Matrix metabolism and healing in the flexor tendon. Experimental studies on rabbit tendon.

I. The rabbit flexor tendon within the synovial sheath contains segments with fibrocartilage-like areas. These segments have a higher proteoglycan and a lower collagen and non-collagen protein synthesis compared to the segment with "true" tendon tissue. Cell proliferation is also lower within the proximal segment than in the intermediate and distal segments. These regional variations should be considered when interpreting experimental data. They may also be of importance for the variable healing capacity of different flexor tendon regions. II. Recombinant human insulin-like growth factor, insulin and fetal calf serum stimulate matrix synthesis and cell proliferation in a dose dependent manner in flexor tendon explants cultured for three days. rhIGF-I was more potent than insulin in stimulating cell proliferation and matrix synthesis. rhIGF-I also stimulated matrix synthesis to a higher degree than FCS. III. In long-term culture of flexor tendon explants, the addition of rhIGF-I to the culture medium stimulates matrix synthesis, but does not influence turn-over rates. The total hexosamine and collagen contents in tendons cultured in medium with rhIGF-I remain at the same level, while non-collagen protein content decreases. There are no major differences in matrix metabolism between tendons cultured in medium supplemented with FCS or with rhIGF-I only. rhIGF-I may therefore be used as a growth factor supplement in serum-free culture of tendon tissue. IV. Dehydration inhibits in vitro matrix synthesis and cell proliferation in tendon explants. These effects are counteracted by keeping the exposed tendon segments moist with physiological saline solution during preparation. The sensitivity of tendon tissue to dehydration should be considered during tendon surgery. V. Tendon explants, cultured in a diffusion chamber, survive and exhibit an intrinsic capacity for healing. In healing tendon segments incubated for three weeks, protein synthesis remains unchanged and collagen synthesis decreases, whereas the rate of cell proliferation increases as compared with native tendons. VI. Endotenon cells of the rabbit flexor tendon can restore the injured tendon surface and bridge the tendon gap. The rabbit flexor tendon is a morphologically and biochemically heterogeneous tissue with an intrinsic capability for healing. Tendon tissue is susceptible to dehydration and during exposure quickly looses its viability. The metabolic and proliferative capacity of the tendon is stimulated by growth factors and rhIGF-I may be of importance in tendon healing.