Novel clonal strains from adult rat anterior pituitary producing S-100 protein.

S-100 protein, one of the unique proteins found in the nervous system, has recently been discovered unexpectedly in the rat anterior pituitary. Immunocytochemistry reveals that stellate, follicular and folliculostellate cells, and marginal cells of the rat anterior pituitary contain this protein; however, as far as we know, there are no reports on the physiological role of this protein in the anterior pituitary. In the study reported here, three S-100 protein-producing clonal strains (JH-S3, JH-S8 and JH-S12) from adult rat anterior pituitaries were established by using the single cell-plating feeder layer method. These new clonal strains reveal that the S-100 protein-producing cell is an independent cell type of the anterior pituitary. Both cultures and grafts of the JH-S3 cells stain immunocytochemically with anti-S100 protein IgG fraction. Moreover, the S-100 protein and conditioned medium of JH-S3 clonal cells both stimulate release of prolactin from prolactin-secreting clonal cells (1G4) in vitro.