Utilization of body energy reserves during work in dogs

¹ Quartermaster Food and Container Institute for the Armed Forces, Chicago, Illinois

Excretion of urinary nitrogen and acetone at rest and during four controlled levels of work output (treadmill running) was examined in five postabsorptive dogs. With resting energy-expenditures of 600–800 Cal., the average outputs of nonprotein nitrogen, urea nitrogen, creatine nitrogen, and acetone were 2.19 gm, 1.69 gm, 74.7 mg, and 11.6 mg, respectively. With the possible exception of acetone, output of the various urinary constituents was significantly higher (4 x) at rest than during work of comparable cost. Energy metabolism during the performance of 300, 600, 1200, and 1800 Cal. of work was estimated from the respiratory gas exchange and urinary nitrogen. During long-sustained physical work, the percentage of energy derived from the oxidation of carbohydrate, fat, and protein was relatively constant at 65, 32, and 3%, respectively. Preliminary calculations suggest that all of the energy, whether combusted as carbohydrate or fat, was derived ultimately from the body lipids.