2 SUBTYPES OF ENDOTHELIN RECEPTORS AND ENDOTHELIN PEPTIDES ARE EXPRESSED IN DIFFERENTIAL CELL-TYPES OF THE RAT PLACENTA - IN-VITRO RECEPTORAUTORADIOGRAPHIC AND IN-SITU HYBRIDIZATION STUDIES

We studied the localization of endothelin (ET) receptors and ET peptid es in the rat placenta. In vitro receptor autoradiographic and in situ hybridization studies revealed the differential and cell-specific dis tribution of ET receptor subtypes, suggesting that each ET receptor pl ays a different role in the function of the placenta. The expression o f the ET(B) receptor was concentrated to cytotrophoblasts and trophobl astic giant cells of the basal zone, in which fetal cells directly fac e maternal cells. The ET(A) receptor was confined to the decidual tiss ue and vascular wall. Both ET receptors coexisted in the labyrinth in an approximately 50:50 ratio. Prepro-ET-1 messenger RNA (mRNA) was det ected in cytotrophoblasts and trophoblastic giant cells of the basal z one and endothelial cells of vessels, whereas ET-1-like immunoreactivi ty was present not only in trophoblasts and endothelial cells, but als o in the decidual tissue and vascular wall. ET-3 mRNA was localized in migrating cells. We also found changes in the expression levels of ET receptors by means of a cold ligand saturation study. The number of s pecific [I-125]ET-1-binding sites was increased in the basal zone and labyrinth with gestation, but not in the decidual tissue. The enhancem ent of ET(A) receptor, ET(B) receptor, and prepro-ET-1 mRNA levels was also supposed, based on data obtained by RT-PCR Southern hybridizatio n. On the other hand, ET-3 mRNA levels were reduced with gestation. Th ese findings support the idea that ETs, through interaction with ET(A) and ET(B) receptors, play an important role in the regulation of plac ental growth and fetoplacental circulation through autocrine and parac rine mechanisms.