| Summary: | Northern elephant seals are naturally adapted to prolonged periods (1–2 months) of absolute food and water deprivation (fasting). In terrestrial mammals, fasting stimulates ATP degradation and decreases ATP synthesis. Hypoxanthine‐guanine phosphoribosyl transferase (HGPRT) salvages ATP by recycling the purine degradation products derived from xanthine oxidase (XO) metabolism. The contributions of HGPRT to purine recycling during prolonged fasting in marine mammals are not well defined. In the present study, complete and partial HGPRT and XO cDNA sequences were obtained. Also, HGPRT and XO mRNA and protein expression was quantified in tissue from fasting elephant seals, along with the plasma levels of hypoxanthine (HX) and xanthine and activities of HGPRT and XO. Blood and tissue samples were collected from animals during the 1, 3, 5 and 7 week of their natural post‐weaning fast. The HGPRT and XO cDNA sequences encode proteins with conserved domains important for their function and regulation. HGPRT and XO mRNA and protein expression increased during the 7 wk in adipose tissue and muscle, respectively. Plasma xanthine and HX levels, and XO and HGPRT activities increased during the last two weeks of fasting. Results suggest that prolonged fasting in elephant seal pups is associated with increased capacity to recycle purines, which may contribute to enhancing the supply of ATP.
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