Characteristics of compensatory hypertrophied muscle in the rat: I. Electron microscopic and immunohistochemical studies.
BACKGROUND
Complex branched muscle fibers are frequently observed in the muscles of mdx mutant mice and/or in damaged muscles. To investigate whether the complex branched fibers were present in the compensatory hypertrophied muscles of rats, we examined the morphological changes in these muscles.


METHODS
We examined the hypertrophied plantaris (PLA) muscle of the Wistar male rats, prepared by surgical ablation of synergistic muscles. The muscle was examined using three-dimensional analysis with scanning electron microscopy, immunohistochemical detection of proliferating cells using 5-bromo-2'-deoxyuridine (BrdU) and histological and histochemical characterization. Studies were performed at 48 hours, 2, 4, 6, 10, and 15 weeks after surgical preparation.


RESULTS
The muscle hypertrophy ratio (muscle weight relative to the contralateral intact control side), gradually increased from 2 to 10 weeks, and the peak value (48.6%) occurred at the 10th week. The total number of fibers did not change significantly at any time interval. However, the number of branched muscle fibers increased significantly (P < 0.05) after 6 weeks, and accounted for about 2.5% of the total fibers at the 15th week. Most branched fibers showed complex features resembling the "anastomosing syncytial reticulum" described in myopathic animals. The fibers were observed mainly in the middle and distal portions of the PLA muscle. The proportion and distribution of proliferating cells in the entire PLA muscle corresponded with the distribution of the complex branched fibers. These results were also observed in muscle tissues prepared for histological and histochemical examination.


CONCLUSIONS
The presence of a large proportion of complex branched fibers in a limited segment of the compensatory hypertrophied muscle suggests that this hypertrophy model represents a pathological and/or pathophysiological hypertrophy model rather than a normal physiological process.
Tamaki
T
T
Department of Physiology, Tokai University School of Medicine, Kanagawa, Japan.
Akatsuka
A
A
Tokunaga
M
M
Uchiyama
S
S
Shiraishi
T
T
D000222:Adaptation, Physiological; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002455:Cell Division; D002802:Cholinesterases / Q000378:metabolism; D004247:DNA / Q000032:analysis; D006984:Hypertrophy / Q000473:pathology; D007150:Immunohistochemistry; D008297:Male; D008855:Microscopy, Electron, Scanning; D008954:Models, Biological; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000473:pathology / Q000648:ultrastructure*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000473:pathology / Q000502:physiology / Q000648:ultrastructure*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D004247:DNA; D002802:Cholinesterases; D000251:Adenosine Triphosphatases