Repetitive stretch induces c-fos and myogenin mRNA within several hours in skeletal muscle removed from rats

Objective: To investigate what effect repetitive stretch has on gene transcription in muscle tissues removed from rats. Design: Case-control study. Setting: University laboratory. Animals: Eight female 8-week-old Wistar rats. Interventions: Rat anterior tibial and soleus muscles were removed and repetitively stretched about 20% of the muscle length by using the Magnus method in Krebs-Ringer solution. Stretch-relax cycles 15 times per minute were continued for 2 hours in 1 group and 4 hours in another group. Contralateral muscles removed from the same rat were incubated without stretch as the control. Main Outcome Measures: After repetitive stretch, total ribonucleic acid (RNA) was extracted from the muscles and Northern blotting was carried out using c-fos and myogenin oligonucleotide as probes. Results: Repetitive stretch during 2 hours significantly increased the expression of c-fos messenger RNA (mRNA) in both the tibialis anterior and soleus muscles. Increased expression of myogenin mRNA in both muscles was observed with repetitive stretch for 4 hours. Because of the initial increase of immediate early gene c-fos mRNA and the subsequent increase of myogenic transcription factor myogenin mRNA, it appears that repetitive muscle stretch induces sequential progression of gene transcription toward muscle hypertrophy. Conclusions: Mechanical repetitive stretch for a few hours would be one of the stimulating factors for muscle growth and should be available for muscle training in clinical rehabilitation.