Fuel homeostasis in the harbor seal during submerged swimming
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The turnover rates and oxidation rates of plasma glucose, lactate, and free fatty acids (FFA) were measured in three harbor seals (average mass=40 kg) at rest or during voluntary submerged swimming in a water flume at 35% (1.3 m·s-1) and 50% (2 m·s-1) of maximum oxygen consumption (MO2max).
For seals resting in water, the total turnover rates for glucose, lactate, and FFA were 23.2, 26.2, and 7.5 μmol·min-1·kg-1, respectively. Direct oxidation of these metabolites accounted for approximately 7%, 27%, and 33% of their turnover and 3%, 7%, and 18% of the total ATP production, respectively.
For swimming seals,MO2max was achieved at a drag load equivalent to a speed of 3 m·s-1 and averaged 1.85 mmol O2·min-1·kg-1, which is 9-fold greater than resting metabolism in water at 18°C.
At 35% and 50%MO2max, glucose turnover and oxidation rates did not change from resting levels. Glucose oxidation contributed about 1% of the total ATP production during swimming.
At 50%MO2max, lactate turnover and anaerobic ATP production doubled, but the steady state plasma lactate concentration remained low at 1.1 mM. Lactate oxidation increased 63% but still contributed only 4% of the total ATP production. Anaerobic metabolism contributed about 1% of the total ATP production at rest and during swimming.
The plasma FFA concentration and turnover rate inereased only 24% and 37% over resting levels, respectively, at 50%MO2max. However, the oxidation rate increased almost 3.5-fold and accounted for 85% of the turnover. The percentage of total ATP produced (21%) from FFA oxidation at 35% and 50%MO2max did not increase greatly over that at rest.
Dive duration decreased from 78 s while resting in water to 28 s at 50%MO2max.
The RQ ranged from 0.78 at rest to 0.74 at 50%MO2max, indicating that fat was an important source of energy during submerged swimming.
By adjusting breath-hold duration during strenuous underwater swimming, harbor seals are able to maintain an aerobic, fat-based metabolism.
Key wordsPhoca vitulina Swimming Metabolism Fuel
free fatty acid concentration
maximum oxygen consumption
carbon dioxid production
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