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 muscles after tenotomy, muscle fibres degenerated and some of them were destroyed; the muscle did not seem to recover until the 35th day. On the 14th day, some small muscle fibres, probably regenerating muscle fibres, started forming within the basal-lamina tube and remained after necrosis of a pre-existing muscle fibre. Most capillaries at each stage were of the continuous type. However, about 10% of the capillaries around degenerated muscle fibres at days 4, 7 and 14 consisted of endothelial cells with a small number of fenestrae bridged by a single-layered diaphragm. On the 14th day, capillaries around small regenerating muscle fibres also often had a small number of fenestrations. Even on the 35th day, capillaries occasionally had fenestrations. Additionally, some of the fenestrated capillaries formed small pores at the fenestrated portion of the endothelial cells. The untreated muscles contained only continuous capillaries. These findings suggest that fenestrations in the endothelial cells may occur in intramuscular capillaries not only around degenerated muscle fibres but also around regenerating muscle fibres after tenotomy.