Growth versus metabolic tissue replacement in mouse tissues determined by stable carbon and nitrogen isotope analysis

Abstract

Stable-isotope signatures in animal tissues presumably reflect the local food web. However, that assumption may be complicated by differential nutrient routing, fractionation, and the possibility that large organisms are not in isotopic equilibrium with seasonally available food sources. Additionally, the rate at which organisms incorporate the isotopic signature of a food is largely unknown. In this study we assessed the rate of carbon- and nitrogen-isotope turnover in liver, muscle, and blood in mice (Mus musculus L., 1758) following a diet change. We report the proportion of tissue turnover caused by growth versus that caused by metabolic tissue replacement. Growth accounted for approximately 10% of observed tissue turnover in adult mice. Blood carbon had the shortest half-life (16.9 days), followed by muscle carbon (23.9 days). Liver carbon turnover, which was slower than blood and muscle carbon turnovers, was not as well described by the exponential decay equations. All tissues primarily reflect the protein carbon signature rather than the carbohydrate carbon signature. The nitrogen signature in all tissues was enriched by 3‰–5‰ over their diets' nitrogen signature, depending on tissue type, and the isotopic turnover rates of nitrogen in blood and muscle were comparable with those observed for carbon.

Turnover and fractionation of nitrogen stable isotope in tissues of grass carp Ctenopharyngodon idellus

“…The relative importance of metabolism versus growth in nitrogen isotopic turnover is determined by bioenergetic allocations. The faster the metabolism, the quicker turnover rate, and therefore the shorter the half-life of the tissue (MacAvoy et al 2005). Such correlation was well confirmed by the results of the present experiment.…”

“…Previous studies have been mainly focused on endotherms, such as mammals and birds (Hobson et al. 2000, MacAvoy et al 2005, whereas ectotherms, especially fish tissues, have rarely been addressed so far (Hesslein et al 1993, Harvey et al 2002, MacNeil et al 2005, Suring & Wing 2009, Sulak et al 2012.…”

“…Previous studies have been mainly focused on endotherms, such as mammals and birds (Hobson et al. 2000, MacAvoy et al 2005, whereas ectotherms, especially fish tissues, have rarely been addressed so far (Hesslein et al 1993, Harvey et al 2002, MacNeil et al 2005, Suring & Wing 2009, Sulak et al 2012.In the present study, the nitrogen stable isotope turnover was analyzed for 3 types of grass carp tissue by means of a diet-switch study. The results showed that the nitrogen isotopic signatures of grass carp tissue reflected and approached those of the new diet (experimental feed), and the nitrogen isotopic turnover processes were mathematically predictable following the turnover models, as reported by others (Guelinckx et al 2007).…”

Effect of different diets on proteolytic enzyme activity, trypsinogen gene expression and dietary carbon assimilation in Senegalese sole (Solea senegalensis) larvae

“…Iterative non-linear regression was used to estimate the proportion of isotopic change in tissue caused by metabolic turnover (m). The time necessary for half of the body tissue to reach isotopic equilibrium or to be replaced after consuming the new diet (half time, t 50 ) was also estimated from the parameters in the exponential model (MacAvoy et al, 2005). The C:N ratio of fish at different larval stages was estimated in order to associate C:N and isotopic changes with nutritional variations occurring as endogenous and exogenous nutrients were utilized.…”

“…Changes in the isotopic composition of organisms generally results from dietary shifts (Hesslein et al, 1993;Carleton and Martínez del Rio, 2010) and the rate of isotopic incorporation depends on tissue growth and metabolic turnover (Fisk et al, 2009). Carbon is present in all organic molecules hence carbon turnover can be considered as an indicator of total tissue turnover (MacAvoy et al, 2005).…”