Detection of a potential progenitor cell in the human fetal pituitary that secretes both growth hormone and prolactin.

The structural similarities between human PRL (hPRL) and human GH (hGH) suggest a common evolutionary origin of the two hormones. The existence of these similarities also suggests the existence of a developmental intermediate cell type which has the potential to produce and secrete both hPRL and hGH. We have applied reverse hemolytic plaque assays to monitor the secretions of individual fetal human pituitary cells to determine if any of these cells secrete both hPRL and hGH. When hPRL and hGH assays were performed sequentially on cells obtained from five fetuses of 18-22 weeks gestational age, we consistently found a subpopulation of cells that formed plaques in both assays, i.e. they secreted both hPRL and hGH. The majority of fetal cells secreting hPRL also secreted hGH at this stage of development. These data were corroborated with light and electron microscopic immunocytochemical localization of hPRL and hGH in a subpopulation of previously identified fetal somatotrophs. These findings suggest that in addition to the classical somatotrophs and lactotrophs, the fetal human pituitary contains an additional cell type which secretes both hPRL and hGH. The dual hormone-secreting cell may represent a common progenitor of these classical cell types. It also may be the cell of origin of those pituitary tumors that secrete both PRL and GH.