Immunohistochemical detection of components of the insulin-like growth factor system during skeletal muscle growth in the pig

The insulin-like growth factor (IGF) system plays an important role in post natal somatic and skeletal muscle growth in pigs. There is little informati on on the occurrence and distribution of components of the IGF system in po stnatal porcine skeletal muscle. IGF-I, IGF receptor 1 (IGF1R) and the IGF- binding proteins IGFBP-1 and -3 in longissimus dorsi and triceps brachii we re localized in muscle biopsies from 12 commercially crossbred pigs aged fr om 28 to 199 days as well as from the sire generation, by immunohistochemis try. Plasma IGF-I concentrations were also determined using radioimmunoassa ys. Unlike other species, IGF-I was localized in porcine skeletal muscle fi bres. Staining intensity correlated with the highest plasma IGF-I levels an d phases of intensive muscle growth from the 11th to 22nd week. The pattern of IGF1R immunostaining, which was strong, correlated with that of IGF-I. IGF1R was also localized in endomysial tissues. IGFBP-1 was not detected wi thin muscle fibres, but was found in the endomysium and vessel walls, while IGFBP-3 was localized with IGF-1 and its receptor. Higher magnification re vealed that IGF1R, IGFBP-3 and probably IGF-I appeared in the tubular syste m. Inhibitory as well as stimulating controls of IGFBP-1 and -3 on IGF func tions are discussed, which may maintain a balance between autocrine growth promoting activities of IGF-I and IGF1R.