The “muscle‐full” anabolic set‐point in response to oral protein is lower in muscle of older men than in young men

We previously showed that muscle anabolic responses to i.v. essential amino acids or oral protein bolus are brief (~1.5 h) but large (~3‐fold) in young men. We predicted that in older men anabolic responses would also be brief and blunted compared to those in younger men, even with supply of a ‘high‐quality’ protein bolus. Four men (~67 y, BMI ~25 kg.m −2 ) received [1,2‐ 13 C 2 ]leucine (1mg.kg.h −1 ) over 6.5 h, the first 2.5 h being before drinking 48 g whey suspension; muscle was intermittently biopsied. Myofibrillar protein synthesis (MPS) was measured as a capture of [1,2‐ 13 C 2 ]leucine and signaling by immunoblotting. MPS increased 0–45 min after whey (0.034±0.008 to 0.059±0.008.%.h −1 ; P <0.05). However, whereas MPS fell thereafter, anabolic signals remained elevated e.g. increased phosphorylation of p70S6 kinase Th389 present from 45 min persisted at 180 min (+130±17%; P <0.01). Notably, when compared to our previous results in younger men, both peak (0.10±0.01 vs. 0.059±0.008.%.h −1 ; P <0.01) and area under the curve analyses (0.089±0.019 vs. 0.034 ±0.004 %.h −1 ; P <0.01) demonstrated that MPS responses to oral protein were blunted in older men. We conclude that MPS responses to oral protein are more short‐lived in older men than in the young and also that as in young men, anabolic signals outlast them. Moreover, generous leucine availability (~6 g) did not overcome anabolic blunting previously observed. Support: RCUK