title: Prolonged fasting increases purine recycling in post-weaned northern elephant seals.
abstract: Northern elephant seals are naturally adapted to prolonged periods (1-2 months) of absolute food and water deprivation (fasting). In terrestrial mammals, food deprivation stimulates ATP degradation and decreases ATP synthesis, resulting in the accumulation of purines (ATP degradation byproducts). Hypoxanthine-guanine phosphoribosyl transferase (HGPRT) salvages ATP by recycling the purine degradation products derived from xanthine oxidase (XO) metabolism, which also promotes oxidant production. The contributions of HGPRT to purine recycling during prolonged food deprivation in marine mammals are not well defined. In the present study we cloned and characterized the complete and partial cDNA sequences that encode for HGPRT and xanthine oxidoreductase (XOR) in northern elephant seals. We also measured XO protein expression and circulating activity, along with xanthine and hypoxanthine plasma content in fasting northern elephant seal pups. Blood, adipose and muscle tissue samples were collected from animals after 1, 3, 5 and 7 weeks of their natural post-weaning fast. The complete HGPRT and partial XOR cDNA sequences are 771 and 345 bp long and encode proteins of 218 and 115 amino acids, respectively, with conserved domains important for their function and regulation. XOR mRNA and XO protein expression increased 3-fold and 1.7-fold with fasting, respectively, whereas HGPRT mRNA (4-fold) and protein (2-fold) expression increased after 7 weeks in adipose tissue and muscle. Plasma xanthine (3-fold) and hypoxanthine (2.5-fold) levels, and XO (1.7- to 20-fold) and HGPRT (1.5- to 1.7-fold) activities increased during the last 2 weeks of fasting. Results suggest that prolonged fasting in elephant seal pups is associated with increased capacity to recycle purines, which may contribute to ameliorating oxidant production and enhancing the supply of ATP, both of which would be beneficial during prolonged food deprivation and appear to be adaptive in this species.
authors.affiliation: School of Natural Sciences, University of California, Merced, 5200 North Lake Road, Merced, CA 95343, USA. jorganis@ucmerced.edu
authors.forename: José Guadalupe
authors.initials: JG
authors.lastname: Soñanez-Organis
authors.forename: José Pablo
authors.initials: JP
authors.lastname: Vázquez-Medina
authors.forename: Tania
authors.initials: T
authors.lastname: Zenteno-Savín
authors.forename: Andres
authors.initials: A
authors.lastname: Aguilar
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Crocker
authors.forename: Rudy M
authors.initials: RM
authors.lastname: Ortiz
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002140:California; D003001:Cloning, Molecular; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000378:metabolism; D005508:Food Deprivation; D015971:Gene Expression Regulation, Enzymologic; D007041:Hypoxanthine Phosphoribosyltransferase / Q000097:blood / Q000378:metabolism; D008969:Molecular Sequence Data; D011687:Purines / Q000737:chemistry* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D046048:Seals, Earless; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014969:Xanthine Oxidase / Q000097:blood / Q000378:metabolism
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D011687:Purines; D012333:RNA, Messenger; D000255:Adenosine Triphosphate; D014969:Xanthine Oxidase; D007041:Hypoxanthine Phosphoribosyltransferase