Cultures of GH3 cells are functionally heterogeneous: thyrotropin-releasing hormone, estradiol and cortisol cause reciprocal shifts in the proportions of growth hormone and prolactin secretors.

Utilization of reverse hemolytic plaque assays revealed that cultures of GH3 cells are not functionally homogeneous, but contain approximately twice as many GH as PRL secretors. Chronic treatment of these cultures with TRH, estradiol, or cortisol (factors that induce reciprocal alterations in the amount of GH and PRL released by entire cultures of GH3 cells) caused reciprocal shifts in the proportions of GH and PRL cells, without influencing the combined percentages of hormone-secreting cell types present. These results indicate that alterations in hormone release caused by these modulatory factors may in part be due to changes in the ratios of cells committed to the secretion of each hormone. Moreover, the reciprocal nature of these shifts suggests that an interconversion of one cell type to another may have occurred.