Synergistic tenotomy: effect on chronically denervated slow and fast muscles of rat

A study was conducted with chronically denervated adult female Wistar rats to test the hypothesis that synergistic tenotomy of denervated skeletal muscles does not just retard atrophy but produces an increase in muscle weight. The animals were categorized in three groups-denervated exercised (DE), denervated tenotomized (DT), and denervated-tenotomized-exercised (DTE). Mechanical stretch was induced in the DE group by forcing the animals to stand on their hind legs to reach for food and water. In the DT group, mechanical stretch was induced by tenotomy of two synergists in the gastrocnemius-plantaris-soleus complex of each leg of the rat so that either the soleus or the plantaris was left as the only plantar-flexor of the ankle joint in each leg. Mechanical stretch was induced in the DTE group by forcing the animals to stand after the tenotomy of synergists at eight weeks postdenervation. All animals in the three experimental groups, and in the sedentary control group (D) were sacrificed at nine weeks postdenervation; the soleus and plantaris muscles were removed and evaluated for MW, DW and percent of hydration. The slow muscle (soleus) increased in muscle mass in DT (53%), DE (26%), and DTE (17%). The fast muscle (plantaris) increased in weight in DE (18%) and in DTE (24%), but showed no significant changes in DT. Study results confirm the hypothesis that synergistic tenotomy stimulates an increase in muscle weight rather than merely retarding atrophy, and that this phenomenon can take place in the absence of neuronal influences. It is suggested that the increase in denervated muscle mass stimulated by muscle elongation is not a true work hypertrophy associated with significant changes in protein concentrations but only an adaptation to a new muscle length. The purpose of the adaptational changes is to optimize the overlap of actomyosin bridges in anticipation of forceful muscle contraction.