title: Effects of dietary protein on whole-body protein turnover and endocrine function in young-adult and aging dogs.
abstract: Thirty-six adult female Beagles averaging 2 (young-adult) or 8 (geriatric) yr of age were used to assess the effects of graded levels of dietary protein (16, 24, or 32%) on endocrine-controlled regulation of whole-body protein turnover. Rates of whole-body protein synthesis (WBPS) and whole-body protein degradation (WBPD) were estimated using orally administered 15N-glycine and total excreta collection. Although N balance was similar for all dogs, N flux through the metabolic pool increased linearly (P < 0.05) as protein intake increased. Rates of WBPS, WBPD, or the difference between them were not influenced by age (P > 0.10). A quadratic increase (P < 0.05) in WBPS and WBPD was observed in response to dietary protein. Serum insulin-like growth factor-I (IGF-I), IGF-I-binding protein 3, and total IGF-I-binding proteins were higher (P < 0.05) in geriatric dogs than in young-adult dogs regardless of protein intake. These results indicate that dietary protein in excess of 16% may not be required to maintain N balance in young-adult and aging dogs despite the linear increase in N flux through the metabolic pool. Furthermore, age-induced changes in endocrine functionality may differ between dogs and other species.
authors.affiliation: Department of Animal and Dairy Sciences, Auburn University, AL 36849, USA.
authors.forename: C C
authors.initials: CC
authors.lastname: Williams
authors.forename: K A
authors.initials: KA
authors.lastname: Cummins
authors.forename: M G
authors.initials: MG
authors.lastname: Hayek
authors.forename: G M
authors.initials: GM
authors.lastname: Davenport
mesh_terms: D000284:Administration, Oral; D000367:Age Factors; D000375:Aging / Q000378:metabolism*; D000596:Amino Acids / Q000097:blood; D000818:Animals; D004044:Dietary Proteins / Q000008:administration & dosage*; D004285:Dogs / Q000378:metabolism* / Q000502:physiology; D004703:Endocrine System / Q000502:physiology*; D005260:Female; D005934:Glucagon / Q000097:blood; D007328:Insulin / Q000097:blood; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D009584:Nitrogen / Q000008:administration & dosage / Q000378:metabolism; D009587:Nitrogen Isotopes; D011506:Proteins / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D004044:Dietary Proteins; D007328:Insulin; D018969:Insulin-Like Growth Factor Binding Proteins; D009587:Nitrogen Isotopes; D011506:Proteins; D007334:Insulin-Like Growth Factor I; D005934:Glucagon; D009584:Nitrogen