Effect of ageing on ultrastructure of slow and fast skeletal muscle tendon in rabbit Achilles tendons.

This reports presents the changing morphological characteristics of collagen and fibroblasts in the soleus and gastrocnemius muscle tendon of female Japanese white rabbits with ageing. The fibroblasts decreased in number per 37 microns 2 with ageing in each group, and their morphology became longer and more slender through ageing. The mean fibril area and diameter of the collagen fibrils of soleus muscle tendon (SMT) and lateral gastrocnemius muscle tendon (GMT) in 8- to 10-month old rabbits were significantly higher than those of 3-wk-old rabbits during growth (P < 0.01). The mean area and diameter of collagen fibrils of SMT and GMT decreased during senescence: the values for 4- to 5-yr-old rabbits were lower than those for 8- to 10-month-old rabbits, but the difference was not significant. Statistically significant differences in fibril area and diameter between the SMT and GMT were not found during ageing. The number of thick fibrils increased during growth, but decreased in senescence. There were more thin fibrils (30-60 nm) in the 3-wk-old rabbits than in the 8- to 10-month old and 4 to 5-yr-old groups, and the large-diameter collagen (300-360 nm) was more abundant in the 8- to 10-month-old group than in the 3-wk-old and 4- to 5-yr-old groups. Differences in fibril size between slow and fast muscle tendons were not observed during ageing.