Co-ingestion of carbohydrate and whey protein increases fasted rates of muscle protein synthesis immediately after resistance exercise in rats

Abstract

The objective of the study was to investigate whether co-ingestion of carbohydrate and protein as compared with protein alone augments muscle protein synthesis (MPS) during early exercise recovery. Two months old rats performed 10 repetitions of ladder climbing with 75% of body weight attached to their tails. Placebo (PLA), whey protein (WP), or whey protein plus carbohydrate (CP) was then given to rats by gavage. An additional group of sedentary rats (SED) was used as controls. Blood samples were collected immediately and at either 1 or 2 h after exercise. The flexor hallucis longus muscle was excised at 1 or 2 h post exercise for analysis of MPS and related signaling proteins. MPS was significantly increased by CP compared with PLA (p<0.05), and approached significance compared with WP at 1 h post exercise (p = 0.08). CP yielded a greater phosphorylation of mTOR compared with SED and PLA at 1 h post exercise and SED and WP at 2 h post exercise. CP also increased phosphorylation of p70S6K compared with SED at 1 and 2 h post exercise. 4E-BP1 phosphorylation was inhibited by PLA at 1 h but elevated by WP and CP at 2 h post exercise relative to SED. The phosphorylation of AMPK was elevated by exercise at 1 h post exercise, and this elevated level was sustained only in the WP group at 2 h. The phosphorylation of Akt, GSK3, and eIF2Bε were unchanged by treatments. Plasma insulin was transiently increased by CP at 1 h post exercise. In conclusion, post-exercise CP supplementation increases MPS post exercise relative to PLA and possibly WP, which may have been mediated by greater activation of the mTOR signaling pathway.

Fig 1. Muscle protein synthesis.

(A) Quantification of puromycin-labeled peptide, expressed as a percentage of a standard sample obtained from a post exercised rat muscle. (B) Representative image of western blot analysis for puromycin using a charge-coupled device camera. For Fig 1B, each column is a western blot from a different rat randomly selected. (C) Free puromycin concentration measured as described. (D) Muscle protein synthesis expressed using the value of puromycin labeled peptides relative to the free puromycin concentration in the same sample. All values are mean ± SEM (n = 10 per group). †, p<0.05 vs. PLA. ‡, p<0.05 vs. 1 h.

Fig 2. The phosphorylation of mTOR signaling pathways.

(A) mTOR phosphorylation at Ser²⁴⁴⁸ expressed as a percentage of a standard sample obtained from an insulin-stimulated rat tissue. (B) p70S6k phosphorylation at Thr³⁸⁹expressed as a percentage of a standard sample obtained from an insulin-stimulated rat tissue. (C) rpS6 phosphorylation at Ser²³⁶ expressed as a percentage of a standard sample obtained from an insulin-stimulated rat tissue. (D) 4E-BP1 phosphorylation expressed as a percentage of the gamma isoform. All values are mean ± SEM (n = 10 per group).*, p<0.05 vs. SED. †, p<0.05 vs. PLA. §, p<0.05 vs. WP. ‡, p<0.05 vs. 1 h.

Fig 3. The phosphorylation of Akt-GSK signaling pathways.

(A) Akt phosphorylation at Ser⁴⁷³ expressed as a percentage of a standard sample obtained from insulin-stimulated rat tissue. (B) GSK3β phosphorylation at Ser⁹ expressed as a percentage of a standard sample obtained from insulin-stimulated rat tissue. (C) GSK3α phosphorylation at Ser²¹expressed as a percentage of a standard sample obtained from insulin-stimulated rat tissue. (D) eIF2Bε phosphorylation at Ser⁵³⁹expressed as a percentage of a standard sample obtained from insulin-stimulated rat tissue. All values are mean ± SEM (n = 10 per group).

Fig 4. The phosphorylation of AMPK-FOXO3A signaling pathways.

(A) AMPK phosphorylation at Thr¹⁷² expressed as a percentage of a standard sample obtained from an insulin-stimulated rat tissue. (B) FOXO3A phosphorylation at Ser^318/321 expressed as a percentage of a standard sample obtained from an insulin-stimulated rat tissue. All values are mean ± SEM (n = 10 per group).*, p<0.05 vs. SED. §, p<0.05 vs. WP. ‡, p<0.05 vs. 1 h.