Abstract
Histochemical examination of rabbit, rat, guinea pig and mouse limb skeletal muscles in our laboratory has revealed that most red muscle fibers in any given muscle stain more intensely for glycogen (periodic acid-Schiff's reaction) than white or intermediate fibers. Since most studies have concluded that white muscle has more glycogen than red muscle, this discrepancy was investigated. Eleven vastus lateralis muscles were resected from six adult male guinea pigs and cropped to yield "red," "moderate" and "white" regions. Cross-sections of each region were employed for histochemical fiber typing and the remaining pieces for biochemical glycogen analysis. These analyses have shown the red region to have significantly more glycogen (9.7 mg per g) and more red fibers (77%) than the white region (7.4 mg/g, 29%). Having essentially eliminated intermediate fibers by cropping, these findings reflect glycogen concentration in red and white muscle fibers. The existence of significant numbers of intermediate fibers usually found in red muscles may be responsible for the frequently exhibited higher glycogen content in white muscles.