HR: 0830h
AN: B31E-0366    [PDF]
TI: Growth versus metabolic tissue replacement in mouse tissues determined by stable carbon and nitrogen isotope analysis
AU: * MacAvoy, S E
EM: macavoy@american.edu
AF: Biology Department American University, 4400 Mass. Ave. NW, Washington, DC 20016 United States
AU: Jamil, T
EM: Jamil@american.edu
AF: Biology Department American University, 4400 Mass. Ave. NW, Washington, DC 20016 United States
AU: Macko, S A
EM: sam8f@virginia.edu
AF: Department of Environmental Sciences University of Virginia, Clark Hall, Charlottesville, VA 22903 United States
AU: Arneson, L S
EM: larneso@american.edu
AF: Biology Department American University, 4400 Mass. Ave. NW, Washington, DC 20016 United States
AB: Stable isotope analysis is becoming an extensively used tool in animal ecology. The isotopes most commonly used for analysis in terrestrial systems are those of carbon and nitrogen, due to differential carbon fractionation in C3 and C4 plants, and the approximately 3$\permil$ enrichment in 15N per trophic level. Although isotope signatures in animal tissues presumably reflect the local food web, analysis is often complicated by differential nutrient routing and fractionation by tissues, and by the possibility that large organisms are not in isotopic equilibrium with the foods available in their immediate environment. Additionally, the rate at which organisms incorporate the isotope signature of a food through both growth and metabolic tissue replacement is largely unknown. In this study we have assessed the rate of carbon and nitrogen isotopic turnover in liver, muscle and blood in mice following a diet change. By determining growth rates, we were able to determine the proportion of tissue turnover caused by growth versus that caused by metabolic tissue replacement. Growth was found to account for approximately 10% of observed tissue turnover in sexually mature mice (Mus musculus). Blood carbon was found to have the shortest half-life (16.9 days), followed by muscle (24.7 days). Liver carbon turnover was not as well described by the exponential decay equations as other tissues. However, substantial liver carbon turnover was observed by the 28th day after diet switch. Surprisingly, these tissues primarily reflect the carbon signature of the protein, rather than carbohydrate, source in their diet. The nitrogen signature in all tissues was enriched by 3 - 5$\permil$ over their dietary protein source, depending on tissue type, and the isotopic turnover rates were comparable to those observed in carbon.
DE: 1040 Isotopic composition/chemistry
DE: 1099 General or miscellaneous
SC: Biogeosciences [B]
MN: 2003 Fall Meeting