Journal
JOURNAL OF CLINICAL ENDOCRINOLOGY & METABOLISM
Volume 91, Issue 8, Pages 3024-3033Publisher
ENDOCRINE SOC
DOI: 10.1210/jc.2006-0357
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Funding
- NCRR NIH HHS [RR 011145] Funding Source: Medline
- NIA NIH HHS [1R01 AG 14369-01] Funding Source: Medline
- NIDDK NIH HHS [1R01 DK 070534, 2R01 DK 49296-08, 1R01 DK 59627] Funding Source: Medline
- NIGMS NIH HHS [5S06 GM 068510] Funding Source: Medline
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Objective: In this study, we determined the effects of graded doses of testosterone on muscle fiber cross-sectional area (CSA) and satellite cell number and replication in older men. Participants: Healthy men, 60 - 75 yr old, received a long-acting GnRH agonist to suppress endogenous testosterone production and 25, 50, 125, 300, or 600 mg testosterone enanthate im weekly for 20 wk. Methods: Immunohistochemistry, light and confocal microscopy, and electron microscopy were used to perform fiber typing and quantitate myonuclear and satellite cell number in vastus lateralis biopsies, obtained before and after 20 wk of treatment. Results: Testosterone administration in older men was associated with dose-dependent increases in CSA of both types I and II fibers. Satellite cell number increased dose dependently at the three highest doses (3% at baseline vs. 6.2, 9.2, and 13.0% at 125, 300, and 600 mg doses, P < 0.05). Testosterone administration was associated with an increase in the number of proliferating cell nuclear antigen + satellite cells (1.8% at baseline vs. 3.9, 7.5, and 13% at 125, 300, and 600 mg doses, P < 0.005). The expression of activated Notch, examined only in the 300-mg group (baseline, 2.3 vs. 9.0% after treatment, P < 0.005), increased in satellite cells after testosterone treatment. The expression of myogenin (baseline, 6.2 vs. 20.7% after treatment, P < 0.005), examined only in the 300-mg group, increased significantly in muscle fiber nuclei after testosterone treatment, but Numb expression did not change. Conclusions: Older men respond to graded doses of testosterone with a dose-dependent increase in muscle fiber CSA and satellite cell number. Testosterone-induced skeletal muscle hypertrophy in older men is associated with increased satellite cell replication and activation.
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