Cellular localization of human relaxin-like factor in the cyclic endometrium and placenta

We have studied the cellular localization of the relaxin-like factor (RLF) in the histologically normal cyclic endometrium collected from days 3-26 of the menstrual cycle. RLF transcripts and protein were detected in the lumi nal and glandular epithelium and in stromal cells at all stages of the cycl ic endometrium. Increased expression of RLF was observed in endometrial tis sues in the proliferative as compared to the secretory phase, suggesting th at oestrogens affect RLF gene activity in the human endometrium. The cellul ar localization of RLF transcripts and protein was also determined in first trimester placental tissues obtained from normal and ectopic tubal implant ation sites and in third trimester placentae of normal and pre-eclamptic pr egnancies. In first trimester placenta, weaker expression of RLF was observ ed in the syncytiotrophoblast as compared to the underlying cytotrophoblast . Extravillous trophoblast cells constitutively expressed RLF. Trophoblast cells were the main source of RLF in the human placenta and trophoblastic R LF gene activity was unaffected by either the site of implantation or the i nvasive properties of the cytotrophoblast as demonstrated by samples from p atients with tubal implantation and pre-eclampsia respectively. Decidual ce lls weakly expressed RLF. The presence of unprocessed and cleaved immunorea ctive RLF in term placenta was determined by Western analysis. The above re sults suggest a functional role for both RLF isoforms within normal placent al tissue.