| Summary: | Rapid increases in body oxygen stores are a critical component of development in mammals that forage using breath-hold diving. In some pinniped species, they experience significant development of their oxygen stores during a post-weaning fasting period, without nutritional input. Important processes underlying the regulation of their blood oxygen stores during this period, including mobilization of stored iron and turnover of fetal erythrocytes, are not well understood. Previous studies have shown synthesis of tissuerespiratory pigments during development are concurrent with high levels of blood carbon monoxide (CO); suggestive of a large volume of heme turnover (a source of endogenous CO production) in deep-diving northern elephant seal pups. We measured a suite of analytes associated with blood oxygen stores, iron storage and mobilization, and heme degradation in longitudinal samples collected over 8 weeks of the post-weaning developmental fast in northern elephant seal pups. Milk samples were also measured to assess iron transfer rates from the mother to the pup prior to weaning. We examined changes across this period and associations among analytes to better understand how increases in hemoprotein production occurred alongside the process of heme degradation. Blood oxygen stores, serum markers of iron storage, and serum markers of heme degradation all increased throughout the fast. However, transferrin saturation and the total iron binding capacity of serum (the capacity for blood to bind iron to transferrin), remained constant. Estimates of iron transfer from mother to pup via lactation were not sufficient to account for estimates of iron needed for the magnitude of hemoprotein concentrations developed during the developmental fast suggesting fetal transfer and storage followed by subsequent mobilization. These patterns are consistent with rapid mobilization of stored tissue iron for erythropoiesis and heme synthesis concurrent with rapid degradation of existing heme and suggest stored iron reserves at ...
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