INSULIN-LIKE GROWTH-FACTOR-I (IGF-I) AND IGF-BINDING PROTEINS IN RAT WOUND FLUID

Insulin-like growth factors (IGFs) play an important role in tissue re pair, including healing of dermal and epidermal injury. In this study we have measured changes in the IGF:IGF-binding protein (IGFBP) profil e of rat wound fluid (WF) collected after sc implantation of Hunt-Schi lling chambers for 21 days. WF IGF-I levels 1 day after implantation w ere equivalent to plasma levels, then fell during the first 7 days bef ore recovering to approximately two thirds of plasma levels by day 21. Western ligand blots of whole WF revealed a profile qualitatively sim ilar to that found in plasma, although the intensity of the IGFBP-3 ba nd was significantly less than that in plasma. Neutral gel chromatogra phy of pooled day 14 WF, after in vitro incubation with [I-125]IGF-I, Separated the radioligand into three distinct regions of 150, 40, and 7.5 kDa. However, compared to plasma, recovery of[I-125]IGF-I in the 1 50-kDa region in WF was reduced, and that in the 40-kDa region was inc reased. Ligand blotting of the WF-derived neutral gel fractions reveal ed IGFBP-3 within the 150-kDa complex. Incubation of WF with plasma (1 :1, vol/vol) resulted in a progressive decline in the intensity of the plasma IGFBP-3 band. Protease inhibitors, including EDTA, antipain, o r aprotonin, inhibited this process. We have described the changes ove r time in WF IGF-I concentrations, characterized the IGFBP profile, an d demonstrated the presence of IGFBP-3 proteolytic activity in WF. The latter may play a role in the regulation of IGF bioavailability durin g the repair process.