EFFECTS OF DOPAMINE AND ESTROGEN ON THE REGULATION OF PIT-1-ALPHA, PIT-1-BETA, AND PL-II GENE-EXPRESSION IN THE RAT PLACENTA

Pituitary-specific transcription factor Pit-1 regulates growth hormone and prolactin gene expression in the pituitary, Recently, Pit-1 was s hown to be locally synthesized in the rat placenta and is involved in the regulation of rat placental lactogen (PL) gene expression. Pit-1 h as three different splicing variants. They are well known as being bio logically active. In the present study, we found that Pit-1 beta is al so synthesized in the rat placenta and we tried to examine the effects of dopamine and estrogen on the regulation of Pit-1 alpha, beta and P L-II genes expression using the reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot hybridization, A dopamine recepto r agonist, bromocriptine, significantly decreased placental Pit-1 alph a, beta, and PL-II mRNA levels. To examine the effect of estrogen on t he gene expression of Pit-1 beta, pregnant female rats were ovariectom ized (OVX) and injected daily with 17 beta-estradiol, OVX markedly low ered the amount of Pit-1 beta mRNA, Estrogen injection recovered the O VX-induced inhibition of Pit-1 beta mRNA level, Finally, we investigat ed the site-specific transcription of Pit-1 alpha and beta mRNA in the labyrinth zone and junctional zone of the placenta in 15 and 20 days of gestation. The main site of Pit-1 alpha and beta synthesis was shif ted from the junctional zone to the labyrinth zone from 15 to 20 days of gestation. Together, these data presume that Pit-1 beta may play a more important role in the placenta than in the pituitary and that Pit -1 may be involved in the regulation of the PL and prolactin-like pept ide by estrogen and dopamine in the rat placenta.