Somatomedin C immunoreactivity in the Achilles tendon varies in a dynamic manner with the mechanical load

Publisher Website
Google Scholar
Abstract
Distribution of the trophic peptide somatomedin C (Sm‐C; insulin‐like growth factor I; IGF‐I) immunoreactivity was mapped in normal Achilles and tibialis anterior tendons. The spindle‐shaped tendon fibroblasts showed faint perinuclear staining. Fibroblasts in the paratenon mostly had a more intense IGF‐I immunoreactivity, i.e. faint to moderate. When analysing either tendon in detail, areas with more intense IGF‐I immunoreactivity could be recognized and seemed to correlate with areas of high mechanical stress. Increased mechanical load induced over 3 days elevated IGF‐I immunoreactivity throughout the cytoplasm of tendon fibroblasts. Peak intensity was reached in 7 days, and thereafter the IGF‐I immunoreactivity seemed to decrease irrespective of persistent high mechanical load. Training the animals on a treadmill for from 20 up to 60 min per day for 5 days induced after 3–5 days increased IGF‐I immunoreactivity throughout the cytoplasm of the tendon and paratenon fibroblasts. Sudden curtailment of loading the Achilles tendon resulted in a marked reduction of the IGF‐I immunoreactivity in most fibroblasts within 3 days. After a week only a small number of tendon fibroblasts showed any IGF‐I immunoreactivity. The IGF‐I immunoreactivity of tendon fibroblasts thus correlates to mechanical loading of the tendon. It is proposed that IGF‐I may have a trophic influence on tendon and paratenon cells by autocrine and/or paracrine mechanisms.