Corticosteroids stimulate the differentiation of growth hormone cells but suppress that of prolactin cells in the fetal rat pituitary.

An organ culture study was carried out to examine the effects of adrenal corticosteroids on the development of growth hormone (GH) cells and prolactin (PRL) cells. The adenohypophysial primordia were separated from 13.5-day-old fetal rats and maintained in vitro for 8 days with or without cortisol. Immunohistochemical examination of these explants showed that cortisol stimulated the differentiation of GH cells but suppressed that of PRL cells in a dose-dependent manner. In the absence of cortisol there were more PRL cells. Corticosterone had a similar effect on the developing adenohypophysis. When the pituitary primordia of Day 16.5 were cultured for 5 days and studied by the in situ hybridization technique, the expression of GH and PRL mRNA was found to be parallel with the immunoreactivity of the respective hormones. These data are discussed in relation to the normal development of GH and PRL cells in the fetal rat adenohypophysis.