Androgen receptor in rat skeletal muscle: characterization and physiological variations

Area of Science:

• Endocrinology
• Molecular Biology
• Muscle Physiology

Background:

• Androgen effects on skeletal muscle are significant but cellular mechanisms remain incompletely understood.
• Investigating androgen receptor presence and characteristics in muscle tissue is crucial for elucidating androgen action.

Purpose of the Study:

• To characterize androgen binding and receptor specificity in rat skeletal muscle (quadriceps femoris).
• To determine the concentration and regulation of androgen receptors in skeletal muscle.

Main Methods:

• Hormone-receptor complex analysis using radiolabeled steroids ([3H]testosterone, [3H]androstanolone, [3H]methyltrienolone, [3H]estradiol).
• Scatchard plot analysis for binding affinity and competition assays with various steroids and anti-androgens.
• Measurement of receptor concentration in cytosol preparations from castrated and testosterone-treated rats.

Main Results:

• Androgen receptor in skeletal muscle exhibits identical specificity to other target tissues, binding testosterone and androstanolone with high affinity.
• Progesterone, cyproterone acetate, and spironolactone competed for binding, while estrogens and cortisol did not.
• Receptor concentration in adult male rat cytosol was low (1 fmol/mg protein) but increased significantly after testosterone treatment.
• Extensive steroid metabolism in cytosol necessitated the use of enzyme-free preparations for accurate binding studies.

Conclusions:

• Skeletal muscle possesses specific androgen-binding sites, confirming the presence of androgen receptors.
• Despite low concentrations, the observed specificity and androgen regulation suggest a direct cellular role for androgens in skeletal muscle.
• These findings support the hypothesis that androgens can directly impact skeletal muscle function at the cellular level via receptor-mediated pathways.