Application of a [¹³CO₂] breath test to study short-term amino acid catabolism during the postprandial phase of a meal

Abstract

C]-labelled substrate. Such a non-steady state approach provides information that is complementary to the information obtained by steady-state methods using a primed continuous infusion of tracer amino acids during the fed state. In a model study with twenty adult male rats, two groups of animals were fed twice a day with one of two semi-synthetic iso-energetic diets. One diet contained egg white protein (EW) as the sole amino acid source. The second diet contained a mixture of free amino acids with a pattern similar to that of the EW diet. On day 5 of the dietary treatment, L-[1-13 C]leucine, either bound in EW protein or in free form, was ingested as part of the morning meal. The expired air was sampled at 30 min intervals for 5 h. The rate of recovery ranged from 0 % to 6 % of the dose/h. Up to 120 min after the onset of the meal, the recovery values for the free amino acid diet were higher than those for the EW diet. Differences in recovery reflect differences in postprandial utilisation. The differences in label recovery were mainly determined by the [ 13 C] enrichment of the expired air. As a consequence, CO 2 measurements are not mandatory when CO 2 production is comparable.

Postprandial oxidative losses of free and protein‐bound amino acids in the diet: interactions and adaptation

“…Therefore, the absolute amounts of CO 2 exhaled during the experiment were measured the day before in a similar setting. (For the exact procedure, see Bujko et al., 2007;.) For each 30‐min air sample taken from a cage, the [ 13 C]‐enrichment was determined by IRMS analysis.…”

“…The absolute amount of [ 13 C] expired was calculated using the total amount of [C] expired as CO 2 . (This is a brief description of the breath test procedure; for a detailed description of the procedure and CO 2 production measurements, see Bujko et al., 2007. )…”

“…Amino acids that cannot be stored during this period get lost for protein metabolism. Therefore, in the present study, a rat model with a [ 13 CO 2 ]‐breath test approach was used to study differences in postprandial (non‐steady‐state) catabolism of leucine ingested in free or protein‐bound form with a single meal (Bujko et al., 2007). Another method to study amino acid catabolism is to infuse the labelled substrate continuously during steady state (Metges and Barth, 2000).…”

Effect of dietary stable isotopic ratios of carbon and nitrogen on the extent of their incorporation into tissues of rats

“…The amount of carbon stable isotope 13  C varies between the C3 and C4 plants due to their use of different photosynthesis pathways while the abundance of stable nitrogen isotope 15  N in plants resembles that of their growing circumstance [2,3]. Since every feedstuff is characterized by its natural stable isotopic signature [4,5], the analysis of stable isotopes in tissues is proposed as a method to evaluate the relative contributions of nutrients from different feed sources to those deposited in tissues [6,7]. …”

Postprandial oxidative losses of dietary leucine depend on the time interval between consecutive meals: a model study with rats

“…The aim of this study was to investigate the influence of different time intervals between two consecutive equal meals on PP oxidative losses of label from egg white-bound [1- 13 (Raguso et al, 1999;Klein, 2001;Bujko et al, 2007). Body weight gain of the animals was monitored to reflect long-term protein utilization.…”