Mammalian gonadotropin-releasing hormone (GnRH, pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg- Pro-Gly-NHz), first isolated and characterized by Matsuo et al.'and by Burgus et a1., 2 is well- known to exert regulatory control over reproductive functions. Since ita discovery, thousands of GnRH analogues have been synthesized in a wide-ranging search for potent and long- acting agonists and antagonists for use as therapeutic agents for endocrine diseases and ...