IGF-I, bFGF AND TGF-?? IMMUNOREACTIVITIES AFTER ECCENTRIC CONTRACTION-INDUCED MUSCLE INJURY IN VIVO

Abstract

584 Many in vitro studies have suggested that local growth factors play important roles for skeletal muscle regeneration. It has not been clearly shown that when and where these growth factors express in muscle tissue during regeneration process after exercise-induced muscle injury. This study immunohistochemically examined the time course of changes in insulin-like growth factor (IGF-I), basic fibroblast growth factor (bFGF), and transforming growth factor beta (TGF-β) immunoreactivities after eccentric contraction-induced muscle injury in vivo. Immunoreactivities of the growth factors in the tibialis anterior (TA) muscle of adult female Wistar rats (6-8 months) were compared between the right and left limb on 6 successive days(3-4 rats /group, n=20) after eccentric contractions. The right TA was subjected to a bout of 50 eccentric contractions elicited by electrical stimulation, and the left TA was served as a noncontraction control. The IGF-I immunoreactivity started to increase at 1 day after contractions and the most pronounced increase was observed at 4 days within the cytosol and the mononuclear cells of the extra cellular space of damaged fibers. The level gradually decreased to the control level thereafter. The bFGF level only elevated at 4-5 days particularly at the mononuclear cells in the extra cellular space. The level of TGF-β slightly increased at 1 day, and markedly increased at 3 days around the mononuclear cells, then gradually decreased by 4-6 days. It is concluded that the level and the time course of changes in immunoreactivities were different among IGF-I, bFGF, and TGF-β during regeneration after eccentric contraction-induced muscle injury. The mononuclear cells around the damaged fibers were intensely stained for all of the growth factors.