[Metabolic mechanisms of different types of disuse muscular atrophy]

Radiotracer studies in vivo on protein biosynthesis have been made in red (m. soleus) and white (m. extensor digitorum longus) rat shin muscles during their disuse atrophy caused by foot exarticulation. The rate of protein biosynthesis (as calculated per mass unit of total RNA) was increased in the white muscle on the 4th and 14th days, being unaltered on the 7th day after the surgery, but this rate was decreased in the red muscle at all these stages. The data obtained suggest that all these stages. The data obtained suggest that the atrophy, more pronounced in the red muscle than in the white one, can be mainly attributed in the former to decreased protein biosynthesis but in the latter to the increased protein degradation.