AJP - Endocrinology and Metabolism, Vol 247, Issue 5 597-E603, Copyright © 1984 by American Physiological Society
Androgen cytosol binding in exercise-induced sparing of muscle atrophy
R. C. Hickson, T. T. Kurowski, J. A. Capaccio and R. T. Chatterton Jr
This study was undertaken to determine whether the exercise-induced sparing
of glucocorticoid-induced muscle atrophy is related to increased androgen
cytosol binding. Female rats were divided into a sedentary or an exercise
group that was trained by treadmill running 100 min/day for 13-15 wk.
During the last 12 days of training, each of these groups was further
subdivided into groups that received daily subcutaneous injections of
cortisone acetate (CA) (100 mg/kg body wt) or the vehicle 1% carboxymethyl
cellulose. Exercise prevented 30-40% of the weight loss due to CA treatment
in gastrocnemius and plantaris muscles. Scatchard analyses of specific
binding of [3H]methyltrienolone (R1881), a synthetic androgen that binds to
androgen receptors, were nonlinear in muscles from vehicle-treated
sedentary and trained rats and were resolved by a two-component binding
model. The lower affinity component, which was attributed to a
glucocorticoid receptor, disappeared in muscles of glucocorticoid-treated
animals as evidenced by linear Scatchard plots. Receptor concentrations of
the androgenic component of [3H]methyltrienolone binding were similar in
gastrocnemius and plantaris muscles in all treatment groups. In binding
specificity studies of gastrocnemius muscles, the relatively high
competition by various glucocorticoids and progesterone for
[3H]methyltrienolone binding in the vehicle-treated groups was reduced by
CA treatment. The lack of change in androgen cytosol receptor levels
suggests that this is not a mechanism by which exercise protects against
glucocorticoid-induced muscle atrophy.
