IGF-I binding and IGF-I expression in regenerating muscle of normal and hypophysectomized rats

Binding of iodinated IGF-I to tissue sections from regenerating muscle was studied by autoradiography in normal and in hypophysectomized rats. Binding of IGF-I was low in control muscle in both groups of animals, but increased transiently about 10-fold during regeneration after injury. Maximal binding occurred later in hypophysectomized rats than in control rats, and there was also a slower regeneration process in these animals. IGF-I, as demonstrated by immunohistochemistry, and IGF-I mRNA, as demonstrated by in situ hybridization, were expressed by the regenerating muscle cells in both groups of animals. It is concluded that locally produced IGF-I is the most likely ligand for IGF-I receptors during muscle regeneration.