Fibroblast growth factor is stored in fiber extracellular matrix and plays a role in regulating muscle hypertrophy.

A polyclonal antibody specific to bovine basic fibroblast growth factor (bFGF) localizes bFGF in the extracellular matrix of rat skeletal muscle fibers, where it is bound by the heparin-rich basal lamina. FGF accumulation appears to be augmented in hypertrophied compared to control fibers. In addition, FGF-like growth activity can be isolated from hypertrophied muscle. This growth activity binds to heparin and can be purified by heparin-affinity chromatography. When assayed in a chick myogenic cell culture system, the purified rat growth activity stimulates myobenic cell replication and stimulates myosin accumulation and synthesis. The function, in vivo, of basal lamina-localized FGF in rat muscle is not known, but it is most probably related to increased satellite cell replication seen during normal fiber maturation, during work-induced hypertrophy, and during regeneration. During hypertrophy, we observe the appearance of new fibers in addition to growth of preexisting fibers. It is hypothesized that muscle hypertrophy involves activation of satellite cells which may then fuse with existing fibers and, in addition, also form new fibers.