Endothelin A and B receptors change their expression levels during development of human placental villi

Endothelin receptors hale recently been found in non-vascular tissues inclu ding the human placenta. The present study investigated developmental chang es in location and expression levels of endothelin A and B receptors (ETA-R , ETB-R) in human placentae and isolated trophoblast by comparing first and third trimester tissues. In the first trimester all cells and tissues were immunolabelled for ETA-R and ETB-R, whereas in third trimester placentae t he syncytiotrophoblast (ETA-R, ETB-R) and macrophages (ETA-R) were unstaine d. Immunoblotting for both receptors revealed up to three bands at 33-35, 5 0 and 75 kDa, respectively, which were differentially present in the first and third trimester. Pre-adsorption of antibodies with oligopeptides used f or antigen-generation weakened the immunoreactions. ETA-R protein levels de creased (P<0.05) in total villous tissue and isolated trophoblast, whereas ETB-R was unchanged. ETB-R transcripts (RT-PCR) prevailed in both stages an d tissues, but in contrast to the protein levels its preponderance decrease d from first trimester to term in villous tissue (P<0.01), because of a fou r to five-fold increase in ETA-R and only a tn a-fold (P<0.05) increase in ETB-R mRNA levels (P<0.01). We conclude that ET receptor location, intracel lular processing and expression levels in human villous tissue change betwe en the first and third trimester. This may reflect changing functions of ET -I during placental development. (C) 2000 Harcourt Publishers Ltd.