Response to thyrotropin-releasing hormone (TRH) on prolactin promoter activity in TRH-treated cells. GH3 cells were treated or non-treated with 100 nM TRH for 48 hours in 1% fetal bovine serum (FBS)-containing Dulbecco's modified Eagle medium (DMEM). Then, the culture medium was washed with and changed to serum-free DMEM. Next, the cells were stimulated with 100 nM TRH for six hours. Luciferase activity was measured and relative induction is shown (relative to TRH-untreated control set as 1.0). **P < 0.01 versus controls in TRH non-treated cells. The difference between TRH stimulation in non-treated cells and treated cells was not statistically significant.