Tracking the oxidative kinetics of carbohydrates, amino acids and fatty acids in the house sparrow using exhaled 13CO2

Abstract

SUMMARYClinicians commonly measure the 13 CO 2 in exhaled breath samples following administration of a metabolic tracer (breath testing) to diagnose certain infections and metabolic disorders. We believe that breath testing can become a powerful tool to investigate novel questions about the influence of ecological and physiological factors on the oxidative fates of exogenous nutrients. Here we examined several predictions regarding the oxidative kinetics of specific carbohydrates, amino acids and fatty acids in a dietary generalist, the house sparrow (Passer domesticus). After administering postprandial birds with 20mg of one of seven 13 Clabeled tracers, we measured rates of 13 CO 2 production every 15min over 2h. We found that sparrows oxidized exogenous amino acids far more rapidly than carbohydrates or fatty acids, and that different tracers belonging to the same class of physiological fuels had unique oxidative kinetics. Glycine had a mean maximum rate of oxidation (2021nmolmin ), and differed significantly in the extent to which each was oxidized, with 0.73%, 0.63% and 0.21% of palmitic, oleic and stearic acid tracers oxidized, respectively.

Obese super athletes: fat-fueled migration in birds and bats

“…Additional field measurements of wild birds captured in mid-flight are needed to replicate earlier studies. Although isotopic tracing of lipoproteins and NEFA to measure flux during endurance flights will not be trivial (Magnoni et al, 2008;McCue et al, 2010;Vaillancourt and Weber, 2007), this could be performed to conclusively test the lipoprotein hypothesis.…”

The insectivorous batPipistrellus nathusiiuses a mixed-fuel strategy to power autumn migration

“…Second, we measured d 13 C V-PDB in breath collected from P. nathusii after having fed on a dose of 13 C-labelled amino acids (glycine) or 13 C-labelled fatty acids (palmitic acid). We calculated the cumulative oxidation of both substrates [32], and predicted that migratory P. nathusii oxidize the exogenous amino acid but not the fatty acid. Our experiments may shed new light on the physiological abilities and constraints of insectivorous bats when performing long-distance migration.…”

“…Any deviation between assumed and true bicarbonate retention factors may not affect the relative difference in our estimates of compound-specific oxidation rates because this constant applies to both calculations in the same way. Further, we have refrained from controlling for the loss of 13 C in urea, because the suggested stoichiometric correction [32] [32]). In the present experiment, we have used glycine (2 C and 1 N), yielding a k-factor of 0 ml for the volume of CO 2 produced for each milligram of oxidized glycine.…”

The speed and metabolic cost of digesting a blood meal depends on temperature in a major disease vector

“…where m is the molar mass of each tracer and K is the volume of CO 2 produced per gram of mixed substrate oxidized using a value of 1.0 l g −1 (Gay et al, 1994;McCue et al, 2010;Welch et al, 2016). Cumulative tracer oxidation was estimated by integrating T across time, and the percent dose oxidized was estimated using the average blood meal size that we previously determined under identical rearing and feeding conditions.…”

“…carbohydrates, lipids and amino acids) provided this energy. Indeed, the postprandial oxidative kinetics of different classes of nutrients have been studied in other animals including humans (Hoekstra et al, 1996;Labayen et al, 2004a,b), rodents , reptiles (McCue et al, 2015a) and birds (Swennen et al, 2007;McCue et al, 2010McCue et al, , 2011. These studies show that both dietary carbohydrates and proteins are readily used for immediate energy during digestion.…”