Glucocorticoid receptor activation during exercise in muscle

Area of Science:

• Exercise Physiology
• Molecular Endocrinology
• Muscle Biology

Background:

• Glucocorticoid excess causes muscle atrophy.
• Endurance running is known to counteract this atrophy.
• The mechanism by which exercise affects glucocorticoid receptor (GR) activation remains unclear.

Purpose of the Study:

• To investigate if endurance running inhibits the activation of glucocorticoid-receptor complexes to a DNA-binding state.
• To determine the effect of exercise on the time-course of GR activation in different muscle types.
• To assess the influence of exercise on GR conformational changes.

Main Methods:

• Female adrenalectomized rats were injected with [3H]triamcinolone acetonide.
• Rats were either kept sedentary or subjected to immediate endurance running (23 m/min) for up to 90 minutes.
• Receptor activation was quantified using DNA-cellulose binding and DEAE-cellulose anion exchange chromatography.

Main Results:

• Receptor activation increased significantly over time in all studied muscles (fast-twitch red/white vastus lateralis, soleus, gastrocnemius, heart) in both sedentary and exercised rats.
• Exercise did not alter the time-course or the extent of GR activation.
• No inhibition or delay in the appearance of activated GR forms was observed due to exercise.

Conclusions:

• Glucocorticoid receptor activation in skeletal muscle is rapid and occurs independently of muscle fiber type.
• Exercise, within the tested parameters, does not inhibit the activation of glucocorticoid receptors.
• Longer exercise durations or additional training may be required to observe any potential inhibitory effects of exercise on GR activation.