Effects of soft diet on rat masseter muscle mitochondrial development.

There is not fine information regarding the influence of diet on development of masseter muscle and its mitochondria. Objective of this study is to compare mitochondrial enzyme activity, and morphology of masseter muscle fiber cells and its mitochondria prepared from rats fed soft diet to those fed hard diet. Cross-sectional area of fiber cells and number of mitochondria per unit area prepared from rats fed hard diet were greater than those of animals fed soft diet on postnatal day 60, and these differences decreased under both feeding conditions on days 120. Structure of mitochondrial cristae of rat fed hard diet was clear but that of fed soft diet ambiguous and contains many halos. Mitochondrial succinate-O2 and NADH-O2 oxidoreductase activities isolated from rats fed hard diet were higher than those of soft diet group over the period from days 30, and differences in both diet groups became the largest on days 60, and decreased on days 120. Our results indicated that development of masseter muscle fiber cells and mitochondria is hindered when rats are fed soft diet, but recover partially later, and hard diet is required for normal development of masseter muscle.