Tissue-Specific Mass Changes During Fasting: The Protein Turnover Hypothesis

Bauchinger, Ulf; McWilliams, Scott R.

doi:10.1007/978-3-642-29056-5_12

Cited by 18 publications

(19 citation statements)

References 55 publications

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“…large intestine, and oviduct) whereas the tissues with the slowest rates of protein turnover were the brain, heart, lung, and blood cells. The relative rates of tissue-specific protein turnover suggested by these data closely parallel those reported for non-galliform birds (reviewed in Bauchinger & McWilliams, 2012). Only the lean fraction of the skin and the adipocytes had ratios less than 1.0.…”

supporting

confidence: 81%

Hens Produce Artificially Enriched 13C Egg Proteins for Metabolic Tracer Studies

McCue

Arquisola²,

Albach³

et al. 2013

IJB

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Clinicians and researchers studying protein metabolism in vivo, typically use isotopically-labeled free amino acids as metabolic tracers rather than isotopically-labeled proteins because such proteins are commercially unavailable. However, the use of free amino acids in lieu of protein tracers violates the critical assumption that tracer molecules undergo the identical biochemical reactions as the tracee molecules of interest. To address this problem we synthesized 13 C-labeled proteins using egg laying hens and investigated the relationship between tracer dose and method of delivery on 13 C-protein production. We enriched hens with one of two isotope tracers ( 13 C-1-leucine or a uniformly labeled 13 C-amino acid mixture) mixed in their food or dissolved in their drinking water at different dosing levels (86-432 mg day -1 ). The recovery of 13 C in egg white proteins of the hen fed 13 C-leucine ranged from 14% to 21%; recovery rates were highest at the lowest dosing level. At the highest dosing level egg whites were enriched more than 150‰ above background levels of 13 C. The time required for half maximal 13 C enrichment depended chiefly on the mode of tracer administration, and ranged from 2.5 days for 13 C-leucine dissolved in water to 4.9 days for 13 C-leucine mixed in food. Relative rates of 13 C recovery in the egg protein were lowest for hens fed the uniformly 13 C labeled amino acid mixture, presumably because of the high proportion of nonessential amino acids. The time required for the 13 C-enrichment in eggs to return to background levels at the end of the enrichment period was about twice that required to initially reach isotopic equilibrium with the diet, indicating significant biochemical discrimination of endogenous 13 C amino acids. We conclude that delivering small amounts of 13 C amino acid tracers in the drinking water of hens is the most effective way to produce 13 C-enriched proteins to for tracer studies that do not require δ 13 C-enrichment above 200‰.

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supporting

confidence: 81%

Hens Produce Artificially Enriched 13C Egg Proteins for Metabolic Tracer Studies

McCue

Arquisola²,

Albach³

et al. 2013

IJB

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“…However, turnover time could be more than double if calculated using the annual average water temperature (c. 4°C), which could further explain why annual differences in terrestrial reliance were not apparent in muscle tissues. Several studies agree that splanchnic tissues (such as liver) should turnover at a faster rate than structural tissues (such as muscle), though rates in the former cannot be as easily calculated as turnover in muscle, since the exact rate depends on species-specific metabolism (Reich, Bjorndal & Del Rio, 2008;Bauchinger & McWilliams, 2012;Thomas & Crowther, 2015). However, no annual differences were found in terrestrial reliance derived from the liver tissue or ingested diet, lending further support to the hypothesis that terrestrial subsidies to the higher levels of the food web might be a constant feature in the long term.…”

Section: Discussionmentioning

confidence: 99%

Reliance of brown trout on terrestrial prey varies with season but not fish density

2016

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Summary The importance of terrestrial carbon in aquatic ecosystems is widely recognised, but patterns of terrestrial reliance can be variable. Fish often act as important links between terrestrial and aquatic ecosystems, but little is known about how resource seasonality and fish density influence fish reliance on terrestrial energy in lakes. We sampled a high‐latitude subarctic lake in Finnish Lapland during the open‐water season over three consecutive years to assess both patterns of terrestrial reliance and trophic niche structure of introduced brown trout (Salmo trutta), the only resident fish species. The small size of the study lake made it possible to sample the whole population by conducting a complete fish removal, allowing for a direct assessment of size structure and changes in brown trout density over time. We hypothesised that annual and seasonal shifts in the dietary niches of brown trout would directly track the availability of pulsed resources such as aquatic and terrestrial insects as well as rodents. We further expected that dietary niche shifts would be correlated with population density, leading to a smaller trophic niche size at lower densities. We therefore investigated the annual and seasonal patterns of resource use using measures of dietary niche and in particular of terrestrial reliance, derived from stomach content analysis and stable‐isotope analyses (SIA) of liver and muscle, along a temporal gradient of declining fish density. According to stomach content, terrestrial reliance in brown trout was the highest in each year at mid‐to‐late summer, evidently following the peak abundance of terrestrial invertebrates and rodents. Surprisingly, we could not detect annual or seasonal shifts in terrestrial reliance from estimates provided by isotope ratios in muscle or liver. Furthermore, fish density did not appear to influence either terrestrial reliance or trophic niche size. However, trophic position derived from SIA of liver tissue decreased with decreasing densities, while fish condition increased. Large, consistent pulses of terrestrial invertebrates in mid‐summer (or rodents during their peak years) are likely important for brown trout in the long term and could explain the lack of density‐dependent correlation in terrestrial reliance. However, further studies are needed to link the abundance of pulsed resources to resource use by fish across wider gradients of lake size, productivity and fish density.

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“…If energy metabolism does not explain the variation in turnover rate within a tissue, as discussed above, it seems also unlikely that energy expenditure explains variation between tissues within individuals. The few studies that have measured turnover rate in a variety of tissues confirm that turnover rate differences between tissues cannot be explained by variation in the energy expenditure of these tissues [72,73]. Splanchic organs like the liver and small intestine appear to have fast rates of isotopic incorporation, while muscles have slow rates and internal organs like the gizzard, kidney and heart arrange themselves in between.…”

Section: The Physiological Basis Of Isotopic Clocks: Variation In Turmentioning

confidence: 99%

“…It appears that some tissues like the brain, bone and skin pose some issues in that they are either extremely slow in turnover rates and thus do not reach asymptotes in the respective studies, or the lack of fit is a result of large variation in the determinant of the isotopic incorporation [55,69]. Protein synthesis and degradation of the respective organ more likely determine the rate of isotopic incorporation than the simple energy turnover of the respective organ, as demonstrated through dietary manipulations (see above and [57,58,73]). Also, the study that employed manipulations of energy budget through both temperature manipulation and the manipulation of flight exercise with the goal to test for predicted associations between energy use and isotopic turnover (see section just above) sampled not only the blood but a variety of organs [55].…”

Section: The Physiological Basis Of Isotopic Clocks: Variation In Turmentioning

confidence: 99%

The Importance of Isotopic Turnover for Understanding Key Aspects of Animal Ecology and Nutrition

2019

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Stable isotope-based methods have proved to be immensely valuable for ecological studies ranging in focus from animal movements to species interactions and community structure. Nevertheless, the use of these methods is dependent on assumptions about the incorporation and turnover of isotopes within animal tissues, which are oftentimes not explicitly acknowledged and vetted. Thus, the purpose of this review is to provide an overview of the estimation of stable isotope turnover rates in animals, and to highlight the importance of these estimates for ecological studies in terrestrial, freshwater, and marine systems that may use a wide range of stable isotopes. Specifically, we discuss 1) the factors that contribute to variation in turnover among individuals and across species, which influences the use of stable isotopes for diet reconstructions, 2) the differences in turnover among tissues that underlie so-called ‘isotopic clocks’, which are used to estimate the timing of dietary shifts, and 3) the use of turnover rates to estimate nutritional requirements and reconstruct histories of nutritional stress from tissue isotope signatures. As we discuss these topics, we highlight recent works that have effectively used estimates of turnover to design and execute informative ecological studies. Our concluding remarks suggest several steps that will improve our understanding of isotopic turnover and support its integration into a wider range of ecological studies.

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Tissue-Specific Mass Changes During Fasting: The Protein Turnover Hypothesis

Cited by 18 publications

References 55 publications

Hens Produce Artificially Enriched 13C Egg Proteins for Metabolic Tracer Studies

Hens Produce Artificially Enriched 13C Egg Proteins for Metabolic Tracer Studies

Reliance of brown trout on terrestrial prey varies with season but not fish density

The Importance of Isotopic Turnover for Understanding Key Aspects of Animal Ecology and Nutrition

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