Age, Sex, and Reproductive State Influence Free Amino Aid Concentrations in the Fasting elephant seal.

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 ~43% in lactating females. Methionine concentration significantly increased (~68%) across lactation in adult females but was low for all males, and glycine became the dominant FAA in adult females late in lactation. Glutamine dominated the FAAs of the weaned pups across the fast. Reductions in the total FAAs of weanlings mirrored the 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 nutrient demands of lactogenesis.