Protein Metabolism in Human Neonates: Nitrogen-Balance Studies, Estimated Obligatory Losses of Nitrogen and Whole-Body Turnover of Nitrogen

1977 ◽  
Vol 52 (5) ◽  
pp. 485-498 ◽  
Author(s):  
P. B. Pencharz ◽  
W. P. Steffee ◽  
W. Cochran ◽  
N. S. Scrimshaw ◽  
W. M. Rand ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Nitrogen Balance ◽  
Growth And Development ◽  
Term Infant ◽  
Nitrogen Losses ◽  
Whole Body ◽  
Nitrogen Flux ◽  
Body Protein ◽  
Mean Values ◽  
The Mean

1. Aspects of nitrogen metabolism in the human neonate were assessed in one full-term infant and six premature infants by means of nitrogen-balance measurements, estimates of obligatory nitrogen losses and determinations of whole-body nitrogen turnover. 2. Our data indicate that the mean protein requirement for maintenance is 1·1 g of protein day−1 kg−1 and that 3·8 g of protein day−1 kg−1 should be sufficient for adequate growth in healthy premature babies. 3. The mean obligatory urinary, faecal and total nitrogen losses were estimated to be 24, 106 and 145 mg day−1 kg−1 respectively. These figures are compared with published values for older infants, and the possible metabolic basis for changes in nitrogen losses during growth and development is discussed. 4. Mean values for whole-body protein synthesis and breakdown were 26·3 ± 7·0 and 23·8 ± 7·4 g of protein day−1 kg−1 respectively. Dietary nitrogen intake accounted for 6–18% of the nitrogen flux through the metabolic pool; urea excretion accounted for 2% of the nitrogen flux. 5. The net protein gain, estimated from nitrogen-balance data, accounted for 9·6% of total daily protein synthesis. 6. These results are discussed in relation to published estimates of whole-body protein synthesis and breakdown at various ages. Their possible significance in the assessment of a ‘maintenance’ requirement for protein and amino acids during the period of rapid growth and development is also considered.

Whole-Body Protein Turnover before and after Resection of Colorectal Tumours

1983 ◽  
Vol 64 (1) ◽  
pp. 101-108 ◽  
Author(s):  
R. E. Glass ◽  
E. B. Fern ◽  
P. J. Garlick
Keyword(s):  
Protein Synthesis ◽  
Primary Tumour ◽  
Experimental Period ◽  
Whole Body ◽  
Tumour Resection ◽  
Surgical Removal ◽  
Protein Breakdown ◽  
Nitrogen Flux ◽  
Body Protein ◽  
Before And After

1. The rate of whole-body nitrogen flux; protein synthesis and protein breakdown were measured in patients with colorectal cancer (Dukes A—C) just before and 12 weeks after surgical removal of the tumour. The rates were determined from the urinary excretion of 15N in ammonia and in urea over a 9 h period after an oral dose of [15N]glycine. 2. The food intake during the 2 study days was identical for individual patients. The amount each received was determined from measurement of their intake of food ad libitum on the day preceding the pre-operative study and was consumed in six equal portions every 2 h during the experimental period. 3. No significant differences in the rates of nitrogen flux, protein synthesis and protein breakdown were found before and after tumour resection, whether calculated from the excretion of 15N in ammonia or in urea. Some changes in flux, both increases and decreases, were observed in individual patients after tumour removal but these could not be related to classification of the tumour, or to the presence of pre-operative anorexia or weight loss. 4. The results suggest that the primary tumour itself does not alter the overall rate of protein metabolism in the whole body.

Effect of spaceflight on human protein metabolism

1993 ◽  
Vol 264 (5) ◽  
pp. E824-E828 ◽  
Author(s):  
T. P. Stein ◽  
M. J. Leskiw ◽  
M. D. Schluter
Keyword(s):  
Protein Synthesis ◽  
Nitrogen Balance ◽  
Protein Metabolism ◽  
Space Shuttle ◽  
Single Pulse ◽  
Whole Body ◽  
Synthesis Rate ◽  
Protein Synthesis Rate ◽  
Body Protein ◽  
Space Shuttle Columbia

Nitrogen balance and the whole body protein synthesis rate were measured before, during, and after a 9.5-day spaceflight mission on the space shuttle Columbia. Protein synthesis was measured by the single-pulse [15N]glycine method. Determinations were made 56, 26, and 18 days preflight, on flight days 2 and 8, and on days 0, 6, 14, and 45 postflight. We conclude that nitrogen balance was decreased during spaceflight. The decrease in nitrogen balance was greatest on the 1st day when food intake was reduced and again toward the end of the mission. An approximately 30% increase in protein synthesis above the preflight baseline was found for flight day 8 for all 6 subjects (P < 0.05), indicating that the astronauts showed a stress response to spaceflight.

scholarly journals Functional impact of high protein intake on healthy elderly people

2008 ◽  
Vol 295 (4) ◽  
pp. E921-E928 ◽  
Author(s):  
Stephane Walrand ◽  
Kevin R. Short ◽  
Maureen L. Bigelow ◽  
Andrew J. Sweatt ◽  
Susan M. Hutson ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Older People ◽  
Mitochondrial Function ◽  
Nitrogen Balance ◽  
Protein Intake ◽  
Muscle Protein ◽  
High Protein ◽  
Whole Body ◽  
Body Protein ◽  
Healthy Elderly

Decline in muscle mass, protein synthesis, and mitochondrial function occurs with age, and amino acids are reported to enhance both muscle protein synthesis and mitochondrial function. It is unclear whether increasing dietary protein intake corrects postabsorptive muscle changes in aging. We determined whether a 10-day diet of high [HP; 3.0 g protein·kg fat-free mass (FFM)−1·day−1] vs. usual protein intake (UP; 1.5 g protein·kg FFM−1·day−1) favorably affects mitochondrial function, protein metabolism, and nitrogen balance or adversely affects insulin sensitivity and glomerular filtration rate (GFR) in 10 healthy younger (24 ± 1 yr) and 9 older (70 ± 2 yr) participants in a randomized crossover study. Net daily nitrogen balance increased equally in young and older participants, but postabsorptive catabolic state also increased, as indicated by higher whole body protein turnover and leucine oxidation with no change in protein synthesis. Maximal muscle mitochondrial ATP production rate was lower in older people, with no change occurring in diet. GFR was lower in older people, and response to HP was significantly different between the two groups, with a significant increase occurring only in younger people, thus widening the differences in GFR between the young and older participants. In conclusion, a short-term high-protein diet increased net daily nitrogen balance but increased the postabsorptive use of protein as a fuel. HP did not enhance protein synthesis or muscle mitochondrial function in either young or older participants. Additionally, widening differences in GFR between young and older patients is a potential cause of concern in using HP diet in older people.

Diet and nitrogen metabolism during spaceflight on the shuttle

1996 ◽  
Vol 81 (1) ◽  
pp. 82-97 ◽  
Author(s):  
T. P. Stein ◽  
M. J. Leskiw ◽  
M. D. Schluter
Keyword(s):  
Protein Synthesis ◽  
Dietary Intake ◽  
Energy Intake ◽  
Nitrogen Balance ◽  
Nitrogen Retention ◽  
The Body ◽  
Whole Body ◽  
Flight Period ◽  
Flight Duration ◽  
Body Protein

Human spaceflight is associated with a loss of body protein. To investigate this problem, dietary intake, nitrogen balance, the whole body protein, and fibrinogen protein synthesis rates were measured on the crews of two Spacelab Life Sciences (SLS) shuttle missions before, during, and after spaceflight. The first mission, SLS-1, lasted 9.5 days, and the second, SLS-2, lasted 15 days. The 15N-glycine method was used for the protein synthesis measurements. The following results were obtained. 1) There was a rapid decline in weight for the first 5 days and then the body weight appeared to stabilize. 2) The mean energy intake preflight was 39.0 +/- 2.5 kcal x kg-1 x day-1 (n = 10). There was a sharp drop in dietary intake on flight day 1, with recovery by the second day, and then energy intake was constant at 30.4 +/- 1.5 kcal x kg-1 x day-1 (n = 12) for the remainder of the flight period (P < 0.05). 3) Nitrogen retention was decreased during flight, with the magnitude of the decrease lessening toward the end of the mission. The daily mean nitrogen balance changed from 58 +/- 9 mg x kg-1 x day-1 (n = 9) preflight to 16 +/- 3 mg N x kg-1 x day-1; P < 0.05; n = 11) in flight, corresponding to a loss of approximately 1 kg of lean body mass over 14 days. 4) Whole body protein synthesis was increased early in flight and on recovery, as was fibrinogen synthesis. We conclude that 1) the rapid readjustment and stabilization of energy intake and the improved nitrogen retention with increasing flight duration are consistent with a rapid metabolic accommodation to the novel environment; and that 2) the increased protein turnover indicates that a metabolic stress response is an important factor in this adjustment process.

Whole Body Protein Turnover and Resting Metabolic Rate in Homozygous Sickle Cell Disease

1989 ◽  
Vol 77 (1) ◽  
pp. 93-97 ◽  
Author(s):  
Asha Badaloo ◽  
Alan A. Jackson ◽  
Farook Jahoor
Keyword(s):  
Protein Synthesis ◽  
Energy Expenditure ◽  
Protein Turnover ◽  
Resting Metabolic Rate ◽  
Resting Energy Expenditure ◽  
Whole Body ◽  
Cell Disease ◽  
Nitrogen Flux ◽  
Body Protein ◽  
Homozygous Sickle Cell Disease

1. Whole body protein turnover and resting metabolic rate were measured in six adults with homozygous sickle cell disease (genotype HbSS) and in six normal adults (genotype HbAA) of similar age. 2. Turnover was measured with prime/intermittent oral doses of [15N]glycine over 18 h and resting energy expenditure was measured by indirect calorimetry. 3. In HbSS, nitrogen flux (0.9 ± 0.08 g day−1 kg−1), protein synthesis (6.0 ± 0.5 g day−1 kg−1) and protein degradation (5.6 ± 0.5 g day−1 kg−1) were significantly increased compared with HbAA nitrogen (flux 0.5 ± 0.02 g day−1 kg−1, protein synthesis 3.2 ± 0.2 g day−1 kg−1 and protein degradation 2.8 ± 0.2 g day−1 kg−1). 4. Resting energy expenditure was significantly higher in HbSS compared with HbAA when expressed per unit of body weight (115 ± 3 and 94 ± 4 kJ day−1 kg−1, respectively) or weight 0.75 (317 ± 6 and 269 ± 8 kJ day−1 kg−0.75, respectively). 5. The increase in protein turnover and energy expenditure suggest that patients with HbSS exist in a hypermetabolic state that requires greater dietary energy compared with HbAA.

The Effect of an Energy-Restricted Diet on the Protein Metabolism of Obese Adolescents: Nitrogen-Balance and Whole-Body Nitrogen Turnover

1980 ◽  
Vol 59 (1) ◽  
pp. 13-18 ◽  
Author(s):  
P. B. Pencharz ◽  
K. J. Motil ◽  
H. G. Parsons ◽  
B. J. Duffy
Keyword(s):  
Protein Synthesis ◽  
Nitrogen Metabolism ◽  
Nitrogen Balance ◽  
Control Period ◽  
Whole Body ◽  
Entire Group ◽  
Restricted Diet ◽  
Mean Values ◽  
Nitrogen Turnover ◽  
Protein Energy

1. The effect of an energy-restricted (46 kJ day−1 kg−1), adequate protein diet (1.47 g day−1 kg−1) on the nitrogen metabolism of five obese rapidly growing adolescents (two males and three females) was assessed by means of nitrogen-balance measurements and determination of whole-body nitrogen turnover. 2. The energy-restricted diet had no significant effect on nitrogen balance (P > 0.1) for the entire group when compared with the control dietary intake; however, significant (P < 0.01) differences in nitrogen balance were noted among individuals at each dietary interval. 3. Mean values for whole-body nitrogen turnover, protein synthesis and breakdown for the control period were: 45.5 ± 13.2 mg of nitrogen day−1 kg−1, and 5.72 ± 1.96 and 5.74 ± 1.92 g of protein day−1 kg−1 respectively. These values are 82% of those measured in infants. 4. Reducing the mean non-protein energy intake to 20 kJ day−1 kg−1 had no significant effect on whole-body nitrogen turnover, protein synthesis or protein breakdown. 5. The results are discussed in relation to the regulation of whole-body nitrogen metabolism, by dietary protein and energy intakes.

Utilization for protein synthesis of 2-ketoisocaproate relative to utilization of leucine, as estimated from exhalation of labelled CO2

1988 ◽  
Vol 75 (3) ◽  
pp. 301-307 ◽  
Author(s):  
Kenji Imura ◽  
Tetsuya Shiota ◽  
Louis M. Swain ◽  
MacKenzie Walser
Keyword(s):  
Protein Synthesis ◽  
Oral Administration ◽  
Whole Body ◽  
Body Protein ◽  
First Pass ◽  
The Mean ◽  
Co2 Excretion

1. We have previously shown that the ratio (RWBP) of incorporation of label from 2-ketoisocaproate (KIC) into the leucine of whole-body protein to the simultaneous incorporation of label from leucine itself into protein is a measure of the nutritional efficiency of KIC as a substitute for leucine. 2. In order to determine whether RWBP can be estimated indirectly from measurement of labelled CO2 excretion, rats were injected orally or intravenously with [4,5-3H]leucine and either [1-14C]leucine or [1-14C]KIC. Expired CO2 was collected for 6 h. 3. The results show that 9–14% of KIC underwent first-pass oxidation after oral administration. When isotopes were given intravenously, the mean rate of excretion of 14CO2 from KIC, after 20 min, remained 1.8 times the mean rate of excretion of 14CO2 from leucine. 4. Mean RWBP, measured in whole-body protein in rats given isotopes orally or intravenously along with small or large doses of carriers, was the same as mean RWBP estimated from mean cumulative CO2 excretion. 5. We conclude (1) that nutritional efficiency of KIC relative to leucine can be estimated from measurement of labelled CO2 excretion, and (2) that the relative inefficiency of KIC as a substitute for leucine in the rat is attributable to first-pass oxidation of 9–14% (when given orally) and 80% greater susceptibility to systemic oxidation than leucine.

Effect of rhGH and rhIGF-I treatment on protein utilization in elderly women

1997 ◽  
Vol 272 (1) ◽  
pp. E94-E99 ◽  
Author(s):  
G. E. Butterfield ◽  
J. Thompson ◽  
M. J. Rennie ◽  
R. Marcus ◽  
R. L. Hintz ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Growth Factor ◽  
Nitrogen Balance ◽  
Elderly Women ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Whole Body ◽  
High Dose ◽  
Protein Utilization ◽  
Body Protein

To assess the effect of recombinant human growth hormone (rhGH) and recombinant human insulin-like growth factor I (rhIGF-I) on protein utilization, 14 women, age 66-82 yr, were invited to participate in studies of nitrogen balance (n = 14), whole body protein turnover (n = 14), and muscle protein synthesis (n = 8). They were studied both 1 wk before and during the last week of a 1-mo regimen, to which they had been randomly assigned, of either 0.025 mg rhGH/kg once daily or rhIGF-I at 0.015 (low), 0.03 (mid), or 0.06 (high) mg/kg twice daily. Nitrogen balance increased significantly after 1 wk of treatment in all groups (P < 0.05). After 1 mo, the magnitude of this effect had diminished by 50% in the rhGH group but remained elevated throughout the treatment period with all doses of rhIGF-I. Both protein synthesis and breakdown, measured by a primed constant infusion of [15N]glycine, were significantly increased with rhGH (9% and 8%, respectively), low-dose rhIGF-I (4.5% and 4%), and high-dose rhIGF-I (18% and 17%). Net synthesis was significantly increased with rhGH (48%) and high- and mid-dose rhIGF-I (27% and 196%, respectively). Muscle protein synthesis as measured by incorporation of [1-13C]leucine increased significantly with rhGH (50%) and the mid (67%) and high (57%) doses of rhIGF-I. These data show that whole body and muscle protein synthesis are responsive to growth factor stimulation in elderly women.

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