The 125I-labeled endothelin-1 ([125I]ET-1) binding sites in microvillous membranes from early gestation and term human placentas were investigated. The Kds for [125I]ET-1 binding to early gestation (68 +/- 15 pmol/l) and term (45 +/- 8 pmol/l) microvilli (n = 4) were not significantly different. The density of binding sites decreased significantly, from 243 +/- 80 fmol/mg protein in early gestation microvilli to 54 +/- 10 fmol/mg protein in term microvilli. The endothelin (ET) receptor (ET-R) subtype profiles were determined by competition binding studies with unlabeled ET-1, ET-3, and selective agonists and antagonists for ETA-R and ETB-R. In early gestation placental microvilli, we observed the presence of 72%) ETB-R, (mainly ETB2-R subtype), and 28%. ETA-R. Only ETB-R (mainly the ETB2-R subtype) was present in term placental microvilli. We suggest that the ETB-R on the placental microvillous membrane is involved in specific trophoblastic functions and may play a major role in ET clearance by modulating the amounts of ETs in the maternal intervillous blood space.
F Mondon, A Anouar and F Ferre
ML Raffin-Sanson, F Ferre, J Coste, C Oliver, D Cabrol and X Bertagna
OBJECTIVE: The human placenta normally expresses the pro-opiomelanocortin (POMC) gene. The pattern and secretory kinetics of POMC and/or POMC-derived peptides by the placenta during gestation is still debated. We recently demonstrated that full length POMC was a normal product of the human placenta. The aim of our study was to establish its normal secretory kinetics and to explore its physiological relevance. DESIGN: In a prospective, longitudinal study, thirty normal pregnant women had monthly measurements of plasma POMC. In a cross-sectional study of 128 healthy pregnant women, plasma POMC and human chorionic gonadotrophin (hCG) were concomitantly measured to assess their correlation. Finally, POMC levels were assessed in venous and arterial cord blood samples, in amniotic fluid and in retroplacental blood. METHODS: Plasma POMC was measured by a specific IRMA in unextracted blood or biological fluid. RESULTS: Plasma POMC became detectable by the 8th week of pregnancy and reached its maximum at around the 20th week, remaining stable thereafter. The relationship between POMC and gestation time (weeks) best fitted with a third degree polynomia curve. A significant negative correlation (P=0.01) was observed between plasma levels of POMC and hCG after adjustment for gestation time to take into account the dependence of both hormones on this parameter. POMC was not secreted into the fetal circulation at term, but was present in very high levels in amniotic fluid. The highest levels of POMC were present in the retroplacental blood where the values were 35 times higher than in maternal blood; by comparison, corticotrophin releasing hormone and ACTH values in this compartment were twice or equal to those in the maternal blood. CONCLUSION: Placental POMC secretion increases during the first half of pregnancy and reaches a plateau from the 20th week to delivery. The inverse correlation between POMC and hCG plasma levels, and very high POMC levels at the feto-maternal interface suggest a physiological role for this precursor during pregnancy.
I Eude, E Dallot, MC Vacher-Lavenu, C Chapron, F Ferre and M Breuiller-Fouche
OBJECTIVE: Factors responsible for the abnormal proliferation of myometrial cells that accompanies leiomyoma formation are unknown, although steroid hormones and peptide growth factors have been implicated. We hypothesized that endothelin-1 (ET-1) is a physiological regulator of tumor growth. DESIGN: In this study, we investigated the role of ET-1 on growth of human leiomyoma cells and its synergistic effect with growth factors, as well as the signaling pathway involved in this interaction. METHODS: Leiomyoma cell proliferation was assayed by [H]thymidine incorporation and cell number. Protein kinase C (PKC) isoforms were analyzed by Western blot using specific antibodies. RESULTS: ET-1 on its own was unable to stimulate DNA synthesis but potentiated the leiomyoma cell growth effects of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), IGF-I and IGF-II. The failure of a protein tyrosine kinase (PTK) inhibitor, tyrphostin 51, to affect the potentiating effect of ET-1, supports the hypothesis of non-involvement of PTK in this process. The inhibition of PKC by calphostin C or its down-regulation by phorbol 12,13-dibutyrate (PDB) eliminated the potentiating effect of ET-1, but did not block cell proliferation induced by the growth factors alone. Five PKC isoforms (alpha, beta1, epsilon, delta and zeta) were detected in leiomyoma cells, but only phorbol ester-sensitive PKC isoforms (PKCalpha, epsilon and delta) contribute to the potentiating effect of leiomyoma cell growth by ET-1. CONCLUSIONS: We have demonstrated that ET-1 potentiates leiomyoma cell proliferation to growth factors through a PKC-dependent pathway. These findings suggest a possible involvement of ET-1 in the pathogenesis of leiomyomas.