Iverson S J, Oftedal O T, Bowen W D, Boness D J, Sampugna J
Canadian Institute of Fisheries Technology, Technical University of Nova Scotia, Halifax.
J Comp Physiol B. 1995;165(1):1-12. doi: 10.1007/BF00264680.
Unlike most mammals, hooded seal (Cystophora cristata) pups are born with a substantial layer of adipose tissue. Subsequently, during the brief lactation period of only 4 days, fasting mothers mobilize enormous amounts of lipid from blubber and secrete milk (60% fat) at rates of 10 kg.day-1. Pups gain 7 kg.day-1 due primarily to the deposition of fat in blubber. We measured blubber content and fatty acid composition of blubber and milk in hooded seal mother-pup pairs at birth and over the 4-day lactation period to examine the nature and source of fetal lipids, the incorporation of maternal blubber fatty acids into milk lipid, and patterns of fatty acid deposition in suckling young. The fatty acid composition of the blubber of the newborn was notably different from that of its mother. Fetal deposition was likely due to a combination of both fetal synthesis and direct placental transfer of maternal circulating fatty acids. The blubber of the newborn was characterized by high levels (> 90% of total fatty acids) of saturated and monounsaturated fatty acids of primarily endogenous origin. In particular, the fetus appeared to have high delta-9 desaturase activity as evidenced by the large amounts of 14:1n-5 (4.2%) and 16:1n-7 (37.0%) in newborn blubber compared to maternal blubber (0.2% and 14.1%, respectively). Nevertheless, essential and long-chain polyunsaturated fatty acids of the n-3 and n-6 families, which could only have originated by direct transfer from the mother, comprised > 7% of pup blubber fatty acids and indicated greater rates of placental transfer than found in humans. In hooded seal mothers, rapid lipid transfer during the brief lactation period appeared to be facilitated by direct incorporation of mobilized fatty acids into milk. Although some differences in proportions of specific fatty acids were found between milk and maternal blubber, most of these differences declined over the course of lactation. However, selective mobilization of 20:5n-3 from maternal blubber into milk was apparent throughout lactation and resulted in elevated levels in pup blubber at weaning compared to maternal blubber. Ingested fatty acids were deposited directly and without modification into the blubber of pups, and by 4 days the fatty acid composition of pup blubber was virtually identical to that of the milk consumed.
与大多数哺乳动物不同，冠海豹（Cystophora cristata）幼崽出生时就有一层厚厚的脂肪组织。随后，在仅4天的短暂哺乳期内，禁食的母海豹会从鲸脂中动员大量脂质，并以10千克/天的速度分泌脂肪含量为60%的乳汁。幼崽每天增重7千克，这主要归功于脂肪在鲸脂中的沉积。我们测量了冠海豹母婴对出生时以及4天哺乳期内鲸脂的含量和脂肪酸组成，以及乳汁的脂肪酸组成，以研究胎儿脂质的性质和来源、母体鲸脂脂肪酸掺入乳汁脂质的情况，以及哺乳幼崽体内脂肪酸的沉积模式。新生幼崽鲸脂的脂肪酸组成与其母亲的明显不同。胎儿的脂肪沉积可能是胎儿合成和母体循环脂肪酸直接经胎盘转移共同作用的结果。新生幼崽的鲸脂特点是饱和脂肪酸和单不饱和脂肪酸含量很高（占总脂肪酸的90%以上），主要来源于内源性。特别是，胎儿似乎具有较高的δ-9去饱和酶活性，这从新生幼崽鲸脂中大量的14:1n-5（4.2%）和16:1n-7（37.0%）与母体鲸脂中的含量（分别为0.2%和14.1%）相比可以得到证明。然而，只能直接从母体转移而来的n-3和n-6系列必需脂肪酸和长链多不饱和脂肪酸，占幼崽鲸脂脂肪酸的比例超过7%，这表明胎盘转移的速率比人类更高。在冠海豹母亲中，短暂哺乳期内的快速脂质转移似乎是通过将动员的脂肪酸直接掺入乳汁来实现的。虽然乳汁和母体鲸脂中特定脂肪酸的比例存在一些差异，但这些差异在哺乳期过程中大多会减小。然而，在整个哺乳期内，20:5n-3从母体鲸脂中选择性地转移到乳汁中是很明显的，这导致断奶时幼崽鲸脂中的含量相对于母体鲸脂有所升高。摄入的脂肪酸直接沉积到幼崽的鲸脂中，没有发生变化，到4天时，幼崽鲸脂的脂肪酸组成实际上与所摄入乳汁的脂肪酸组成相同。
