Effects of estrogen and epidermal growth factor on prolactin and Pit-1 mRNA in GH3 cells

The effects of epidermal growth factor (EGF) and 17 beta-estradiol (E2) on the expression of prolactin (PRL), the transcription factor Pit-1/GHF-1 (Pit-1), and on dopamine D2 receptor mRNA in GH3 cells were analyzed by immunocytochemistry, in situ hybridization, and Northern analysis in a defined serum-free cell culture medium. Radioimmunoassay was used to determine PRL secretion. Both EGF and E2 stimulated PRL mRNA and PRL secretion, although the effects of EGF were more rapid than those of E2. Pit-1 mRNA levels were not significantly changed in spite of the 2- to 8-fold increases in PRL mRNA levels and significant increases in PRL secretion. Analysis of dopamine D2 receptor mRNA by in situ hybridization and Northern hybridization detected expression of dopamine receptor in GH3 cells, but the receptor mRNA levels were not modified by EGF or E2 treatment in complete serum or in serum-free media. These observations suggest that EGF and E2 modulate PRL mRNA levels and PRL secretion significantly in vitro, while the mRNA levels of Pit-1 do not change significantly in GH3 cells cultured in a defined culture medium.