Immunohistochemical localization of anterior pituitary hormones in S-100 protein-positive cells in the rat pituitary gland

In the anterior and intermediate lobes of the rat pituitary gland, non-hormone-producing cells that express S-100 protein coexist with various types of hormone-producing cells and are believed to function as phagocytes, supporting and paracrine-controlling cells of hormone-producing cells and stem cells, among other functions; however, their cytological characteristics are not yet fully understood. Using a transgenic rat that expresses green fluorescent protein under the promoter of the S100 beta protein gene, we immunohistochemically detected expression of the luteinizing hormone, thyroid-stimulating hormone, prolactin, growth hormone and proopiomelanocortin by S-100 protein-positive cells located between clusters of hormone-producing cells in the intermediate lobe. These findings lend support to the hypothesis that S-100 protein-positive cells are capable of differentiating into hormone-producing cells in the adult rat pituitary gland.