The increase in Akt phosphorylation following feeding is independent of age in growing and mature Thoroughbred mares

Abstract

The activation of the initiation factors for protein synthesis in skeletal muscle has been shown to increase following consumption of a protein‐containing meal due to increases in both insulin (INS) and amino acid (AA) concentrations. In neonates, INS sensitivity has been shown to decrease with age, reducing the downstream signalling of Akt and resulting in lower skeletal muscle protein synthesis. The objective of this study was to determine the effects of an 18h period of feed witholding, both with (postprandial; PP) and without (post‐absorptive; PA) the re‐feeding of a high protein meal, on the activation of Akt in gluteal muscle of yearling, 2y old, and mature Thoroughbred mares (N=18). Blood samples were taken throughout the experimental period to measure plasma AA via HPLC. A gluteal muscle biopsy was taken after the last blood sample (t = 90 min) to measure the phosphorylation (P) of Akt at Ser473 and Thr308 using Western blotting techniques. For all horses, indispensible AA were ~ 25‐ 110% higher in the PP versus the PA period (P< 0.0001). There was a significant increase in Akt P‐Ser473 (P< 0.0001) and a trend for higher AktP‐Thr308 (P= 0.09) in the PP relative to PA state. Age did affect on the Akt phosphorylation (P > 0.05). Consumption of a high protein meal, following feed withholding, appeared to activate Akt in adolescent and mature horses. Additional research is necessary to determine whether the increase in Akt phosphorylation corresponded to an increase in the phosphorylation of downstream translation initiation factors. Funded by the Department of Animal and Food Sciences.