CAGE-SIZE, GENDER AND MEASUREMENT ISSUES IN THE STUDY OF MUSCLE FATIGABILITY (HISTOCHEMISTRY).
AuthorRankin, Lucinda Lee
AdvisorStuart, Douglas G.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractTo study the detrimental effects of hypokinesia, many models of reduced muscular activity (i.e., reduced-use), including alterations in the size of the living environment, have been developed. Although significant structural and functional changes have been documented, the effect of reduced-use on muscle fatigability remains unclear. This project was designed to study the effects of cage-size on selected properties of rat hindlimb muscle, with particular emphasis on fatigue. Further, in view of the lack of information on the potential effect of gender, both males and females were studied. The rats were raised in either a small, conventional cage or one approximately 133 times larger. Subsequently, terminal experiments were performed to characterize the contractile properties, fiber-type composition and oxidative potential of two hindlimb muscles of the small- and large-cage-reared rats. The test muscles, soleus and extensor digitorum longus, were selected on the basis of their pronounced differences in function, usage and fiber-type composition. The results suggest that reductions in cage-size can influence the properties of skeletal muscle (specifically, muscle mass, force and fatigability) and that this effect is a function of both gender and interanimal differences. However, due to the large variability exhibited by all three factors, their overall effect will be minimal. An analysis of the response of the test muscles to a 6 min fatigue test revealed three findings. First, both muscles exhibited a wide range of fatigability, an unexpected finding particularly for soleus but in keeping with the multiplicity of factors discussed above. Second, the association observed between whole-muscle force and the electromyogram (e.m.g.) was found to be dependent upon the measure used to quantify the e.m.g., the fiber-type composition of the muscle and its degree of fatigability. And third, a coexistence of twitch potentiation and muscle fatigue was observed which also was dependent upon the fiber-type composition and the extent of fatigue. Finally, a comparison of qualitative and quantitative histochemical analyses revealed broad, overlapping ranges for oxidative enzyme activity for each of the three muscle-fiber types. This suggests that differences in fatigability usually attributed to different fiber types are not due solely to differences in oxidative potential.