Developmental regulation of the activation of translation initiation factors of skeletal muscle in response to feeding in horses.

OBJECTIVE

To determine whether feeding-induced activation of translation initiation factors, specifically protein kinase B, ribosomal protein S6 kinase (S6K1), ribosomal protein S6 (rpS6), and eukaryotic initiation factor 4E binding protein 1, in horses is affected by age.

ANIMALS

6 yearlings, six 2-year-old horses, and 6 mature horses.

PROCEDURES

After an 18-hour period of feed withholding, horses consumed a high-protein meal (2 g/kg) at time 0 and 30 minutes (postprandial state) or continued to have feed withheld (postabsorptive state). Blood samples were collected for the duration of the experimental procedures and used to determine plasma concentrations of glucose, insulin, and amino acids. At 90 minutes, biopsy specimens were collected from a gluteal muscle and used to measure phosphorylation of translation initiation factors.

RESULTS

Plasma glucose, insulin, and amino acid concentrations were elevated for the postprandial state, compared with results for the postabsorptive state, regardless of age. Phosphorylation of protein kinase B, S6K1, rpS6, and eukaryotic initiation factor 4E binding protein 1 was increased for the postprandial state. There was an effect of age with increased phosphorylation of S6K1 at Thr(389) and rpS6 at Ser(235/236) in the yearlings and mature horses, compared with results for the 2-year-old horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Food consumption resulted in an increase in the activation of translation initiation factors, with the highest degree of responsiveness in the yearlings. This indicated that increased muscle accretion seen during growth could be a result of increased rates of muscle protein synthesis in response to a meal stimulus.