THE CHICKEN PITUITARY-SPECIFIC TRANSCRIPTION FACTOR PIT-1 IS INVOLVED IN THE HYPOTHALAMIC REGULATION OF PITUITARY HORMONES

Pit-1 is a pituitary-specific POU-domain DNA binding factor, which binds to and trans-activates promoters of growth hormone- (GH), prolactin- (PRL) and thyroid stimulating hormone-beta- (TSHβ) encoding genes. Thyrotropin-releasing hormone (TRH) is located in the hypothalamus and stimulates TSH, GH and PRL release from the pituitary gland. In the present study, we successfully used the cell aggregate culture system for chicken pituitary cells to study t he effect of TRH administration on the ggPit-1* (chicken Pit-1), GH and TSHβ mRNA expression in vitro. In pituitary cell aggregates of 11-day-old male broiler chicks the ggPit-1* mRNA expression was significantly increased following TRH administration, in- dicating that the stimulatory effects of TRH on several pituitary hormones are mediated via its effect on the ggPit-1* gene expression. Theref ore, a semi- quantitative RT-PCR method was used to detect possible changes in GH and TSHβ mRNA levels. TRH affected both the GH and TSHβ mRNA levels. The re- sults of this in vitro study reveal that ggPit-1* has a role in mediating the stimula- tory effects of TRH on pituitary hormones like GH and TSHβ in the chicken pi- tuitary.