Alterations in enzyme histochemical characteristics of the masseter muscle caused by long-term soft diet in growing rabbits.
OBJECTIVE
Recently young people have an increasing tendency to intake an easily chewable diet and spend less time on mastication. The aim of the present study was to investigate the histochemical effects of long-term soft diet on the masseter muscle in growing rabbits.


METHODS
Twelve young male Japanese white rabbits were divided into two groups (n = 6 each) at weaning (1 month after birth) and fed a solid diet (control group) or a powder diet (soft-diet group). The duration of the experimental period was 6 months. Masseter fibers from the superficial and the deep portions were histochemically defined as type 1, 2A, 2B, or 2C fibers.


RESULTS
As compared with that of the control, the deep masseter of the soft-diet group showed a significantly lower ratio of type 1 fiber cross-sectional area to total area (6.3 and 10.1% for the soft-diet and control group, respectively), significantly more type 2A fibers (74.0%vs 50.3%) and significantly fewer type 2B fibers (4.3%vs 12.5%). However, fiber size did not differ between the two groups. NADH-tetrazolium-reductase (NADH-TR) of the masseter was less reactive in the soft-diet group, reflecting a lower oxidative capacity.


CONCLUSIONS
These findings indicate that the alteration of the functional activities contributed to selective disuse influences on the type 1 and type 2B fibers, and a resultant increase in type 2A fibers. This study suggests that long-term alteration of jaw function induced by a soft diet can lead to adaptations of the masseter muscle.
Division of Dentistry and Oral Surgery, Department of Sensory and Locomotor Medicine, University of Fukui, Matsuoka, Fukui, Japan. ykitagaw@fmsrsa.fukui-med.ac.jp
Y
Y
Kitagawa
K
K
Mitera
T
T
Ogasawara
Y
Y
Nojyo
K
K
Miyauchi
K
K
Sano
D000222:Adaptation, Physiological / Q000502:physiology; D000251:Adenosine Triphosphatases / Q000032:analysis; D000818:Animals; D004032:Diet / Q000145:classification; D005502:Food; D008297:Male; D008406:Masseter Muscle / Q000201:enzymology* / Q000254:growth & development / Q000648:ultrastructure; D018656:Muscle Fibers, Fast-Twitch / Q000201:enzymology / Q000648:ultrastructure; D018657:Muscle Fibers, Slow-Twitch / Q000201:enzymology / Q000648:ultrastructure; D009246:NADH Tetrazolium Reductase / Q000032:analysis; D010084:Oxidation-Reduction; D011817:Rabbits; D011897:Random Allocation; D013997:Time Factors
D009246:NADH Tetrazolium Reductase; D000251:Adenosine Triphosphatases