Morphological changes of capillaries in the rat soleus muscle following experimental tenotomy

We examined the structural changes of capillaries in the rat soleus muscle 4, 7, 14, and 35 days after experimental limb tenotomy. In the soleus muscl es after tenotomy, muscle fibres degenerated and some of them were destroye d; the muscle did not seem to recover until the 35th day. On the 14th day, some small muscle fibres, probably regenerating muscle fibres, started form ing within the basal-lamina tube and remained after necrosis of a pre-exist ing muscle fibre. Most capillaries at each stage were of the continuous typ e. However, about 10% of the capillaries around degenerated muscle fibres a t days 4, 7 and 14 consisted of endothelial cells with a small number of fe nestrae bridged by a single-layered diaphragm. On the 14th day, capillaries around small regenerating muscle fibres also often had a small number of f enestrations. Even on the 35th day, capillaries occasionally had fenestrati ons. Additionally, some of the fenestrated capillaries formed small pores a t the fenestrated portion of the endothelial cells. The untreated muscles c ontained only continuous capillaries. These findings suggest that fenestrat ions in the endothelial cells may occur in intramuscular capillaries not on ly around degenerated muscle fibres but also around regenerating muscle fib res after tenotomy.