Houser Dorian S, Crocker Daniel E
Department of Biology, School of Science and Technology, Sonoma State University, 1801 East Cotati Avenue, Rohnert Park, CA, 94928, USA.
Physiol Biochem Zool. 2004 Sep-Oct;77(5):838-46. doi: 10.1086/422055.
Long-term fasting is a component of northern elephant seal (Mirounga angustirostris) life history requiring physiological adaptations to nitrogen conservation. Plasma free amino acids (FAAs) were determined for five elephant seal pups during the second and eighth weeks of the postweaning fast, six lactating female seals at 4-6 and 25 d postpartum, and seven sexually competitive adult male seals taken midway through the breeding season. Total FAAs declined in lactating females (11%) and pups (30%) with time fasting, but cystine concentration more than doubled in pups while decreasing by approximately 43% in lactating females. Methionine concentration significantly increased (approximately 68%) across lactation in adult females but was low for all classes of seal. Alanine was the most abundant FAA in adult males, and glycine became the dominant FAA in adult females late in lactation. Glutamine dominated the FAAs of weaned pups across the fast. Reductions in total FAAs of weanlings mirrored reductions in protein catabolism, but reductions in total FAAs also occurred in lactating females concomitant with an increase in protein catabolism. Observed variation in FAA concentrations may reflect ontogenetic requirements for certain amino acids in fasting weanlings. Similarly, increases in specific FAA concentrations across lactation may reflect variations in FAA flux resulting from the nutrient demands of lactogenesis.
长期禁食是北象海豹（Mirounga angustirostris）生活史的一个组成部分，需要生理上适应氮的保存。在断奶后禁食的第二周和第八周，对五只象海豹幼崽进行了血浆游离氨基酸（FAA）测定；在产后4 - 6天和25天，对六只哺乳期雌性海豹进行了测定；在繁殖季节中期，对七只具有性竞争力的成年雄性海豹进行了测定。随着禁食时间的延长，哺乳期雌性海豹（下降11%）和幼崽（下降30%）的总FAA浓度均下降，但幼崽的胱氨酸浓度增加了一倍多，而哺乳期雌性海豹的胱氨酸浓度下降了约43%。成年雌性海豹在整个哺乳期蛋氨酸浓度显著增加（约68%），但所有类别的海豹蛋氨酸浓度都较低。丙氨酸是成年雄性海豹中含量最丰富的FAA，在哺乳期后期，甘氨酸成为成年雌性海豹中占主导地位的FAA。在整个禁食过程中，谷氨酰胺在断奶幼崽的FAA中占主导地位。断奶幼崽总FAA浓度的降低反映了蛋白质分解代谢的减少，但哺乳期雌性海豹的总FAA浓度也出现了下降，同时蛋白质分解代谢增加。观察到的FAA浓度变化可能反映了禁食断奶幼崽对某些氨基酸的个体发育需求。同样，整个哺乳期特定FAA浓度的增加可能反映了泌乳营养需求导致的FAA通量变化。
