Enhanced aerobic capacities for fatty acid oxidation in the skeletal muscles of pinnipeds.

In an earlier study we showed that the skeletal muscles of pinnipeds (seals, sea lions and fur seals) have a high aerobic capacity. Their swimming muscles have volume densities of mitochondria 1.7 to 2.1 times greater than predicted values for the locomotory muscles of terrestrial mammals of comparable size. The purpose of this study was to assess the activity of citrate synthase (CS), the activity of -hydroxyacyl CoA dehydrogenase (HAD) and the concentration of myoglobin in pinnipeds. We used the CS:HAD ratio to asses the role of fatty acid oxidation in the total aerobic metabolism of these animals. Samples of swimming muscles and non-swimming muscles were collected from harbor seals (Phoca vitulina, n=37), Steller sea lions (Eumetopias jubatus, n=28) and northern fur seals (Callorhinus ursinus, n=5). The CS:HAD ratio in the swimming muscles was 0.7, 1.0 and 0.8 for the harbor seal, sea lion and fur seal, respectively. The concentration of myoglobin was 37.4 1.7, 28.1 1.6 and 22.6 2.5 mg/g wet mass muscle, respectively. These values were over an order of magnitude greater than those measured in the vastus medialis of the cotton rat (Sigmodon hispidus, n=5). The results agree with our previous results which indicated that pinnipeds have enhanced aerobic capacities and oxygen stores in their skeletal muscles. It indicates that the skeletal muscles of pinnipeds are metabolically poised for fatty acid oxidation even under the hypoxic conditions of diving.

Enhanced aerobic capacities for fatty acid oxidation in the skeletal muscles of pinnipeds. Academic Article