title: Insulin-like growth factor-I, but not growth hormone, is dependent on a high protein intake to increase nitrogen balance in the rat.
abstract: The aim of the present study was to investigate the influence of dietary protein level on the protein anabolic effects of growth hormone (GH) and insulin-like growth factor-I (IGF-I). Female growing rats were fed on either a high- or a low-protein diet with crude protein contents of 222 and 83 g/kg respectively. The diets contained the same amount of metabolizable energy (15.1 MJ/kg) and were given during a 14 d period. During the same time, three groups of rats (n 8) on each diet received subcutaneous infusions of either saline, recombinant human GH (rhGH) or recombinant human IGF-I (rhIGF-I). rhGH and rhIGF-I were given in doses of 360 and 500 micrograms/d respectively. The low-protein diet alone reduced significantly (P < 0.05) IGF-I concentrations in serum and in tissue taken from the gastrocnemius muscle as well as IGF-I mRNA from the same muscle. The responses to rhGH and rhIGF-I in terms of muscle IGF-I and its mRNA were variable. However, when rhIGF-I was infused into rats on the high-protein diet, significantly elevated levels of IGF-I in muscle tissues could be observed. This was associated with a significantly (P < 0.05) increased N balance, whereas rhGH significantly (P < 0.05) enhanced the N balance in rats on the low-protein diet. Thus, it can be concluded that the level of dietary protein ingested regulates not only the effect of IGF-I on whole-body N economy but also the regulation of IGF-I gene expression in muscles. The exact mechanism by which GH exerts its protein anabolic effect, however, remains to be elucidated.
authors.affiliation: Department de Chemistry, Universidad Nacional de Colombia, Santafé de Bogotá, Colombia.
authors.forename: M
authors.initials: M
authors.lastname: Sánchez-Gómez
authors.forename: K
authors.initials: K
authors.lastname: Malmlöf
authors.forename: W
authors.initials: W
authors.lastname: Mejía
authors.forename: A
authors.initials: A
authors.lastname: Bermudez
authors.forename: M T
authors.initials: MT
authors.lastname: Ochoa
authors.forename: S
authors.initials: S
authors.lastname: Carrasco-Rodríguez
authors.forename: A
authors.initials: A
authors.lastname: Skottner
mesh_terms: D000818:Animals; D004044:Dietary Proteins / Q000008:administration & dosage*; D004734:Energy Metabolism; D005260:Female; D013006:Growth Hormone / Q000008:administration & dosage / Q000097:blood*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism*; D009132:Muscles / Q000187:drug effects / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000378:metabolism
chemical_list: D004044:Dietary Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D009584:Nitrogen