Receptors and neurosecretory actions of endothelin in hypothalamic neurons

Primary cultures of rat hypothalamic neurons were found to secrete the potent calcium-mobilizing and mitogenic peptide endothelin (ET) and to contain specific ET binding sites with higher affinity for ET-1 and ET-2 than ET-3. ET receptors of similar specificity were also identified in two gonadotropin-releasing hormone (GnRH) neuronal cell lines (GT1-1 and GT1-7). In both primary cultures and GnRH neurons, receptor binding of ETs led to marked and dose-dependent increases of inositol phosphates; inositol bis-, tris-, and tetrakisphosphates increased promptly, reached a peak within 2 min, and returned toward the steady-state levels during the next 10 min. ET-1 was more potent than ET-3 in mobilizing inositol phosphates, consistent with its greater affinity for the ET receptors in these cells. ET also stimulated GnRH secretion from perifused hypothalamic cultures and GnRH cell lines, with a sharp increase followed by a prompt decline to the basal level. These data show that ET is produced in the hypothalamus and acts through calcium-mobilizing ET receptors in normal and transformed secretory neurons to stimulate GnRH release. These actions of locally produced ETs upon GnRH-secreting neurons indicate that the vasoconstrictor peptides have the capacity to regulate neurosecretion and could participate in the hypothalamic control of anterior pituitary function and gonadotropin secretion.