Sexually dimorphic effect of aging on skeletal muscle protein synthesis

Gordon I Smith,Kari T Chambers,Brian N Finck,Angela M Hall,Bettina Mittendorfer,Dominic N Reeds

doi:10.1186/2042-6410-3-11

Gordon I Smith, Kari T Chambers + Show 4 more

Open Access

https://doi.org/10.1186/2042-6410-3-11

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Abstract

BackgroundAlthough there appear to be no differences in muscle protein turnover in young and middle aged men and women, we have reported significant differences in the rate of muscle protein synthesis between older adult men and women. This suggests that aging may affect muscle protein turnover differently in men and women.MethodsWe measured the skeletal muscle protein fractional synthesis rate (FSR) by using stable isotope-labeled tracer methods during basal postabsorptive conditions and during a hyperaminoacidemic-hyperinsulinemic-euglycemic clamp in eight young men (25–45 y), ten young women (25–45 y), ten old men (65–85 y) and ten old women (65–85 y).ResultsThe basal muscle protein FSR was not different in young and old men (0.040 ± 0.004 and 0.043 ± 0.005%·h-1, respectively) and combined insulin, glucose and amino acid infusion significantly increased the muscle protein FSR both in young (to 0.063 ± 0.006%·h-1) and old (to 0.051 ± 0.008%·h-1) men but the increase (0.023 ± 0.004 vs. 0.009 ± 0.004%·h-1, respectively) was ~60% less in the old men (P = 0.03). In contrast, the basal muscle protein FSR was ~30% greater in old than young women (0.060 ± 0.003 vs. 0.046 ± 0.004%·h-1, respectively; P < 0.05) and combined insulin, glucose and amino acid infusion significantly increased the muscle protein FSR in young (P < 0.01) but not in old women (P = 0.10) so that the FSR was not different between young and old women during the clamp (0.074 ± 0.006%·h-1 vs. 0.072 ± 0.006%·h-1, respectively).ConclusionsThere is sexual dimorphism in the age-related changes in muscle protein synthesis and thus the metabolic processes responsible for the age-related decline in muscle mass.

Highlights

There appear to be no differences in muscle protein turnover in young and middle aged men and women, we have reported significant differences in the rate of muscle protein synthesis between older adult men and women
We hypothesized that: i) the anabolic response to increased amino acid and insulin availability would be reduced in old compared with young subjects, ii) the age-related decline in the anabolic response would be greater in women than in men, and iii) the basal rate of muscle protein synthesis would be greater in old compared with young women
Glucose and amino acid concentrations Plasma testosterone concentration was significantly greater in men than women (P < 0.001) and was not affected by aging (Table 1)

Summary

Introduction

There appear to be no differences in muscle protein turnover in young and middle aged men and women, we have reported significant differences in the rate of muscle protein synthesis between older adult men and women. We found that obese, old women, but not obese, old men, failed to significantly increase the rate of muscle protein synthesis in response to mixed meal ingestion [12]. This suggests that differences in muscle protein turnover between men and women might be most apparent when muscle mass is changing (i.e., during aging vs earlier adulthood when muscle mass is steady) and that aging affects muscle protein turnover differently in men and women. Hypoandrogenemia is associated with a reduced lean body mass [14] and treatment with testosterone increases the muscle protein synthesis rate [15,16,17,18,19,20]

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