Structural characterization and immunohistochemical localization of receptors for insulin-like growth factor II in the rat pituitary gland

Insulin-like growth factor N (IGF-II) receptors were detected, localized, and structurally characterized in rat pituitary tissue sections and cultures of dispersed pituitary cells by immurtohistochemtstry, and affinity labeling with pel electrophoresis. Using highly specific antisera against IGF-II receptors (type 2 IGF receptors) and somatotropin (GH), intense type 2 receptor immunoreactivity was detected in both anterior and intermediate pituitary lobes. In anterior pituitary sections and cultures, type 2 receptor immunoreactivity colocalized to most GH-immunoreactive cells (somatc-tropes), as well as cells which did not contain GH. Intermediate lobe immunoreactivity was uniformly distributed throughout the parenchyma. In both anterior and intermediate pituitary lobes, type 2 receptor immunoreactivity was predominately localized to the plasma membrane of labeled cells, with little or no cytoplasmic labeling. GH immunoreactivity, on the other hand, was intracellular. Affinity labeling of microsomal membranes from anterior and neurointermediate pituitary tissues with '-M-IGF-II disclosed classical 230k type 2 receptors. The magnitude ofaffinity cross-linking from both lobes was similar to that of rat liver, indicating pituitary tissues, like liver tissue, are rich sources of type 2 receptors. These results suggest possible roles for IGF-II and the type 2 receptor in the regulation of synthesis or secretion of pituitary trophic hormones, including GH and proopiomelanocortin gene products.