Cultures of GH3 cells contain both single and dual hormone secretors.

Analysis of GH3 cultures by fixed sequential plaque assays revealed the presence of cells that release GH only, as well as those that release both GH and PRL (mammosomatotropes). Chronic treatment of these cultures with 17 beta-estradiol and TRH (factors found to alter the amounts of GH and PRL secreted) caused shifts in the overall proportions of GH to PRL secreting cells. Each agent, however, influenced the cultures differently. Estradiol treatment resulted in cultures which contained only mammosomatotropes, whereas TRH treatment resulted in cultures that contained PRL-only cells in addition to the other two functional cell types present in control populations. These results indicate that factors which alter the amounts of GH and PRL secreted by GH3 cultures also change the types of secretors present. Moreover, the manner in which the proportions of dual hormone secretors changed in response to these factors supports the view that multipotential cells serve as a transitional cell type in a conversion from GH to PRL secretors.