Expression and biological effects of endothelin-1 in human gonadotropin-releasing hormone-secreting neurons

In a previous report, we demonstrated that in FNC-B4 cells, derived and cha racterized from a human fetal olfactory epithelium, both sex steroids and o dorants regulate GnRH secretion. We now report the presence and biological activity of endothelin (ET)-1 in this GnRH-secreting neuronal cell. By in s itu hybridization and immunohistochemistry, we found gene and protein expre ssion of ET-1 and its converting enzyme ECE-1 in both fetal olfactory mucos a and FNC-B4 cells. The presence of authentic ET-1 in the conditioned media of FNC-B4 cells was further supported by combined RL4s and highperformance liquid chromatography studies. Experiments with radiolabeled ET-1 and ET-3 strongly indicated the presence of two classes of binding sites, correspon ding to the ETA (16,500 sites/cell) and the ETB receptors (8,700 sites/cell ). Functional studies, using selective analogs, indicated that these two cl asses of receptors subserve distinct functions in human GnRH-secreting cell s. The ETA receptor subtype mediated an increase in intracellular calcium a nd GnRH secretion. Conversely, stimulation of the ETB subtype induced DNA s ynthesis and mitogen-activated protein kinase p44(ERK1) :II expression. Thi s is the first demonstration, in a human in vitro model, of a neuroendocrin e role for ET-1 as regulator of GnRH-secreting neuron activity.