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|Nutritional Stress and Hormone Regulation of Growth in Fish: Fasting Modulates GH Stimulation of Liver IGF-1 in a Pacific Rockfish
|Presenting Author Name
|Presenting Author Affiliation
|Cal Poly, San Luis Obispo
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Growth hormone (GH) regulates growth in fishes by stimulating the liver to synthesize and release the hormone insulin-like growth factor-1 (IGF-1), which then promotes muscle and bone growth. Fish experiencing conditions of food limitation, however, can have elevated blood GH even with low IGF-1 and slow growth, suggesting that nutritional stress may cause changes in liver sensitivity to GH. Here, we examined how food deprivation (fasting) affected GH induction of liver IGF-1 in juvenile Gopher Rockfish (Sebastes carnatus), as part of a larger project examining IGF-1 as a growth rate biomarker in Pacific rockfishes. Juvenile Gopher Rockfish were fed or fasted for 14 d and then treated with recombinant Sea Bream GH or saline (control). GH treatment elevated liver IGF-1 mRNA levels in fed fish, but failed to alter IGF-1 gene expression in fasted fish. Fasted fish also showed reduced liver gene transcript abundance for GH receptors, and reduced mRNA levels for several intracellular proteins involved in GH induction of liver IGF-1 synthesis including STAT5b and HNF3β. The phosphorylation levels of JAK2 and STAT5b, two proteins key to IGF-1 synthesis, were 2-fold and 2.4-fold, respectively, in fed fish compared to fasted fish. Together, these findings indicate that food deprivation downregulates gene pathways critical for GH stimulation of IGF-1 production including liver GH receptor expression and parts of the intracellular transduction pathway for GH stimulation of IGF-1 synthesis, and suggest liver GH resistance as one mechanism underlying the reduced growth of fish during nutritional stress.