Differential effects of insulin‐like growth factor‐I on matrix and DNA synthesis in various regions and types of rabbit tendons

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Abstract
Tendon healing and integration of tendon grafts may be site or donor specific. To determine if differences exist in sensitivity to growth factors that have the potential to influence tendon repair, we compared the effects of recombinant human insulin-like growth factor-I on various types of tendon segments. The dose response effects on proteoglycan, collagen, noncollagen protein, and DNA synthesis were investigated in short-term explant cultures of intrasynovial intermediate and proximal segments of deep flexor tendons, extrasynovial segments of deep flexor tendons, and Achilles tendons of rabbits. The four different types of tendon segments cultured in media without recombinant human insulin-like growth factor-I synthesized similar amounts of each of the matrix components. Intrasynovial proximal segments synthesized 15 times less DNA than other tendon segments. Recombinant human insulin-like growth factor-I stimulated matrix and DNA synthesis of all tendon segments in a dose-dependent manner in intervals from 10 to 1,000 ng/ml. The potency (LogED50) of the stimulation did not differ between the segments. The estimated maximal stimulation (Emax) of proteoglycan synthesis by recombinant human insulin-like growth factor-I was higher, and of collagen and noncollagen protein synthesis was lower, in intrasynovial proximal segments as compared with that of the other types of segments. In contrast, the estimated maximal stimulation of DNA synthesis by recombinant human insulin-like growth factor-I was 6-fold higher than controls in all types of tendons. These findings demonstrate differences in mitotic capacity between anatomical regions of tendons during culture without recombinant human insulin-like growth factor-I and in matrix synthesis after stimulation with it.