COLOCALIZATION OF DOPAMINE D-1 AND D-2 RECEPTOR MESSENGER-RNAS IN RATPLACENTA

Dopamine is present in the human placenta. The major function of dopam ine is the inhibition of human placental lactogen (hPL) release from h uman trophoblastic cells. This effect is mediated by cAMP through dopa mine D-2, receptors. However, studies on the effects of cAMP in the co ntrol of hPL release have yielded conflicting results, The purpose of this study is to explore the distribution of dopamine receptors in the rat placenta. Dopamine D-1, and D-2, receptor mRNAs were colocalized in the rat placenta by in situ hybridization histochemistry using radi olabeled cRNA probes. Dopamine D-1, and D-2, receptor mRNAs were detec ted in large cells of the endometrium of the uterus on day 10 of gesta tion. On days 12-16 of gestation, hybridization signals were localized mainly in the spongiotrophoblast and giant cells of the junctional zo ne of the placenta. With the development of the placenta, signals were moving from the junctional zone to the labyrinth zone. Pit-1 mRNA was detected in the placental lactotrophs and was also colocalized in nei ghboring placental sections. Our results clearly showed that dopamine D-1, and D-2, receptor mRNAs were coexpressed in the placental lactotr ophs that express Pit-1 mRNA.