are taken, the calculations in these tracer balance methods use multiple variables and, therefore, are bound to lead to more variability in estimates of protein synthesis than the tracer amino acid incorporation methods. In the future, most studies should focus on the measurement of protein synthesis and breakdown in specific proteins in order to understand the mechanisms behind tissue adaptation in response to various stimuli (feeding, fasting, exercise, trauma, sepsis, disuse and disease). The tracer laboratories, therefore, should improve the methodology to allow the measurement of low tracer amino acid enrichments in small amount...

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“…The third calculation was performed with the aim of correcting FSR for another estimate of intracellular (i.e., intrahepatic) Phe specific activity, i.e., Phe-derived Tyr specific activity in plasma. Obviously, such a calculation yields only qualitative information, since plasma Tyr specific activity cannot be used to estimate intracellular Phe specific activity in the liver or, therefore, absolute values of fibrinogen FSR for the following reasons: 1) Only -15-20% of plasma Tyr derives from hydroxylation of Phe (19,20), the majority of its flux being accounted for by proteolysis. 2) Dilution of plasma [ 14 C]Tyr specific activity reflects proteolysis occurring almost everywhere in body tissues, while Phe hydroxylation into Tyr should take place almost exclusively in liver (21).…”

Section: Ptessari and Associatesmentioning

confidence: 99%

Evidence for Acute Stimulation of Fibrinogen Production by Glucagon in Humans

et al. 1997

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Fibrinogen, an acute-phase protein, and glucagon, a stress hormone, are often elevated in many conditions of physical and metabolic stress, including uncontrolled diabetes. However, the possible mechanisms for this association are poorly known. We have studied the acute effects of selective hyperglucagonemia (raised from -200 to -350 pg/ml for 3 h) on fibrinogen fractional secretion rate (FSR) in eight normal subjects during infusion of somatostatin and replacement doses of insulin, glucagon, and growth hormone. Fibrinogen FSR was evaluated by precursor-product relationships using either Phe (n = 8) or Leu (« = 2) tracers. Hyperglucagonemia did not change either plasma Phe or Tyr specific activity. After hyperglucagonemia, fibrinogen FSR increased by -65% (from 12.9 ± 3.6 to 21.5 ± 6.1% per day, P < 0.025) using plasma Phe specific activity as the precursor pool. FSR increased by -80% (from 16.6 ± 4.8 to 29.4 ± 8.8% per day, P < 0.025) if plasma Phe specific activity was corrected for the ketoisocaproate/Leu enrichment (or specific activity) ratio to obtain an approximate estimate of intrahepatic Phe specific activity. FSR increased by -60% when using plasma Tyr specific activity as precursor pool (n = 8) (P < 0.05), as well as when using the Leu tracer precursorproduct relationship (n = 2). In conclusion, selective hyperglucagonemia for -3 h acutely stimulated fibrinogen FSR using a Phe tracer method. Thus, glucagon may be involved in the increase of fibrinogen concentration and FSR observed under stressed or pathologic conditions. Diabetes 46:1368-1371, 1997 F ibrinogen is an acute-phase protein (1) that is increased in uncontrolled diabetes, vascular disease, and smoking and in many conditions of physical and metabolic stress (2-6). Its plasma concentration has been recognized as a strong and independent cardiovascular risk factor (7). Nevertheless, the mechanisms and the factors that regulate fibrinogen synthesis in vivo are poorly understood. In humans, fibrinogen fractional secretion rate (FSR) was increased by acute insulin deficiency in IDDM (8), while it was decreased by short-term insulin infusion in both normal subjects and subjects with IDDM (8,9). Received for publication 10 December 1996 and accepted in revised form 12 May 1997.FSR, fractional secretion rate; HPLC, high-performance liquid chromatography; KIC, a-ketoisocaproate; MPE, mole percent enrichment.Besides these scarce data, however, the role of other hormonal or metabolic factors in regulating fibrinogen FSR in vivo is largely unknown. In many conditions in which fibrinogen concentration is elevated, including uncontrolled diabetes (10), the concentration of glucagon is also increased. Since glucagon is a stress hormone (11), it might be involved in the synthesis of acute-phase reactants. Thus, it is interesting to investigate whether there is a causal association between increments of glucagon concentrations and fibrinogen FSR in vivo.The aim of this study was therefore to evaluate whether an isolated and acute increase of glucagon concen...

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Rapid measurement of whole body and forearm protein turnover using a [2H5]phenylalanine model

Cited by 126 publications

References 29 publications

Renal amino acid, fat and glucose metabolism in type 1 diabetic and non-diabetic humans: effects of acute insulin withdrawal

Renal amino acid, fat and glucose metabolism in type 1 diabetic and non-diabetic humans: effects of acute insulin withdrawal

Tracers to investigate protein and amino acid metabolism in human subjects

Evidence for Acute Stimulation of Fibrinogen Production by Glucagon in Humans

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