Homologous regulation of gonadotropin-releasing hormone receptors in cultured pituitary cells.

Specific receptors for gonadotropin-releasing hormone (GnRH) in cultured rat pituitary cells were increased by subnanomolar concentrations of GnRH agonists and decreased by high concentrations of these peptides. The antagonist [D-Phe2, Pro3, D-Phe6]GnRH did not alter GnRH binding capacity and blocked the increase in sites induced by GnRH. These findings provide direct evidence for the homologous regulation of GnRH receptors by physiological concentrations of the hypothalamic peptide, an action that could mediate the cyclical and postcastration increases in GnRH receptors and responsiveness of the pituitary gonadotrophs.