HISTOCHEMICAL AND MECHANICAL-PROPERTIES OF DIAPHRAGM MUSCLE IN MORBIDLY OBESE ZUCKER RATS

The purpose of the present study was to evaluate the effects of chroni c mass loading produced by obesity on the structural and functional ch aracteristics of the diaphragm in lean and obese Zucker rats. The trap ezius muscle served as an internal control. The studies were carried o ut on 17 lean (303 +/- 24 g) and 16 obese (698 +/- 79 g) Zucker rats. We observed that the diaphragms from obese animals were restructured s uch that the overall contribution of type I and IIa fibers was signifi cantly increased. As a consequence of this remodeling, overall diaphra gm thickness was selectively greater in obese animals. In small isolat ed diaphragm bundles studied in vitro, we also detected a reduction in specific force in obese animals that was not detected in the trapeziu s muscle. In vitro fatigue resistance, assessed by repeated stimulatio n, was similar in muscles of lean and obese animals. Diaphragm fiber o xidative capacity (succinate dehydrogenase activity) was also comparab le in lean and obese animals. We conclude that in obesity the diaphrag m undergoes modest remodeling that may be beneficial in enhancing forc e generation.