title: Time course of the GH/IGF axis response to fasting and increased ration in chinook salmon (Oncorhynchus tshawytscha).
abstract: Body growth in vertebrates is chiefly regulated by the GH/IGF axis. Pituitary growth hormone (GH) stimulates liver insulin-like growth factor-I (IGF-I) production. During fasting, plasma IGF-I levels decline due to the development of liver GH resistance, while GH levels generally increase. In mammals, decreased insulin during fasting is thought to cause liver GH resistance. However, the sequence of events in the GH/IGF axis response to fasting is not well characterized, especially in non-mammalian vertebrates. We assessed the time course of the GH/IGF axis response to fasting and increased ration in chinook salmon. Fish were placed on Fasting, Increased, or Control rations, and sampled daily for 4 days and at more widely spaced intervals through 29 days. Plasma IGF-I, GH, insulin, and 41 kDa IGF binding protein (putative salmon IGFBP-3), and liver IGF-I gene expression were measured. Control and Increased ration fish did not differ strongly. Plasma IGF-I and 41 kDa IGFBP were significantly lower in Fasted versus Control fish from day 4 onward, and liver IGF-I gene expression was significantly lower from day 6 onward. Liver IGF-I gene expression and plasma IGF-I levels were correlated. Plasma insulin was lower in Fasted fish from day 6 onward. There was a trend toward increased GH in Fasted fish on days 1-2, and GH was significantly increased Fasted fish from day 3 onward. Fasted GH first increased (days 1-3) to a plateau of 10-20 ng/ml (days 4-12) and then increased dramatically (days 15-29), suggesting that the GH response to fasting had three phases. The early increase in GH, followed by the decrease in plasma IGF-I after 4 days, suggests that GH resistance developed within 4 days.
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98195, USA. piercea@u.washington.edu
authors.forename: A L
authors.initials: AL
authors.lastname: Pierce
authors.forename: M
authors.initials: M
authors.lastname: Shimizu
authors.forename: B R
authors.initials: BR
authors.lastname: Beckman
authors.forename: D M
authors.initials: DM
authors.lastname: Baker
authors.forename: W W
authors.initials: WW
authors.lastname: Dickhoff
mesh_terms: D000818:Animals; D001835:Body Weight / Q000502:physiology; D005508:Food Deprivation / Q000502:physiology*; D013006:Growth Hormone / Q000097:blood / Q000378:metabolism*; D007328:Insulin / Q000097:blood / Q000378:metabolism; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D009752:Nutritional Status / Q000502:physiology; D009929:Organ Size / Q000502:physiology; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D012474:Salmon / Q000378:metabolism*
chemical_list: D007328:Insulin; D018972:Insulin-Like Growth Factor Binding Protein 3; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone