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Abstract: Seals and sea lions (pinnipeds) go through naturally occurring stages of nutrient restriction alternating with rapid weight gain. Recent work has focused on how pinnipeds manage fuel stores during periods of fasting, whereas the physiological management of weight gain has been less well-studied. Pinnipeds undergoing rehabilitation were used in a controlled setting to investigate the relationship of an important metabolic hormone, insulin, to mass gain and lipid deposition. Over two seasons, 16 rehabilitating harbor seal (Phoca vitulina) pups were monitored as they were fed a steady caloric intake. Plasma insulin levels, mass gain, and blubber deposition were measured over the 8-week rehabilitation period. Plasma insulin levels were low but increased significantly across the sampling stage and were positively related to blubber deposition and overall mass gain. These results indicate that despite low circulating levels, insulin may play a lipogenic role in seals and that insulin sensitivity may be an important labile physiological variable affecting lipid metabolism during different life history phases. Quantifying insulin sensitivity in blubber as well as additional mediators of lipogenesis such as adiponectin during rapid lipid accumulation will further elucidate the mechanisms by which pinnipeds modulate the relationship between insulin and lipid metabolism.
Key Words: lipid metabolism, insulin, harbor seal, Phoca vitulina
Page Numbers: 243-253