Binding capacity of luteinizing hormone-releasing hormone and its analogues for pituitary receptor sites.

Competition for luteinizing hormone-releasing hormone (LH-RH) receptor sites by the inhibitory analog D-Phe², D-Trp³, D-Phe⁶]-LH-RH and by the superactive stimulatory analog D-Trp⁶]-LH-RH was observed in adenohypophysial homogenates incubated at 4°C. Competition for LH-RH binding sites was less evident with adenohypophysial plasma membranes. The binding affinities of these analogues to LH-RH pituitary receptors can explain at least in part their respective action in blocking ovulation and in inducing a greater release of luteinizing hormone and follicle stimulating hormone than the parent hormone.