Effect of age on the response of four muscles of the rat to denervation

Abstract

Gastrocnemius, plantaris, soleus, and hemidiaphragm muscles were denervated in rats from birth to old age. Change from the initial weight of each muscle was determined and compared with extent of difference from theoretical normal weight. An increase over initial weight occurred in denervated hemidiaphragms of all ages. Duration and extent of increase were greatest in young animals. Denervated leg muscles of newborn animals continued to grow to 56 days. With increasing age this ability was gradually lost and from body weights of 200 g to 500 g the rates of loss of weight were similar. The response expressed as percent difference from theoretical normal weight depends on the balance between growth rate of normal muscle and degree to which the denervated muscle retains a net synthetic ability. The latter seems to be related to the extent of stretch of the denervated muscle caused by skeletal elongation. Supporting this is the observation that tenotomy enhances atrophy due to denervation only when limb bones are rapidly elongating.