The influence of chronic dietary intervention on protein turnover and growth of the diaphragm and extensor digitorum longus muscles of the rat.

Changes in weight, protein, RNA and DNA contents of the E.D.L. and diaphragm muscles were studied in conjunction with aging and chronic dietary restriction. Between weaning and senescence both muscles exhibited progressive decreases in their fractional rates of growth, protein synthesis and protein breakdown; these rates being age for age higher in the diaphragm. Dietary restriction (50% of ad libitum food intake) from weaning onwards retarded muscle growth, particularly at the early stages (i.e. 4 weeks) after its implementation. Here the suppression of protein synthesis was due to the combined effects of piece meal feeding and long term reductions in food intake. Later, muscle sizes and total, but not fractional, synthetic rates were consistently decreased by chronic dietary intervention. The onset of the ageing atrophy may also be delayed by underfeeding. The changes in these 2 muscles have been compared to those in the whole animal and other striated muscles, as previously reported by the authors.