Regulation of energy metabolism during social interactions in rainbow trout: A role for AMP-activated protein kinase

Rainbow trout (Oncorhynchus mykiss) confined in pairs form social hierarchies in which subordinate fish typically experience fasting and high circulating cortisol levels, resulting in low growth rates. The present study investigated the role of AMP-activated protein kinase (AMPK) in mediating metabolic adjustments associated with social status in rainbow trout. After 3 d of social interaction, liver AMPK activity in subordinate trout was significantly higher than that of dominant or sham (fish handled in the same fashion as paired fish but held individually) trout. Elevated liver AMPK activity in subordinate fish likely reflected a significantly higher ratio of phosphorylated AMPK (phospho-AMPK) to total AMPK protein, which was accompanied by significantly higher AMPKα1 relative mRNA abundance. Liver ATP and creatine phosphate (CrP) concentrations in subordinate fish also were elevated, perhaps as a result of AMPK activity. Sham fish that were fasted for 3 d exhibited effects parallel to those of subordinate fish, suggesting that low food intake was an important trigger of elevated AMPK activity in subordinate fish. Effects on white muscle appeared to be influenced by the physical activity associated with social interaction. Overall, muscle AMPK activity was significantly higher in dominant and subordinate trout than sham fish. Muscle phospho-AMPK:total AMPK protein abundance was highest in subordinate fish, while muscle AMPKα1 relative mRNA abundance was elevated by social dominance. Muscle ATP and CrP concentrations were high in dominant and subordinate fish at 6 h of interaction, decreasing significantly thereafter. Collectively, the findings of the present study support a role for AMPK in mediating the liver and white muscle metabolic adjustments associated with social hierarchy formation in rainbow trout.

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