Table 3.
Muscle protein metabolism
| Adult | Old | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 25% AA/protein | 0% AA/protein | 25% AA/protein | 0% AA/protein | Analysis of variance, significant effects | ||||||||
| C | INS– | AA– | INS–/AA– | C | INS– | AA– | INS–/AA– | RSE | A | M | I | |
| Gastrocnemius | ||||||||||||
| Protein concentration (mg (g tissue)−1) | 199 | 205 | 200 | 203 | 194 | 192c | 196 | 194c | 8 | < 0.002 | n.s. | n.s. |
| RNA concentration (mg (g tissue)−1) | 0.99 | 0.97 | 0.97 | 0.99 | 1.05 | 1.05c | 1.04c | 1.04 | 0.06 | < 0.001 | n.s. | n.s. |
| Capacity for protein synthesis (mg RNA (g protein)−1) | 4.97 | 4.74 | 4.83 | 4.89 | 5.44c | 5.46c | 5.32c | 5.39c | 0.34 | < 0.0001 | n.s. | n.s. |
| Ribosomal efficiency (mg protein synthesized (mg RNA)−1 day−1) | 7.99 | 4.16b | 6.91 | 4.33b | 6.69c | 3.78b | 6.86 | 3.80b | 0.92 | < 0.03 | n.s. | < 0.0001 |
| Absolute synthesis rates (mg protein synthesized day−1) | 21.19 | 10.61b | 18.3 | 11.41b | 18.25 | 10.75b | 18.08 | 10.25b | 3.05 | n.s. | n.s. | < 0.0001 |
| Soleus | ||||||||||||
| Protein concentration (mg (g tissue)−1) | 185 | 185 | 182 | 184 | 179 | 178 | 177 | 174c | 8 | < 0.002 | n.s. | n.s. |
| RNA concentration (mg (g tissue)−1) | 1.61 | 1.66 | 1.62 | 1.57 | 1.53 | 1.43c | 1.49c | 1.57 | 0.10 | < 0.001 | n.s. | n.s. |
| Capacity for protein synthesis (mg RNA (g protein)−1) | 8.69 | 8.99 | 8.94 | 8.53 | 8.60 | 8.11 | 8.43 | 8.99 | 0.61 | n.s. | n.s. | n.s. |
| Ribosomal efficiency (mg protein synthesized (mg RNA)−1 day−1) | 7.70 | 5.71b | 7.28 | 5.54b | 7.17 | 5.67b | 7.48 | 5.54b | 0.68 | n.s. | n.s. | < 0.0001 |
| Absolute synthesis rates (mg protein synthesized day−1) | 4.63 | 3.46b | 4.74 | 3.39b | 4.75 | 3.62b | 4.94 | 3.60b | 0.59 | n.s. | n.s. | < 0.0001 |
Characteristics of gastrocnemius and soleus protein metabolism were measured in adult and old rats in the four groups: C, INS−, AA–, INS–/AA–. Protein synthesis was measured using the l-[13C]valine flooding dose. Ten rats were used to measure basal protein-bound valine enrichment. Values are means and residual s.e.m. (RSE), n = 6–8. Three-way analyses of variance were performed to discriminate among effects of age (A), type of meal (M), insulin (I), on gastrocnemius and soleus protein metabolism. n.s., not significant. No interaction between the effect of age, insulin secretion state and amino acid/protein meal was significant.
P < 0.05 AA–versus C and INS–/AA–versus INS−.
P < 0.05 INS−versus C and INS–/AA–versus AA–.
P < 0.05versus adult rats in the corresponding groups.