Contractile properties of muscle undergoing "compensatory" hypertrophy and its increased susceptibility to denervation and reflex atrophy.

Abstract

The contraction properties of the soleus muscle undergoing “compensatory” hypertrophy were studiedin situ in 120–150 g male rats 7 and 85 days after tenotomy of synergistic muscles. The time to peak of isometric twitch contractions in seven-day hypertrophy is somewhat prolonged, while the twitch tension is diminished as compared with control muscles of rats of corresponding weight and age. Maximum twitch tension of muscles hypertrophied by 26% is significantly reduced by 29% when calculated per gram dry muscle weight. Tetanic tension, on the other hand, was 13% higher in the hypertrophied muscles, but still lower when calculated per gram dry muscle weight. Eighty-five days after tenotomy of synergists, when there is still 15% hypertrophy of the soleus, there was a tendency of the various contraction paramaters to become normalized. The newly formed muscle mass during “compensatory” muscle hypertrophy is highly susceptible to the catabolic effects of denervation, or nociceptive stimulation. Superimposition of denervation or reflex atrophy (induced by fracture of metatarsal bones of the paw and turpentine oil injection) upon three-day hypertrophy led to a dramatic loss of weight. After four-day denervation, the soleus lost 42.7% in weight, the plantaris 28.0% and the extensor digitorum longus 24.4%. The corresponding values in the case of reflex atrophy were 26.5%, 25.5% and 17.7% respectively.