Characterization of Insulinlike Growth Factor I Produced by Fetal Rat Pancreatic Islets

Pancreatic islets were prepared from 22-day-old rat fetuses. After 5 days of culture in dishes allowing cell attachment, neoformed islets were kept free floating in RPMI-1640 medium (16.5 mM glucose, 1% fetal calf serum). The islets were then pulsed with [³H]leucine and [³⁵S]methionine for 24 h. The conditioned medium was acidified with acetic acid (final pH 2.7), desalted, concentrated, and gel filtered on Bio-Gel P100 in acid conditions. The radioactive material that comigrated with immunoreactive insulinlike growth factor I (IGF-I) produced by the islets was pooled, concentrated, and further characterized by reverse-phase high-performance liquid chromatography on a C₁₈Bondapak column with a linear gradient of acetonitrile (20–80%). The radioactive material that eluted as pure IGF-I (40% acetonitrile) was further studied by chromatofocusing on a Pharmacia PBE 94 column. A sharp radioactive peak containing [³H]leucine and [³⁵S]methionine was eluted at pH 8.55. This material was immunoprecipitated with an antiserum to IGF-I. This study demonstrated that fetal islet cells synthesize molecules that are, by several criteria, equivalent to native IGF-I.