BIGA, PR; CAIN, KD; HARDY, RW; OVERTURF, K; OTT, TL; Marine Biological Laboratory, Woods Hole, MA; University of Idaho, Moscow, ID; University of Idaho, Moscow, ID; USDA, ARS, Hagerman, ID; University of Idaho, Moscow, ID: Growth hormone differentially regulates muscle myostatin-I and �II and increases circulating cortisol in rainbow trout (Oncorhynchus mykiss).

Myostatin negatively regulates muscle growth in vertebrates. Salmonids produce two myostatin transcripts from separate genes. Surprisingly, quantitative analyses indicate different regulatory mechanisms for the two myostatin genes in rainbow trout. Myostatin-I mRNA levels were elevated following recombinant bovine somatotropin (rbST) treatment, while myostatin-II mRNA levels were reduced compared to controls. In addition, cortisol levels in circulation were increased following rbST treatment compared to controls, and the pattern of change was positively correlated to myostatin-I mRNA levels. This is the first time a direct relationship has been reported between GH, cortisol, and myostatin. In addition, following rbST administration, myosin protein concentrations in skeletal muscle samples increased, suggesting that GH regulates expression of the most abundant muscle protein. These results indicate the two myostatin genes are differentially regulated and may possess different functions in rainbow trout muscle.