Whole-Body Protein Parameters in Premature Infants: A Comparison of Different 15N Tracer Substances and Different Methods

Abstract

[15N]glycine, [15N]leucine, and [15N]yeast protein thermitase hydrolysate (YPTH) as tracers for investigating the protein turnover rates in premature infants were studied in nine human milk-fed neonates (born after 32 to 34 wk of gestation) by paired comparison of the tracers. The 15N enrichment of total urinary nitrogen and ammonia after administration of a single oral dose of 15N was measured by emission spectrometry. Flux rates were calculated using a three-compartment model and the ammonia end product method. The mean whole-body protein synthesis rates, as determined by the three-compartment model derived from the three 15N tracers, differed significantly (p less than 0.01) among [15N]glycine (15.9 g/kg/d), [15N] leucine (9.1 g/kg/d), and 15N-YPTH (5.9 g/kg/d). When the corresponding rates were determined from the excretion of label in ammonia, the results showed the opposite tendency; the lowest apparent synthesis rates were found after [15N]glycine (7.5 g/kg/d), followed by [15N]leucine (14.4 g/kg/d), and the highest figure resulted after [15N] YPTH (16.7 g/kg/d). The results of this comparison substantiate the assumption that there are methodologic errors in connection with the use of different tracers and models for the calculation of whole-body protein parameters in preterm infants, with respect to the main requirement for tracer kinetic studies; the tracer nitrogen must be representative of total amino acid nitrogen. Seen in this light, mixtures of completely labeled amino acids such as YPTH may represent the most reliable tracer substance.(ABSTRACT TRUNCATED AT 250 WORDS)

15N-excretion of heat-killed Lactobacillus casei in humans

“…Ammonia was separated in vessels by micro diffusion, following alkalisation of the urine with NaOH and trapped in boric acid. (Faust et al, 1981;Wutzke et al, 1992). A blood sample was taken 2 h after 15 N-L.casei administration at 1000 hours.…”

Effect of alcohol consumption on whole-body protein turnover in healthy adults

“…The protein flux rates Q, S, B, and N were calculated by using a three-compartment model ( Figure 1) as already described earlier in detail [9,10,12,[17][18][19]. Briefly, our numerical treatment of the experimental data was adjusted on a 48 h plateau value of the total urinary cumulative 15 Nexcretion.…”

“…Thereafter, the 15 N-YP was extracted in a slightly alkaline solution and separated from the nucleic acids by hot trichloracetic acid precipitation at pH 1.5 and 80 • C. The yeast fat was removed by washing with ethanol (96 vol%, Merck), and the remaining white wet 15 N-YP was finally air-dried at 50 • C. The 15 N-enrichment, the total nitrogen-, and the 15 N-content amounted to 88.76 at%, 13.3, and 11.84 mg/100 mg dry 15 N-YP, respectively. The complete procedure, including the composition of the yeast medium, has been described previously in detail [10][11][12][13][14].…”

“…However, little is known about possible changes in the whole-body protein turnover rate (Q) and other parameters of the protein metabolism in response to the consumption of alcohol in moderate dosages, which is also of great scientific interest. Our Research Laboratory has long-time experience in 15 N-labelling and in using yeast protein for tracer kinetic studies in humans [9][10][11][12]. The particular advantage of applying a universally 15 N-labelled yeast protein ( 15 N-YP) for evaluating the protein flux rates is the fact that the 15 N-dose is spread among all proteinogenic amino acids.…”

“…The particular advantage of applying a universally 15 N-labelled yeast protein ( 15 N-YP) for evaluating the protein flux rates is the fact that the 15 N-dose is spread among all proteinogenic amino acids. In contrast to the application of a single 15 N-labelled amino acid as a tracer substance, a 15 N-YP gives a more representative picture of the protein metabolism, particularly when specific metabolic conditions are to be examined [9][10][11][12]. Therefore, in the present study, 15 N-YP was used for measuring the percentage of urinary and faecal 15 N-excretion and for calculating the protein flux rates either before or after moderate red wine consumption.…”