Modelling and determination of metabolic pools by stable carbon isotopes in the avian duodenal mucosa and albumen

Stable isotope analyses have helped in assessing dietary switches if the diet undergoes metabolic alteration (isotopic exchange). However, when considering the effects over time of switching from one diet to another, one can assess how quickly the new diet is incorporated into tissues via the isotopic renewal or incorporation rate, or turnover. Turnover is obtained using exponential curves that fit the original data, allowing the determination of practical order parameters such as the half-life (T) and the turnover constant (k). Researchers have found that metabolic incorporation can be fractionated. The resulting fractions, called metabolic pools, are identified using the linearization of the isotopic exchange model and its linear fit. This fractionation methodology is still not well defined. The objective of this study was to assess the behaviour of the metabolic renewal rate (turnover) in fractionated form, explain the theory, and apply it to data from the avian duodenal mucosa and albumen. We concluded that the duodenal mucosa has one metabolic pool, with a half-life of 1.23 days, and that the albumen has two metabolic pools, with half-lives of 1.89 and 6.32 days.