Published in:
01-04-2018
Sex Differences in the Associations between L-Arginine Pathway Metabolites, Skeletal Muscle Mass and Function, and their Responses to Resistance Exercise, in Old Age
Published in: The journal of nutrition, health & aging | Issue 4/2018
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Objectives
The current study was designed to explore the associations between L-arginine metabolites and muscle mass and function in old age, which are largely unknown.
Design
The study used a randomised, double-blind, placebo-controlled design.
Setting
The study was carried out in a laboratory setting.
Participants
50 healthy older adults [median age 70 years (IQR 67-73); 27 males].
Intervention
Participants undertook an 18-week resistance exercise program, and a nutritional intervention (fish oil vs. placebo).
Measurements
Serum homoarginine, ornithine, citrulline, asymmetric dimethylarginine (ADMA), NG-monomethyl-L-arginine (L-NMMA), and symmetric dimethylarginine (SDMA), maximal voluntary contraction (MVC) and isokinetic torque of the knee extensors at 30° s-1 (MIT), muscle cross sectional area (MCSA) and quality (MQ) were measured at baseline and after the intervention.
Results
No significant exercise-induced changes were observed in metabolite concentrations. There were significant sex differences in the associations between metabolites and muscle parameters. After adjusting for age, glomerular filtration rate and fish oil intervention, citrulline (P=0.002) and ornithine (P=0.022) were negatively associated with MCSA at baseline in males but not females. However, baseline citrulline was negatively correlated with exercise-induced changes in MVC (P=0.043) and MQ (P=0.026) amongst females. Furthermore, amongst males, baseline homoarginine was positively associated with exercise-induced changes in MVC (P=0.026), ADMA was negatively associated with changes in MIT (P=0.026), L-NMMA (p=0.048) and ornithine (P<0.001) were both positively associated with changes in MCSA, and ornithine was negatively associated with changes in MQ (P=0.039).
Conclusion
Therefore, barring citrulline, there are significant sex differences in the associations between L-arginine metabolites and muscle mass and function in healthy older adults. These metabolites might enhance sarcopenia risk stratification, and the success of exercise programs, in old age.