Isotopic analysis of leucine and urea metabolism in exercising humans

Wolfe, Robert R.; Goodenough, Richard D.; Wolfe, M. H.; Royle, G. T.; Nadel, E. R.

doi:10.1152/jappl.1982.52.2.458

Cited by 223 publications

(148 citation statements)

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“…The accurate estimation of FSR of a liver secretory protein requires knowledge of the intrahepatic precursor pool. Such a pool may be indirectly reflected either by the tracer specific activity and enrichment attained in a short-lived hepatic protein at steady state (i.e., in VLDL apolipoprotein B [Apo B] 100) (31) or by other indirect methods, such as KIC labeling in plasma following Leu tracer infusion (32)(33)(34). Indeed, plasma KIC enrichment and specific activity have been shown to be very close to those of VLDL-Apo B 100-bound Leu at steadystate (31,34).…”

Section: Discussionmentioning

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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Section: Discussionmentioning

confidence: 99%

Evidence for Acute Stimulation of Fibrinogen Production by Glucagon in Humans

et al. 1997

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“…Postprandial increases in plasma amino acid levels stimulate protein synthesis, while, during exercise, protein synthesis in skeletal muscle is decreased [13][14][15] and protein degradation is elevated 15) . In addition, endurance exercise increases amino acid oxidation 16) . In general, there are three ways of increasing free amino acid levels in skeletal muscle: (a) degradation of muscle protein; (b) conversion from other amino acids and intermediates; and (c) uptake from extracellular fluid.…”

Section: Amino Acid Pool In Skeletal Musclementioning

confidence: 99%

“…It is generally thought that protein breakdown in humans accounts for increases in essential amino acid levels in muscles during exercise, because essential amino acids are not synthesized de novo. On the other hand, leucine oxidation is known to be elevated during exercise 16) , probably leading to decreases in BCAA levels during exercise as well. We speculate that protein breakdown exceeding amino acid oxidation accounted for the increases in muscle BCAA levels, as demonstrated in the study by Dohm et al 30) .…”

Section: Muscle Fiber Type Differencesmentioning

confidence: 99%

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Exercise-induced changes in amino acid levels in skeletal muscle and plasma

Ishikura¹,

Ra²,

Ohmori³

2013

JPFSM

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During exercise, amino acid oxidation and protein breakdown are enhanced while protein synthesis is suppressed, even though protein does not constitute a quantitatively important energy source. In response to exercise-induced stimulation, various changes in free amino acids occur in skeletal muscle to meet physiological demands. Plasma amino acids are also under the influence of various types of stress, including exercise stress. For example, acute exercise increases alanine and glutamine levels, but decreases glutamate levels in skeletal muscle. At the same time, it increases tryptophan and taurine levels, but decreases glutamine levels in plasma. Prolonged exercise decreases glutamine and glutamate levels, while increasing tyrosine and phenylalanine levels in skeletal muscle. Furthermore, when prolonged exercise-induced changes in amino acid levels are compared between trained and untrained individuals, glutamate and taurine levels in skeletal muscle and phenylalanine, leucine, isoleucine, and tyrosine levels in plasma are higher in trained individuals. This review provides an overview of changes in amino acid levels in skeletal muscle and plasma, with a focus on changes induced by exercise.

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“…On the other hand, leucine oxidation during exercise, *Correspondence: shimo@agr.nagoya-u.ac.jp which can be intensively examined using stable isotopelabeled leucine, was elevated in the early stages of exercise without an increase in urea concentration 10) . These findings suggest that protein breakdown during exercise is underestimated in analyses based on measurement of urea production, and that some amino acids (e.g., leucine) are used as substrates for energy production, even in the early stages of acute exercise.…”

Section: Increased Protein Breakdown By Exercisementioning

confidence: 99%

Effects of protein and amino acid supplementation on muscle protein metabolism in relation to exercise

Shimomura

Kitaura

Shimomura

2012

JPFSM

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Exercise promotes protein and amino acid breakdown in skeletal muscle. Proper nutrient intake in relation to exercise is thus important to maintain or build up skeletal muscle. It has been demonstrated that supplementation of branched-chain amino acids (BCAAs) before exercise has beneficial effects on skeletal muscle, such as decreasing exercise-induced muscle damage and soreness. Protein synthesis in skeletal muscle is enhanced after exercise, and proper timing of supplementation of protein and amino acids for effectively stimulating muscle protein synthesis is herein discussed. Treatment of elderly individuals with exercise and nutrient supplementation is also demonstrated to have efficacy against age-related sarcopenia.

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Isotopic analysis of leucine and urea metabolism in exercising humans

Cited by 223 publications

References 0 publications

Evidence for Acute Stimulation of Fibrinogen Production by Glucagon in Humans

Evidence for Acute Stimulation of Fibrinogen Production by Glucagon in Humans

Exercise-induced changes in amino acid levels in skeletal muscle and plasma

Effects of protein and amino acid supplementation on muscle protein metabolism in relation to exercise

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