Localization of endothelin-1-like immunoreactivity in human placenta

We examined the distribution of endothelin-1-like immunoreactivity in human placenta, using the immunoperoxidase technique. A specific polyclonal antibody to endothelin-1 was raised in rabbits, which recognized endothelin-1 and its precursor molecule, big endothelin. Immunoperoxidase staining revealed that endothelin-1-like immunoreactivity was widely distributed in the placenta. Endothelin-1-like immunoreactivity was present in endothelial cells of capillaries of the microvilli and in small- and medium-sized arteries and veins. The distribution of endothelin-1-like immunoreactivity was similar to the distribution of Factor VIII-related antigen, which stains endothelial cells. The nature of endothelin in the human placenta was further examined with cultured umbilical vein endothelial cells. Endothelial cells released endothelin-like material into the culture medium. The amount of endothelin-like material varied directly with time of incubation and the amount of fetal calf serum in the culture medium. Fractionation of the endothelin-1-like material by reversed-phase high-performance liquid chromatography (HPLC) and quantitation by radioimmunoassay (RIA) revealed that endothelin-like immunoreactivity co-eluted with endothelin-1 but not with big endothelin-1. We conclude that endothelin-1-like immunoreactivity is widely distributed in vascular endothelium of the human placenta. These data are compatible with a role for endothelin as an autocrine or paracrine modulator of vascular tone in the human placenta.