Effects of food intake on relaxin 3 (Rxn3) mRNA expression in the muscle of Atlantic salmon

The Rxn3 is a protein that belongs to the insulin‐like/relaxin superfamily and affect various physiological functions, including growth, food intake, and reproduction. Evidence in rodents suggests that Rxn3 is involved in the regulation of food intake and critical for proper development of muscle and bones. The roles that the insulin‐like/relaxin superfamily plays in regards to growth and metabolism is largely unknown in fish, including Atlantic salmon. Recently, we identified the mRNA sequence for the Atlantic salmon Rxn3 by screening the database using channel catfish insulin‐like 5 polypeptide mRNA sequence. Given the possible role of Rxn3 in muscle function and nutrient metabolism, changes in the expression of Rxn3 mRNA in response to the changes in food intake were examined. Juvenile Atlantic salmon (n=72, 6 fish per tank) were assigned to either receive food every day (control, n=4 tanks) or fasted for 14 days (fasted, n=4 tanks). Additionally, fish were fasted for 7 days and fed daily for the subsequent 7 days (refed, n=4 tanks). Muscle samples were collected from fish at the end of 14 days, and expression of Rx3 mRNA was measured using real‐time PCR. Expression of Rxn3 mRNA was similar among the three feeding treatments, suggesting that muscle expression of Rxn3 is not affected by changes in food intake. Given the preliminary nature of the study, further investigations are warranted to define the role of Rxn3 on the regulation of growth, food intake, and nutrient metabolism in Atlantic salmon. Support or Funding Information This project was partially funded by Kansas IDeA Network of Biomedical research Excellence (K‐INBRE) under the NIGMS/NIH grand P20GM103418.