In vitro production of IGF-binding proteins (IGFBP) by various organs of the striped bass, Morone saxatilis

Production in vitro of insulin-like growth factor-binding proteins (IGFBP) by various organs of the striped bass, Morone saxatilis, was examined by organ culture. Fifteen organs were removed, dissected into small pieces and incubated in Minimum Essential Medium (MEM) containing antibiotics. After 6 h of preincubation to remove blood contaminants, the medium was changed and incubation was continued for an additional 36 h. Media containing approximately 10 μg proteins from each organ were electrophoresed using a discontinuous polyacrylamide gel followed by Western ligand blotting with 125I-labelled human IGF-I as a probe. Striped bass (sb) IGFBP-1 was detected only in medium from liver. sbIGFBP-2 was always present in media from liver, pituitary, trunk kidney and bulbus arteriosus and was detected occasionally in media from optic lobe of the brain, ceratobranchial cartilage, ceratobranchial bone, heart, spleen, gonad and gut. Trace amounts of sbIGFBP-3 were detected in medium from liver. Other sbIGFBPs were not detected in striped bass using this system. Although striped bass IGFBPs may not directly correspond to mammalian IGFBPs of similar molecular weight, multi-organ IGFBP production appears to be an evolutionarily-conserved mechanism in vertebrates, evident in both teleosts and mammals.