Abstract
The fiber type composition and capillary supply in the rat diaphragm were compared with those of different hindlimb muscles. And then, the effects of sex difference and growth on these characteristics of the diaphragm were studied. Muscle samples obtained from the anesthetized rat were rapidly frozen and sliced transversely in a cryostat. The sections were stained histochemically by the succinate dehydrogenase method and the myosin adenosine tri-phosphatase method after preincubation at pH 4.3 to typify fibers. The capillaries were stained by the myosin adenosine triphosphatase method after preincubation at pH 4.0. The following results were obtained. The greater part of the rat diaphragm was composed of fast twitch fibers, as well as the fast muscle. The capillary supply in the diaphragm was richer than that of the hindlimb muscles studied. For the fiber type composition, there were no differences between male and female rats. The muscle capillarity in the female rats were more richer than that of male rat. The growth causes the changing properties of the motoneurons and the new capillary formation in the diaphragm. Since the diphragm was already adapted to a highly repetitive and low resistance type of activity, it assumed that the histochemical and morphological characteristics of the muscle fibers were related to the functional requirements of the diaphragm.
