Metabolism of red and white muscle fiber groups

Rat adductor fiber groups, predominantly composed of either red or white muscle fibers, have been utilized to demonstrate metabolic differences in these two types of voluntary skeletal muscle. Glycogen concentrations of muscle obtained immediately after sacrificing the rats were higher in white than in red muscle, but at the end of 2-hr incubation this relationship was reversed. No difference could be demonstrated in glucose uptake in the two types of muscle, while lactate production was greater in white than in red muscle. Acetoacetic acid uptake by red muscle was higher than that by white muscle as measured by chemical analysis and uptake of acetoacetic acid-C 14 . A lower percentage of acetoacetic acid-C 14 uptake appeared in the lactate fraction in white as compared to red muscle fiber groups. In the case of glycogen, this relationship was reversed and a larger percentage of C 14 uptake appeared in the glycogen fraction of white as compared to red muscle. Oxygen uptake and the counts from acetoacetic acid-C 14 appearing in C 14 O 2 were higher in red than in white muscle. The creatine phosphate level, after 2-hr incubation, was higher in white muscle. These data demonstrate striking differences in the relative distribution of various metabolic pathways in red and white muscle.