Localization and the possible role of plasminogen activators and inhibitors in early stages of placentation

The distribution of mRNAs of tissue type (t) and urokinase type (u) plasmin ogen activator (PA) plus their corresponding inhibitors, type-1 (PAI-1) and type-2 (PAI-2) have been studied in the tissues of human first and second trimester placentae by in situ hybridization. The results show that: (i) Al l the molecules, tPA, uPA, PAI-1 and PAI-2, were identified in the blood ve ssels, the majority of extravillous trophoblastic cells of the decidual lay er between Rohr's and Nitabuch's stria and in the trophoblast cells lining the chorionic plate, basal plate, intercotyledonary septae and cytotrophobl ast cells of the chorionic villous tree. (ii) No expression of such probes was observed in the basal and chorionic plate, glandular cells of the decid ua, the septal tissues or the villous core mesenchyme. The co-distribution of the molecules observed suggests that the co-ordinated expression of the activators and inhibitors in various cells of the placental tissue may play a role in angiogenesis related to conversion of spiral arteries into utero -placental arteries and establishment of a chorio-decidual blood flow durin g early stages of placentation.