Use of Carbon-14-labelled Arginine to measure the Catabolic Rate of Serum and Liver Proteins and the Extent of Amino-acid Recycling

Stephen, J. M. L.; Waterlow, J. C.

doi:10.1038/211978a0

Cited by 44 publications

(13 citation statements)

References 7 publications

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“…Rates of protein catabolism, as estimated from rates of loss o f 3 H-glutamic acid from various tissues, were not statistically affected by moderate or severe protein or energy restriction. These findings support prior conclusions from this laboratory (14,15) and are contrary to conclusions from other studies (9,10,22,25) in human infants and young and mature rats.…”

contrasting

confidence: 57%

Protein-Energy Interrelationships during Dietary Restriction: Effects on Tissue Nitrogen and Protein Turnover

Nettleton

Hegsted²

1975

Ann Nutr Metab

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Young adult female rats were fed diets containing either 50 or 0 % lactalbumin at levels of 2, 4 or 6 g diet/day for 2, 8, and 16 days. There was no other protein in the diet. Tissue nitrogen and loss of radioactivity from tissues labeled with ¹⁴C- and ³H-glutamate were measured. In a second study, similar rats were fed graded levels of lactalbumin at food intake levels of 3, 5, or 7 g/day. Change in tissue nitrogen varied with the tissue, the time of observation, and the severity of the food restriction. After 8 days, animals fed high levels of protein at the most severe food restriction showed increases in gastrocnemius nitrogen and losses in liver nitrogen, while after 16 days both tissues had marked nitrogen losses. Nitrogen losses at the lowest level of food intake increased with the dietary protein level, whereas dietary protein was protective of tissue nitrogen at higher food intakes. Severity of energy restriction had no effect on loss of tissue radioactivity and the apparently longer tissue protein half-lives from animals fed protein-free diets are attributed to increased amino acid recycling. Such results indicate that short-term studies and overall nitrogen balance experiments will fail to identify changes occurring in different tissues and may yield misleading results.

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confidence: 57%

Protein-Energy Interrelationships during Dietary Restriction: Effects on Tissue Nitrogen and Protein Turnover

Nettleton

Hegsted²

1975

Ann Nutr Metab

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“…When the low protein diet was continued (groups A and C in phase 3), the synthetic rate continued to fall in the recovered children, but was maintained or rose slightly in the malnourished group. The malnourished child may be able to make more efficient use of the reduced supply of amino acids, as a result of adaptive changes associated with increased hepatic amino acid-activating enzymes and increased recycling of amino acids for protein synthesis (46). Extravascular mass.…”

Section: Discussionmentioning

confidence: 99%

Albumin metabolism: effect of the nutritional state and the dietary protein intake

James¹,

Hay²

1968

J. Clin. Invest.

176

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A B S T R A C T Nine malnourished and nine children who had recovered from malnutrition were given a single injection of albumin-131I and were studied during consecutive periods in which the dietary protein was changed.Malnourished children had significantly lower catabolic rates of albumin than had recovered children on the same protein intake. Both nutritional groups, however, showed a progressive fall in catabolic rate after 3-5 days on a low protein diet (0.7-1.0 g/kg per day), and the maximum effect was seen in the 2nd wk of low protein feeding. The catabolic rate could return to normal within 3 wk in a malnourished child fed 4 g of protein/kg per day.The albumin synthetic rate was measured by a computer technique suitable for nonsteady-state conditions. The synthetic rate in the malnourished groups (101 mg/kg per day) fed on a low protein diet was significantly lower than the rate in the recovered groups (148 mg/kg per day). The synthetic rate responded rapidly to a change in diet; when the rate fell, the intravascular albumin mass was maintained by two compensating mechanisms: (1) a net transfer of extravascular albumin into the intravascular pool; and (2) by a delayed fall in the catabolic rate. The net transfer of albumin into the intravascular compartment diminished as the catabolic rate fell.Adaptation to a low protein diet was associated with: (a) low synthetic and catabolic rates of albumin; (b) a reduced extravascular albumin mass;

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“…If the mean half-life of all mixed liver proteins is of the order of 1-2 days as reported in the recent literature (1,3,16,18,19,21), the chances of explaining the changes in liver protein which occur during protein deficiency are very slim. However, the relatively long halflives of 4 -5 days which were observed in these studies must have resulted from killing the animals a considerable time after the injection of the labeled amino acids.…”

Section: Discussionmentioning

confidence: 99%

“…Since it is thought that this amino acid is not normally recycled or re-utilized to any great extent in liver (15,16,19,20), the greater retention observed might be interpreted as a decrease in the rate of catabolism or a stimulation of liver protein synthesis in protein deficient animals (18). However, the feeding of arginine leads to reduced retention of 14C-guanido arginine radioactivity in protein deficient animals but not in normal animals, and hence the apparently greater retention first observed in restricted animals is most likely due to an increase in the rate of recycling of the labeled amino acid rather than to an appreciable change in the metabolic rate.…”

mentioning

confidence: 99%

The Effects of Protein and Calorie Restriction on Tissue Nitrogen Content and Protein Catabolism

Nettleton

Hegsted²

1974

Ann Nutr Metab

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Young adult female rats, previously labeled with L-(¹⁴ C-guanido) arginine and L-(3-³ H) glutamic acid were fed ad libitum diets containing either 10- or 0-percent lactalbumin supplemented with arginine and glutamic acid, 0-percent protein or 10-percent lactalbumin plus amino acids restricted to 5 g diet/ day. Retention of radioactivity in liver and muscle was greater in the restricted groups but was restored to normal by feeding cold amino acid, indicating amino acid recycling. It is concluded that the apparent changes in rates of protein synthesis and degradation during protein and calorie restriction are due to changes in amino acid recycling rather than changes in metabolic rate, and that amino acid reutilization can be minimized by providing dietary amino acids.

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Use of Carbon-14-labelled Arginine to measure the Catabolic Rate of Serum and Liver Proteins and the Extent of Amino-acid Recycling

Cited by 44 publications

References 7 publications

Protein-Energy Interrelationships during Dietary Restriction: Effects on Tissue Nitrogen and Protein Turnover

Protein-Energy Interrelationships during Dietary Restriction: Effects on Tissue Nitrogen and Protein Turnover

Albumin metabolism: effect of the nutritional state and the dietary protein intake

The Effects of Protein and Calorie Restriction on Tissue Nitrogen Content and Protein Catabolism

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