Abstract
To examine the muscle pathology of obstructive vascular disorders, ischemic muscles were produced experimentally by arterial clamping, and changes in the muscle spindles were observed histochemically. The subjects were 9 male cats for ischemic muscle pathology, and 4 normal controls. The abdominal aorta, right common iliac artery and right femoral artery were clamped simultaneously for 8 hours, and the animals were sacrificed 3 days after the surgery. The right anterior tibial muscles were then isolated immediately and each was divided into 4 blocks. Each block was frozen by liquid nitrogen, and serial transverse sections were made by cryostat. Muscle spindles in each segment through the central, equatorial to the peripheral polar regions were confirmed microscopically. Histochemical staining was then carried out using NADH-Tetrazolium reductase stain and myosin ATPase stain (pH 4.6) . Results: 1) Muscle spindles of normal control: The average numbers of muscle spindles in each block from the rostral to the caudal side in the anterior tibial muscles were 4.5, 4.8, 6.3, 3.5, respectively. Many muscle spindles were situated along the anterior tibial artery and beside the major branches of the artery. The average diameter of each muscle spindle in the equatorial region was 100-180 μm. Capsule thickness was 3-7 μm. Each intrafusal muscle fiber consisted of 2 bag fibers, and 4 to 6 chain fibers. Hypoactivity was evident in the equatorial region in both NADH-TR and ATPase (pH 4.6) histochemical staining. In the paraequatorial and polar regions, however, bag 1, bag 2 and chain fibers were clearly evident from the enzymatic activity of both NADH-TR and ATPase. Regional differences in ATPase staining (pH 4.6) occurred along the bag 1 fiber but not along the bag 2 and chain fibers. The microvasculature of the muscle spindle and its relations to the extrafusal muscle were also observed. Capillaries in muscle spindle were larger than those in extrafusal muscle. 2) Ischemic changes in muscle spindles: From comparison of changes in muscle spindles and extrafusal muscle, muscle spindles were well preserved histochemically in the group without any lesions at the extrafusal muscle. NADH-TR activity of type I fiber was selectively reduced in the group in which the extrafusal muscle was affected slightly, whereas NADH-TR activity of intrafusal muscle fibers was well preserved. Both NADH-TR and ATPase activities in intrafusal and extrafusal muscle fibers were reduced markedly in the group in which the extrafusal muscle was affected severely. No regional sensitivity of ischemic muscle spindles was observed histochemically. Conclusion : Ischemic changes of muscle spindle were clearly less than those of extrafusal muscle. Capillaries in muscle spindles that were larger than those in extrafusal muscle might be a factor in determining ischemic resistance of intrafusal muscle.
