Presence of IGF-1-like peptides in the neuroendocrine system of the Atlantic hagfish, Myxine glutinosa (Cyclostomata): evidence derived by chromatography, radioimmunoassay and immunohistochemistry

By the use of radioimmunoassay and chromatography peptides related to insulin-like growth factor 1 (IGF-1) have been identified in the cylostomian species Myxine glutinosa. IGF-1-like-immunoreactivity was detected in serum as well as in brain, intestine, pancreas and liver. After acid gel chromatography, the IGF-1-like immunoreactivity eluted as one major peak, with an apparent molecular weight of between 2-4 kDa. When the same antiserum was applied immunohistochemically, IGF-1-like-immunoreactivity was observed in endocrine cells of the mucosal epithelium throughout the primitive intestinal tube. These cells were of the open type and occurred in small clusters. In addition, the majority of the endocrine cells of the pancreas of Myxine displayed IGF-1-like-immunoreactivity. In some of the specimens investigated IGF-1-like-immunoreactive perikarya and fibers were observed on all levels of the brain. Distribution patterns and densities of the IGF-1-like-immunoreactive structures in Myxine correlated with the measurements obtained by radioimmunoassay. Absorption studies with insulin- and IGF-related peptides as well as with crude extracts and the peak material obtained after gel chromatography indicated that the IGF-1-like peptides in Myxine are different from mammalian and non-mammalian insulins as well as from mammalian IGF-1. Generally, the results suggest a long phylogenetic history of IGF-1-like peptides and indicate their fundamental functional impact in all vertebrates.