End-product Method Research Articles

Comparison of the precursor, amino acid oxidation, and end-product methods for the evaluation of protein turnover in senior dogs.

Stable isotope methods have been used to study protein metabolism in humans; however, there application in dogs has not been frequently explored. The present study compared the methods of precursor (13C-Leucine), end-products (15N-Glycine), and amino acid oxidation (13C-Phenylalanine) to determine the whole-body protein turnover rate in senior dogs. Six dogs (12.7 ± 2.6 years age, 13.6 ± 0.6 kg bodyweight) received a dry food diet for maintenance and were subjected to all the above-mentioned methods in succession. To establish 13C and 15N kinetics, according to different methodologies blood plasma, urine, and expired air were collected using a specifically designed mask. The volume of CO2 was determined using respirometry. The study included four methods viz. 13C-Leucine, 13C-Phenylalanine evaluated with expired air, 13C-Phenylalanine evaluated with urine, and 15N-Glycine, with six dogs (repetitions) per method. Data was subjected to variance analysis and means were compared using the Tukey test (P<0.05). In addition, the agreement between the methods was evaluated using Pearson correlation and Bland-Altman statistics. Protein synthesis (3.39 ± 0.33 g.kg-0,75. d-1), breakdown (3.26 ± 0.18 g.kg-0.75.d-1), and flux estimations were similar among the four methods of study (P>0.05). However, only 13C-Leucine and 13C-Phenylalanine (expired air) presented an elevated Pearson correlation and concordance. This suggested that caution should be applied while comparing the results with the other methodologies.

Measuring Protein Turnover in the Field: Implications for Military Research

Protein turnover reflects the continual synthesis and breakdown of body proteins, and can be measured at a whole-body (i.e. aggregated across all body proteins) or tissue (e.g. skeletal muscle only) level using stable isotope methods. Evaluating protein turnover in free-living environments, such as military training, can help inform protein requirements. We undertook a narrative review of published literature with the aim of reviewing the suitability of, and advancements in, stable isotope methods for measuring protein turnover in field research. The 2 primary approaches for measuring protein turnover are based on precursor- and end-product methods. The precursor method is the gold-standard for measuring acute (over several hours) skeletal muscle protein turnover, whereas the end-product method measures chronic (over several weeks) skeletal muscle protein turnover and provides the opportunity to monitor free-living activities. Both methods require invasive procedures such as the infusion of amino acid tracers and muscle biopsies to assess the uptake of the tracer into tissue. However, the end-product method can also be used to measure acute (over 9-24 h) whole-body protein turnover noninvasively by ingesting 15N-glycine, or equivalent isotope tracers, and collecting urine samples. The end-product method using 15N-glycine is a practical method for measuring whole-body protein turnover in the field over short (24 h) time frames and has been used effectively in recent military field research. Application of this method may improve our understanding of protein kinetics during conditions of high physiological stress in free-living environments such as military training.

PSIX-20 Mechanisms of Programmed Nutrition in finishing cattle

Abstract Programmed Nutrition Beef Program (Alltech Inc.) is a supplement that could reduce the use of feed additives such as Monensin and Tylosin in feedlots. The objective of this study was to examine changes in rumen fermentation when feeding Monensin/Tylosin and Programmed Nutrition. Eight steers (BW = 363 ± 22 kg) were used in a replicated 4 x 4 Latin square design experiment in a 2 x 2 factorial treatment structure where animals were fed a high-concentrate diet at 2.0 x NEm. Treatments were Control (C; conventional trace mineral supplement), Control + Monensin + Tylosin (MT), Programmed Nutrition (PN; Programmed Nutrition Beef Finisher), or Programmed Nutrition + Monensin + Tylosin (PNMT), incorporated daily to the diet at 75 g/day. Rumen pH was measured continuously for 48 h, rumen fluid was collected every 2 h for 48 h and analyzed for VFA. Dietary digestibility, nitrogen and energy balance were determined by collection of total urine and fecal output for 7 days, and indirect calorimetry for 48 h. Protein turnover was determined via 15N-glycine end-product method. The experiment was analyzed as a replicated Latin square design with mixed models of SAS (SAS Inst. Inc.). Mean differences were analyzed using LSD, rumen VFA and pH data were analyzed using repeated measures. There were no differences between treatments in DMI, ADG, dry matter digestibility and rumen pH. Addition of MT to the diet lowered fecal N output (P = 0.0092), ruminal valerate concentration (P = 0.0125) and molar proportion (P = 0.0235). When PN was fed in combination with MT it decreased ADF digestibility (P = 0.0342), protein turnover (P = 0.0211), protein synthesis (P = 0.0362) and protein degradation (P = 0.0292). Although no differences in ADG and dry matter digestibility were observed, significant metabolic changes occurred when supplementing PN with or without MT.

A Whole-Grain Diet Improves Whole-Body Protein Turnover Compared to a Macronutrient-Matched Refined-Grain Diet in Adults with Overweight/Obesity

Abstract Objectives We investigated the effect of consuming a whole-grain diet on whole-body protein metabolism compared to a macronutrient-matched refined-grain diet in adults with overweight/obesity using labelled amino acids (ClinicalTrials.gov Identifier: NCT01411540). Methods We conducted a randomized, controlled crossover trial in 14 adults with overweight/obesity (age: 40 ± 7 yrs, BMI: 33 ± 5 kg/m2) in which isocaloric, macronutrient-matched whole-grain (WG) and refined-grain (RG) diets were fully provided for two 8-week periods (with a 10-week washout period). Diets differed only in the inclusion of whole grains (50 g/1000 kcal). Body composition was measured via DEXA. Whole-body protein kinetics were assessed before and after each diet in the fasted state (13C-Leucine, primed, constant infusion) and over 24 hours (15N-Glycine, bolus). Protein kinetics were normalized to fat-free mass (FFM). Results Both diets resulted in mild weight loss (WG: −2.0 ± 2.5 kg; RG: −2.9 ± 3.3 kg; both P = 0.01 compared to baseline). Fasted-state leucine kinetics revealed greater protein synthesis (WG: 205 ± 61 µmol/kgFFM/hr; RG: 178 ± 36 µmol/kgFFM/hr; P = 0.04) and protein breakdown (WG: 235 ± 68 µmol/kgFFM/hr; RG: 203 ± 40 µmol/kgFFM/hr, P = 0.03) on a WG vs RG diet. This resulted in a more negative fasted-state net balance on a WG diet (WG: −30 ± 8 µmol/kg/hr; RG: −25 ± 6 µmol/kg/hr, P = 0.02). In contrast, 24-hour whole-body protein turnover measured by the end-product method (15N-Glycine), revealed greater protein synthesis (WG: 316 ± 135 mg protein/kgFFM/hr; RG: 250 ± 94 mg protein/kgFFM/hr) with no difference in protein breakdown, yielding a more positive 24-hr net balance on a WG diet (WG: 31 ± 21 mg protein/kgFFM/hr; RG: 10 ± 34 mg protein/kgFFM/hr). Conclusions A whole-grain diet increases whole-body leucine flux and results in a greater 24-hr net protein balance in adults with overweight/obesity compared to a refined-grain diet. This trial suggests whole-grains have an independent effect on protein metabolism and may benefit adults with overweight/obesity. Funding Sources This research was supported by the NIH (UL1 RR024989, T32DK007319 (JPK); T32AT004094 (JTM – trainee)) and an investigator-initiated grant from Nestle (JPK). Nestle Product Technology Center and Cereal Partners Worldwide provided the study meals and foods.

Measurement duration affects the calculation of whole body protein turnover kinetics but not between-day variability

BackgroundAssessment of whole body protein turnover (WBPT) can provide fundamental information about protein kinetics which underpins the conservation of lean tissue. Reliability and methodology studies on the measurement of WBPT are scarce. This study aimed to assess the effects of urine collection duration (9 versus 12 h) and the reproducibility of WBPT with the end product method calculated from ammonia as the end product. MethodsWBPT was assessed in 21 healthy participants (11M, 10F) on 2 test days. WBPT was assessed using the end product method with a single dose of 15N glycine with ammonia as end product in a postprandial state with 9 and 12-h urine collections. ResultsThe CV for protein flux averaged 10% and 12% for 9 and 12-h urine collections respectively. Protein flux, synthesis and balance were significantly higher and protein breakdown significantly lower with 9-h urine collections compared to 12-h collections (P < 0.01) and there was a trend towards increasingly greater overestimation of 9-h calculated WBPT kinetics with greater overall rates of WBPT. Correlations between the 9 and 12-h values were strong (r > 0.962, P < 0.001 for all variables). ConclusionsThe reproducibility of WBPT with ammonia as the end product was similar to previously reported reproducibility of the gold standard precursor technique. The use of a 12-h urine collection is more effective to achieve full turnover of the ammonia free amino acid (AA) pool.

The 13C bicarbonate method: an inverse end product method for measuring CO2 production and energy expenditure

We reconsider the principle of the 13C bicarbonate (NaH13CO3) method (13C-BM) for the determination of the CO2 production to obtain an estimate of energy expenditure (EE). Its mathematical concept based on a three-compartmental model is related to the [15N]glycine end product method. The CO2 production calculated by the 13C-BM, RaCO2(13C) is compared to the result from the indirect calorimetry, RCO2(IC). In an interspecies comparison (dog, goat, horse, cattle, children, adult human; body mass ranging from 15 to 350 kg, resting and fasting conditions) we found an excellent correlation between the results of 13C-BM and IC with RCO2(IC) = 0.703 × RaCO2(13C), (R2 = 0.99). The slope of this correlation corresponds to the fractional 13C recovery (RF(13C)) of 13C in breath CO2 after administration of NaH13CO3. Significant increase in RF(13C) was found in physically active dogs (0.95 ± 0.14; n = 5) vs. resting dogs (0.71 ± 0.10, n = 17; p = .015). The 13C recovery in young bulls was greater in blood CO2 (0.81 ± 0.05) vs. breath CO2 (0.73 ± 0.05, n = 12, p < .001) and in ponies with oral (0.76 ± 0.03, n = 8) vs. intravenous administration of NaH13CO3 (0.69 ± 0.07; n = 8; p = .026). We suggest considering the 13C-BM as a ‘stand-alone’ method to provide information on the total CO2 production as an index of EE.

Whole-body protein turnover reveals the cost of detoxification of secondary metabolites in a vertebrate browser

The detoxification limitation hypothesis predicts that the metabolism and biotransformation of plant secondary metabolites (PSMs) elicit a cost to herbivores. There have been many attempts to estimate these costs to mammalian herbivores in terms of energy, but this ignores what may be a more important cost-increases in protein turnover and concomitant losses of amino acids. We measured the effect of varying dietary protein concentrations on the ingestion of two PSMs (1,8 cineole-a monoterpene, and benzoic acid-an aromatic carboxylic acid) by common brushtail possums (Trichosurus vulpecula). The dietary protein concentration had a small effect on how much cineole possums ingested. In contrast, protein had a large effect on how much benzoate they ingested, especially at high dietary concentrations of benzoate. This prompted us to measure the effects of dietary protein and benzoate on whole-body protein turnover using the end-product method following an oral dose of [(15)N] glycine. Increasing the concentration of dietary protein in diets without PSMs improved N balance but did not influence whole-body protein turnover. In contrast, feeding benzoate in a low-protein diet pushed animals into negative N balance. The concomitant increases in the rates of whole-body protein turnover in possums eating diets with more benzoate were indicative of a protein cost of detoxification. This was about 30% of the dietary N intake and highlights the significant effects that PSMs can have on nutrient metabolism and retention.

Whole-body protein turnover in peritoneal dialysis patients: a comparison of the [15N]glycine end product and the [13C]leucine precursor methods

Two well-described methods for measuring whole-body protein turnover (WBPT) are the precursor method using a primed continuous infusion of [1-(13)C]leucine and the end-product method with a single oral dose of [(15)N]glycine. We previously measured the effects of amino acid (AA)-containing dialysate on protein anabolism in patients undergoing continuous ambulatory peritoneal dialysis (CAPD) using the [1-(13)C]leucine technique. Here, we examine whether the less invasive [(15)N]glycine method could also be appropriate for studying nutritional interventions. We compared the results of WBPT measurements using a single oral dose of [(15)N]glycine with those obtained with the primed continuous infusion of [1-(13)C]leucine during AA and glucose (G) dialysis and G-only dialysis in 12 CAPD patients in the fed state. The end-product method showed a wide variation for protein synthesis and breakdown measurements. It did not detect a small but significant increase in protein synthesis with AA-containing dialysate as shown by the precursor method. However, a significant relation was found between both methods for net protein synthesis (i.e. protein synthesis minus breakdown) during AA and G (r = 0.75, P = 0.005) or during G-only dialysis (r = 0.86, P < 0.001). The agreement between the two methods for the net protein balance was good [intra-class correlation coefficient (ICC) = 0.88] with G-only dialysate and moderate (ICC = 0.70) with AA and G dialysate. While the precursor method shows less variation, the more convenient end-product method may be useful in larger groups of selected patients including those on PD.

Bacterial protein meal in diets for pigs and minks: Comparative studies on protein turnover rate and urinary excretion of purine base derivatives

The effect of increasing the dietary content of bacterial protein meal (BPM) on protein turnover rate, and on nucleic acid and creatinine metabolism in growing minks and pigs was investigated in two experiments. In each experiment, 16 animals were allocated to four experimental diets. The diets containing no BPM served as controls, i.e. for minks diet M1, for pigs P1; the experimental diets contained increasing levels of BPM to replace fish meal (minks) or soybean meal (pigs), so that up to 17% (P2), 20% (M2), 35% (P3), 40% (M3), 52% (P4), and 60% (M4) of digestible N was BPM derived. Protein turnover rate was measured by means of the end-product method using [15N]glycine as tracer and urinary nitrogen as end-product. In minks, protein flux, synthesis, and breakdown increased significantly with increasing dietary BPM. In pigs, diet had no observed effect on protein turnover rate. The intake of nucleic acid nitrogen (NAN) increased from 0.15 g/kg W0.75 on M1 to 0.26 g/kg W0.75 on M3 and M4 in the mink experiment, and from 0.08 g/kg W0.75 on P1 to 0.33 g/kg W0.75 on P4 in the pig experiment. Increased NAN intake led, in both experiments, to increased allantoin excretion. Analysis of species effects showed that minks excreted 1.72 mmol/kg W0.75 of allantoin, significantly more than the 0.95 mmol/kg W0.75 excreted by pigs. In minks, approximately 96% of the excreted purine base derivatives consisted of allantoin, whereas in pigs approximately 93% did. Thus, increasing the dietary content of BPM increased protein turnover rate in minks but not in pigs, and allantoin excretion increased with increasing dietary BPM although it seemed that mink decomposed purine bases to their end-product more completely than pigs did. Collectively these data show that BPM is a suitable protein source for pigs and mink, and recorded differences between species were to a large extent due to differences in protein retention capacity and muscle mass.

Influence of dietary lysine level on whole-body protein turnover, plasma IGF-I, GH and insulin concentration in growing pigs

Abstract Four growing pigs (initial liveweight 25.9 ± 0.54 kg, final liveweight 43.0 ± 1.06 kg) were used to study the effect of dietary lysine level on nutrient digestibility, whole-body protein turnover, plasma insulin-like growth factor-I (IGF-I), growth hormone (GH), insulin, glucose, and urea nitrogen (PUN). Four diets, containing 7.0 g (L1), 9.5 g (L2), 12.0 g (L3) and 14.5 g (L4) lysine per kg diet respectively, were formulated as experimental treatments. The animals and diets were allocated in a 4 × 4 Latin square design. Nitrogen (N) metabolism and whole-body protein turnover were measured by classical method and single-dose 15 N end-product method, respectively. The blood samples were taken at the end of each experimental period. Results showed that N retention (NR) and N biological value (NBV) were significantly increased from L1 to L4 ( P P > 0.05). There was no significant difference on dry matter (DM) digestibility, organic matter (OM) digestibility and N digestibility between different treatments ( P > 0.05). Whole-body protein synthesis, protein degradation and protein accretion increased markedly from L1 to L2 ( P y , g/kg W 0.75 /d) increased with dietary lysine ( x , g/kg) in a quadratic manner: y = − 0.09 x 2 + 2.12 x − 5.14 ( r 2 = 0.96, n = 4, P The results also showed that differences in plasma IGF-I, GH, glucose and PUN concentration between different treatments were not significant ( P > 0.05). Plasma insulin concentration ( y , μIU/ml) was increased with dietary lysine ( x , g/kg) in a quadratic manner: y = 0.23 x 2 − 4.10 x + 32.25 ( r 2 = 0.99, n = 4, P y , g/d) and plasma IGF-I ( x , ng/ml): y = − 3.1 × 10 − 3 x 2 + 1.31 x − 122.28 ( r 2 = 0.99, n = 4, P It was concluded that dietary lysine level had a significant influence on NR and whole-body protein turnover but not on plasma IGF-I and GH concentration. Plasma IGF-I may be an important factor controlling N metabolism of growing pigs. Further research was needed to study the mechanism.

The end-product method of measuring whole-body protein turnover: a review of published results and a comparison with those obtained by leucine infusion

The present review summarizes the results of all published papers on whole-body protein turnover in man measured by [15N]glycine and the end-product method using both urea and ammonia. It begins with a short account of the underlying assumptions and the justification for the use of [15N]glycine. The results are then compared with those of a large sample of measurements by the 'gold standard' precursor method with continuous infusion of [13C]leucine. The pros and cons of the two methods are compared and it is suggested that there is a place for further work by the less invasive end-product method, particularly for population studies of the genetic, environmental and functional determinants of whole-body rates of protein synthesis.

Relationship of maternal protein turnover and lean body mass during pregnancy and birth length

Epidemiological evidence shows that small size at birth is associated with an increased risk of developing cardiovascular and metabolic disease in adult life. We have examined the relationships between size at birth and maternal body composition and protein turnover in normal pregnant women. A group of 27 multiparous Caucasian women with singleton pregnancies were studied at around 18 and 28 weeks' gestation. Body composition was determined by anthropometry, and whole-body protein turnover was estimated by using a single oral dose of [(15)N]glycine and the end-product method. The baby's weight and length were measured within 48 h of birth. Mothers with a greater lean body mass had higher rates of protein turnover at 18 weeks' gestation. This association was largely accounted for by differences in the mother's visceral, rather than muscle, mass. Mothers who had higher protein turnover at 18 weeks' gestation had babies that were longer at birth. After adjustment for the duration of gestation and the baby's sex, 26% of the variation in length at birth was accounted for by maternal protein synthesis at 18 weeks' gestation. Maternal protein intake was not associated with the baby's birth length. Thus the mother's ability to nourish her fetus is influenced by her body composition and her rate of protein turnover. Dietary intake does not adequately characterize this ability.

Effect of latex modification of Portland cement matrices on properties of heavy metal immobilized products

Solidification and stabilization are considered to be a successful method for the treatment of hazardous metal sludges because the properties of the end product and cheap methods of disposal. Although solidification often limits the undue leaching of metals, the highly porous nature of the cement matrices are susceptible to attack by various solutes after placement in landfills, thus reducing their strength and durability. Improved methods of treatment for the metal sludges are required. Modification of the physical properties, especially porosity, of the cement matrices can improve the properties of the final product. The objective of this research was to study the effect of polymer modification of the cement matrices on the strength and leachability of the solidified and stabilized product. The results of this preliminary study showed a 10-fold reduction in the leachability of the metals, although no noticable difference in strength values was noted.

Protein pulse feeding improves protein retention in elderly women

Adequate protein nutrition could be used to limit gradual body protein loss and improve protein anabolism in the elderly. We tested the hypothesis that an uneven protein feeding pattern was more efficient in improving protein anabolism than was an even pattern. After a controlled period, 15 elderly women (mean age: 68 y) were fed for 14 d either a pulse diet (n = 7), providing 80% of the daily protein intake at 1200, or a spread diet (n = 8), in which the same daily protein intake was spread over 4 meals. Both diets provided 1.7 g protein x kg fat-free mass (FFM)(-1) x d(-1). Protein accretion and daily protein turnover were determined by using the nitrogen balance method and the end product method (ammonia and urea) after an oral dose of [15N]glycine. Nitrogen balance was more positive with the pulse than with the spread diet (54 +/- 7 compared with 27 +/- 6 mg N x kg FFM(-1) x d(-1); P < 0.05). Protein turnover rates were also higher with the pulse than with the spread diet (5.58 +/- 0.22 compared with 4.98 +/- 0.17 g protein x kg FFM(-1) x d(-1); P < 0.05), mainly because of higher protein synthesis in the pulse group (4.48 +/- 0.19 g protein x kg FFM(-1) x d(-1)) than in the spread group (3.75 +/- 0.19 g protein x kg FFM(-1) x d(-1)) (P < 0.05). A protein pulse-feeding pattern was more efficient than was a protein spread-feeding pattern in improving, after 14 d, whole-body protein retention in elderly women.

Whole Body Protein Metabolism Estimated by 15N Tracer Experiments and Body Composition of Mice Selected for Different Growth Parameters

Whole body protein synthesis was investigated in growing male mice which were long-time selected for high carcass protein amount (DU-6P, protein line) or for high body weight (DU-6, growth line) and in the unselected randomly bred control (DU-Ks). Six mice/line were housed singly in metabolic cages for the estimation of N balance, whole body protein synthesis (end-product method, single dose of 15N-labelled amino-acid mixture), and N distribution in the body. Another six mice/line were used for the determination of the body composition. All mice had free access to a commercial stock diet (crude protein 268 g, gross energy 19 MJ/kg dry matter) and to water. Body weight of both selection lines was about twice that of control mice at the same age. Selection for high body weight resulted in higher body fat content. Scaled to the corresponding body protein pools, the protein synthesis rates of selected mice were significantly higher than in controls, but were not significantly different between both selection lines in contrast to the protein deposition rates. The higher protein accretion in the protein line in comparison to the growth line seems to be due to a combination of a lower protein breakdown and an increased protein synthesis rate.

Whole-body protein turnover in humans fed a soy protein-rich vegetable diet

This study was designed to compare the whole-body protein turnover in humans after the ingestion of a soy protein-rich vegetable diet with that of a control group fed a western animal protein-rich diet. Twelve male volunteers were divided into two groups of six subjects who were given for two weeks either a 85% vegetable protein diet (diet VP) or a control western animal protein-rich diet (diet AP). Whole-body protein turnover was estimated at the end of the two-week controlled diet period using the [15N]-glycine end-product method. Nitrogen flux rates were determined in the fed state (1.3 g protein/kg) over a 9 h period after the dose of [15N]-glycine was given. After the 9 h of the test, the urinary ammonia excretion was significantly higher in the group receiving the diet AP than that in the group receiving the diet VP (P < 0.05). In contrast, there was no significant difference for both total nitrogen and urea nitrogen excretions. Both the protein synthesis and the protein breakdown were similar in both groups. In the same way, the net protein deposition measured in the fed state during 9 h was similar for both diets at 0.07 g/kg/h. Young adults fed 1.3 g/kg/d of either meat or vegetable protein-rich diet for two weeks did not show a different protein turnover.

Measurement of protein turnover in normal man using the end-product method with oral [15N]glycine: comparison of single-dose and intermittent-dose regimens

The 'single-dose end-product' approach for the measurement of protein turnover is the only method suited for application to free-living individuals and for field studies. However, the method has never been widely accepted because the results obtained appear to vary from one situation to another. There is the need for a formal comparison of the different approaches that have been used and the assumptions on which they are based in order to be able to understand the extent to which the variation in the results obtained is real or might be attributed to methodological differences. The present study used the 'prime/intermittent-dose end-product' approach over 18 h as a reference with which to compare the 'single-dose end-product' approach, with urine being collected for periods of 9 to 48 h. N flux was derived in a total of thirteen normal men using oral [15N]glycine and measurement of 15N enrichment in urinary NH3 or urea, with isotope being given either as prime/intermittent doses or a single dose in separate studies. The pattern of results was similar to those reported in the literature. In all studies the rates of N flux derived from urea were higher than those derived from NH3, under equivalent conditions, by about 25-30%. The single-dose approach, with urine collection over 9 h, gave results which were consistently higher than the prime/intermittent-dose approach. The extent of the difference was influenced by the duration of time over which the cumulative excretion of isotope in urine was determined, and with NH3 as the end-product the most consistent estimates of N flux could be obtained with a urine collection of at least 12 h and no greater than 24 h. With urea as the end-product, correction for the label retained in the body pool at 9 h gave similar results for N flux to those derived from the total excretion of label in urea over 24 h. The derivation of values for protein synthesis and protein degradation from measures of flux requires care to ensure that the time periods over which N intake and excretion are measured accord with those for which the measurement of flux apply. It is concluded that measurements of protein turnover similar to those obtained with the prime/intermittent-dose approach can be obtained with the single-dose approach in the fed state during the daytime, either from the excretion of label in urinary NH3 over a period of 12 h or with the excretion of label in urinary urea over a period of 24 h. The suitability of the method for use in the fasted state or at night time remains to be determined.

Whole-body protein turnover in response to hyperinsulinemia in humans postabsorptively with [15N]glycine as tracer

Studies using stable isotopes to determine the effect of insulin on whole-body protein turnover have given conflicting results. The precursor approach to studying healthy subjects in a postabsorptive state shows reductions in breakdown and oxidation; with end product methods in parenterally fed patients no such changes are seen. To explain these discrepancies, we measured protein turnover with and without euglycemic hyperinsulinemic clamping postabsorptively in nine healthy subjects by using single-dose [15N]glycine with calculations based on ammonia and urea end product excretion. With and without clamping, respectively, insulin reduced nitrogen (22.1 and 48.2 mg.kg-1.9 h-1, P < 0.01) and urea (15.8 and 37.5 mg.kg-1.9 h-1, P < 0.05) but increased ammonia (7.7 and 5.0 mg.kg-1.9 h-1, P < 0.05) excretion. Although the urea end product method suggested that insulin tended to reduce both protein breakdown and synthesis, the protein metabolism changes detected with the ammonia end product method tended to be in the opposite direction. The [15N]glycine ammonia end-product method may be inappropriate for studies during insulin infusion because of insulin's effect on ammonia excretion.

Influence of Food Restriction and Compensatory Growth on Protein Synthesis and Breakdown in Growing Rats

Abstract The experiment was carried out with 24 male albino rats (5 weeks old, live weight 79 ± 5.1 g) divided into 2 groups. Gr. 1 (control group) was fed the commercial breeding food Ssniff with 22.4% crude protein ad lib., Gr. 2 (test group) for the first fortnight a mixture of the breeding food/cellulose 60/40 (restriction period) and subsequently for the second fortnight (compensatory period) also the breeding food ad lib. During both of these periods an 8 day N balance trial and a 4 day 15N tracer trial were included for estimation of growth rate and protein synthesis rate. Protein synthesis was ascertained by the endproduct method (oral application, single dose, mixture of 12 15N-labelled amino acids); protein breakdown was calculated as the difference of protein synthesis rate and growth rate. The estimated rates were converted into fractional ones by referring to the body N content of corresponding animals. From the results of this experiment is concluded: The smaller N balance during moderate nutritional restriction can be attributed to a decrease of protein synthesis. The compensatory growth of the animals during the realimentation period is caused by an increase of protein synthesis and the enhanced protein conversion. Protein degradation is nearly unaffected.

Bestimmung von kinetischen Parametern des Proteinmetabolismus bei wachsenden Ratten in Verbindung mit Energieumsatzmessungen. 1. Mitteilung. Bestimmung von kinetischen Parametern des Proteinmetabolismus in Abhängigkeit von der Lebendmasse und dem Proteingehalt des Futters

The digestibility, the N balance, the rate of protein synthesis and other parameters, characterising the protein metabolism in dependence on live weight, protein- and energy supply are estimated on Wistar rats (4-5 animals/group). These experiments were done in 5 alternating consecutive growth and energy maintenance periods at 4 different levels of protein (6, 10, 17, 26% CP) during the live weight period of 70 to 230 g. The rate of protein synthesis was calculated from the course of renale 15N excretion by means of the end product method after giving a single dose of a mixture of 17 15N labelled amino acids. N deposition, rate of protein synthesis and flux rate increased with the protein level of the ration. During maintenance these data were much lower, but showed the same dependence on the protein level. The absolute protein synthesis (g/d) increased up to the live weight of 130... 180 g and decreased afterwards according to the age. The reutilization rate varied between 44 and 87% and decreased with increasing dietary protein level by 27% and during proceeding age by 8 ... 12%. In contrast to the absolute metabolism rates (g/d) the fractional rates (%/d) clearly decreased with the age of the animals. The stimulation of these rates by the dietary protein level resembled that for the absolute rates of synthesis. The protein deposition showed the typical course of a growing curve according to the N intake and the protein synthesis showed practically the same course but on a higher level. The break down remained constantly (approximately 140 mg N/d) up to an N intake of about 360 mg and afterwards it increased too.