Continuous and pulsed ultrasound do not increase heat shock protein 72 content

Therapeutic ultrasound (US) is a common treatment used in the rehabilitation of injured muscle. To determine whether therapeutic US could increase the content of heat shock protein (HSP) 72 in skeletal muscle, male Sprague-Dawley rats were anesthetized and the muscles from one hind limb treated with 15 min of US at 1 MHz using either: 1. continuous US at 1.0 W/cm(2), 2. pulsed US at 2.0 W/cm(2) at 50% duty cycle, or 3. pulsed US at 1.0 W/cm(2) at 20% duty cycle. All treatments were applied using a transducer (1.6-cm diameter) on an area of the rat hind limb twice the size of the sound head. At 24 h following treatment, the plantaris, soleus, white and red gastrocnemius muscles were removed and assessed for HSP 72 content by Western blotting. No significant increases in HSP 72 content were detected in any of the muscles examined following any US treatment. These results suggest muscle HSP content is not elevated following a typical therapeutic dose of either continuous or pulsed US in the rat.