Springfield College, Springfield, MA 01109, USA
Old Dominion University, Norfolk, VA 23529, USA.
J Exp Biol. 2018 Mar 7;221(Pt Suppl 1):jeb161554. doi: 10.1242/jeb.161554.
Animals that fast depend on mobilizing lipid stores to power metabolism. Northern elephant seals () incorporate extended fasting into several life-history stages: development, molting, breeding and lactation. The physiological processes enabling fasting and lactation are important in the context of the ecology and life history of elephant seals. The rare combination of fasting and lactation depends on the efficient mobilization of lipid from adipose stores and its direction into milk production. The mother elephant seal must ration her finite body stores to power maintenance metabolism, as well as to produce large quantities of lipid and protein-rich milk. Lipid from body stores must first be mobilized; the action of lipolytic enzymes and hormones stimulate the release of fatty acids into the bloodstream. Biochemical processes affect the release of specific fatty acids in a predictable manner, and the pattern of release from lipid stores is closely reflected in the fatty acid content of the milk lipid. The content of the milk may have substantial developmental, thermoregulatory and metabolic consequences for the pup. The lactation and developmental patterns found in elephant seals are similar in some respects to those of other mammals; however, even within the limited number of mammals that simultaneously fast and lactate, there are important differences in the mechanisms that regulate lipid mobilization and milk lipid content. Although ungulates and humans do not fast during lactation, there are interesting comparisons to these groups regarding lipid mobilization and milk lipid content patterns.
依赖于动员脂库为新陈代谢提供能量的禁食动物。北方象海豹（ ）将长时间禁食融入了几个生命史阶段：发育、换毛、繁殖和哺乳。使禁食和哺乳成为可能的生理过程在象海豹的生态学和生命史背景下非常重要。禁食和哺乳的罕见组合依赖于从脂肪组织中有效动员脂类并将其定向用于产奶。母象海豹必须合理利用她有限的身体储备来维持新陈代谢，同时生产大量富含脂肪和蛋白质的乳汁。身体储备中的脂类必须首先动员；脂肪分解酶和激素的作用刺激脂肪酸释放到血液中。生化过程以可预测的方式影响特定脂肪酸的释放，而脂库的释放模式在乳汁脂质的脂肪酸含量中得到了紧密反映。乳汁的含量可能对幼崽的发育、体温调节和新陈代谢产生重大影响。象海豹的泌乳和发育模式在某些方面与其他哺乳动物相似；然而，即使在同时禁食和泌乳的有限数量的哺乳动物中，调节脂类动员和乳脂含量的机制也存在重要差异。虽然有蹄类动物和人类在哺乳期不禁食，但在脂类动员和乳脂含量模式方面，与这些群体有一些有趣的比较。
