Meeting Abstract

P1.33  Tuesday, Jan. 4  Differential Effects of Growth Hormone on the Expression of Insulin-like Growth Factors 1 and 2 WALOCK, C.N.*; MARTIN, L.E.; KITTILSON, J.D.; SHERIDAN, M.A.; North Dakota St. Univ, Fargo chad.walock@ndsu.edu

The growth of vertebrates is primarily controlled by the growth hormone (GH)-insulin-like growth factor (IGF) system. In mammals, postembryonic growth is mediated by IGF-1 produced under the influence of GH, whereas embryonic growth is mediated by IGF-2, the production of which is not influenced by GH. Recent reports of the IGF-2 expression in tissues of juvenile and adult fish suggest that it may play a role in regulating post-embryonic growth in this group. In this study, we used juvenile (postembryonic) rainbow trout to examine the influence of GH on the expression of IGF-1 and IGF-2 mRNAs and to assess the mechanism(s) through which GH exerts its actions. Fish were implanted with mini osmotic pumps containing GH or saline for 21 days. GH significantly increased mRNA levels of IGF-1 and IGF-2 in both liver and muscle of levels observed in saline-implanted fish. The direct effects of GH were assessed on isolated hepatocytes incubated in vitro. GH stimulated expression of IGF-1 and IGF-2 mRNAs in a concentration- and time-related manner; GH was more potent and more efficacious in stimulating IGF-2 expression than IGF-1 expression. The ERK pathways inhibitor, U0126, and the PI3K/Akt pathway inhibitor, LY294002, blocked GH-stimulated IGF-1 and IGF-2 expression. These findings indicate that GH stimulates IGF-2 expression to a greater extent than IGF-1 expression and support a role of IGF-2 in postembryonic growth of fish. These findings also indicate that GH-stimulated IGF-1 and IGF-2 expressed involve activation of the ERK and PI3K/Akt signaling pathways. (Supported by NSF IOS 0920116)