Characterization of insulin-like growth factor II peptides secreted by explants of neonatal brain and of adult pituitary from rats.

This study compares the molecular characteristics of the insulin-like growth factor II (IGF-II) peptides synthesized and secreted by explants of neonatal brain and adult pituitary of rat to those produced by the Buffalo rat liver cell line (BRL-3A). Metabolic labeling, followed by immunoprecipitation and sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that the rat brain and liver cells synthesized and secreted the following immunoreactive IGF-II peptides: 19, 11, 10, and 8.7 kilodaltons (kd), whereas the rat pituitary secreted the 10 and 8.7 kd peptides. However, the brain and pituitary explants failed to secrete the mature 7.5 kd IGF-II peptide which was a major species secreted by the liver cells. In the brain and pituitary, the predominant form of IGF-II peptide secreted was the 8.7 kd. This result suggests that 1) different mechanisms of processing of the IGF-II precursor and/or the preferential translation of different messenger RNA (mRNA) species may exist in different cell types, and 2) the 8.7 kd IGF-II peptide may be the biologically relevant molecule in the central nervous system of the rat.