AbstractAffinity purified polyclonal antibodies directed against human recombinant acidic FGF (aFGF), were used in immunofluorescence studies to localize this growth factor in several normal and dystrophic (mdx) mouse skeletal muscles. The expression of aFGF was detected throughout the life of both the control and mdx mice. In striated muscles, examined up to 3 weeks postnatal, aFGF was localized around the myofibres and this pattern was consistent in both mdx and the normal counterpart strain. However, the intensity of the signal was much stronger in the mdx strain. In mdx mouse skeletal muscles, examined during the acute phase of degeneration and regeneration (3-14 weeks) aFGF was localized around the myofibres, in approximately 60% of the nuclei of newly formed or regenerated myofibres and also in the pockets of necrosis which represented actively degenerating myofibres. In normal mouse skeletal muscles, studied over the same period, the antibodies localized aFGF mainly to the periphery of the muscle fibres. The augmentation of aFGF observed by immunofluorescence in mdx mouse muscles was confirmed by enzyme immunoassay (EIA) analysis of the same muscles over the same period of time. The data from the EIA indicated a 3.5-fold increase in aFGF in mdx as compared to normal muscles at 3 weeks, and an approximate 26-fold increase during the period of active degeneration-regeneration. This increased concentration of aFGF noted in the mdx muscles suggests that this endogenous aFGF may participate in the high level of regenerative activity observed in mdx mouse.