Role of plasma and tissue lipids in the energy metabolism of the harbour seal

Abstract

Abstract Lipid is an important source of energy for harbour seals and other carnivorous marine mammals. This results primarily from their diet, which is rich in fish oil, and the large lipid stores in the blubber. Measurements of respiratory quotient (RQ) indicate that whole-body lipid catabolism provides 87% of metabolic energy for resting and 95% for exercising harbour seals. In earlier studies, we showed that the catabolism of plasma free fatty acids (FFA) provides only about 20% of total energy production in harbour seals. Recent studies indicate that very low density lipoprotein triglycerides (VLDL-TG) may provide an additional 13% of energy production in postabsorptive harbour seals. However, the catabolism of fatty acids from triglyceride-rich chylomicrons may increase fourfold after a meal and represent the primary source of lipid for energy metabolism during foraging dives. The third source of lipids is endogenous triglyceride stores in the tissues, especially skeletal muscle. Although studies to quantify the catabolism of endogenous tissue triglycerides are just beginning, the prospect of assembling a complete fuel budget for resting and exercising harbour seals appears good. This information will contribute to our understanding of how marine mammals partition oxygen and fuel reserves to maintain an aerobic, fat-based metabolism during most voluntary dives.