Meeting Abstract

44.5  Tuesday, Jan. 5  Tracking the oxidative kinetics of carbohydrates, amino acids, and fatty acids in the house sparrow using exhaled 13CO2 MCCUE, Marshall/D*; SIVAN, Orit; MCWILLIAMS, Scott/R; PINSHOW, Berry; Blaustein Institutes for Desert Research; Ben Gurion University; Univ Rhode Island; Blaustein Institutes for Desert Research mmccue@bgu.ac.il

Clinicians have measured the ¹³CO₂ in exhaled breath samples following administration of a metabolic tracer (breath testing) for decades, but comparative physiologists have only recently begun using breath testing to study the oxidation of exogenous sugars in nectivores. We examined several predictions regarding the oxidative kinetics of various 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 ¹³C-labled tracers, we measured rates of ¹³CO₂ production every 15 min. over 2 hours. 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^-1) that was significantly higher than that of leucine (351 nmol min^-1), supporting our prediction that nonessential amino acids are oxidized more rapidly than essential amino acids. Exogenous glucose and fructose were oxidized to a similar extent (5.9% of dose), but the time required to reach maximum rates of oxidation was longer for fructose. The maximum rates of oxidation were significantly higher when exogenous glucose was administered as an aqueous solution (122 nmol min^-1), rather than as an oil suspension (93 nmol min^-1), supporting our prediction that exogenous lipids negatively influence rates of exogenous glucose oxidation. Dietary fatty acids were oxidized at the lowest rates (2 – 6 nmol min^-1), and differed significantly in the quantity of which each was used, with 0.73%, 0.63%, and 0.21% of palmitic, oleic, and stearic acid tracers being oxidized, respectively.