We sought to determine whether cyclooxygenase (COX) activity is necessary for overload-induced growth of adult rat skeletal muscle, and whether nitric oxide synthase (NOS) activity is involved in upregulation of COX messenger RNA (mRNA) expression in skeletal muscle.
Unilateral surgical removal of the gastrocnemius and soleus was performed on the right hindlimb of 16 female Sprague-Dawley rats (~230 g) to induce chronic overload (OL) of the plantaris for 14 d, with sham surgeries performed on the contralateral leg as a normally loaded (NL) control. Half of the rats were treated with the nonspecific COX inhibitor, ibuprofen (0.2 mg·mL−1 in drinking water; ~20 mg·kg−1·d−1). In a second experiment, the plantaris was unilaterally overloaded for 5 or 14 d in male rats (~350 g; N = 16 rats per time point) and half of the animals were treated with the NOS inhibitor, L-NAME (0.75 mg·mL−1 in drinking water; ~90 mg·kg−1·d−1).
Ibuprofen treatment inhibited plantaris hypertrophy by approximately 50% (P < 0.05) following 14 d of OL, as did L-NAME treatment (P < 0.05). COX-1 and COX-2 mRNA did not differ between any groups at 5 d. At 14 d, however, L-NAME caused a 30-fold increase in plantaris COX-1 mRNA expression independent of loading condition. Additionally, OL induced a 20-fold increase in COX-2 mRNA expression compared with NL (P < 0.05) at 14 d, without affecting COX-1 mRNA level. L-NAME treatment significantly inhibited OL-induced expression of COX-2 mRNA.
COX activity is important for in vivo muscle hypertrophy, and plantaris overload is associated with NOS activity-dependent COX-2 expression.
Center for Exercise Science, University of Florida, Gainesville, FL
Address for correspondence: David Criswell, P.O. Box 118206, Center for Exercise Science, University of Florida, Gainesville, FL 32611; E-mail: email@example.com.
Submitted for publication September 2005.
Accepted for publication December 2005.