Inhibitory analogues of the luteinizing hormone-releasing hormone having D-aromatic residues in positions 2 and 6 and variation in position 3.

A single sc injection of 750 microgram/rat of [D-Phe2,Pro3,D-Phe6]-LH-RH on proestrus completely inhibited ovulation in 4-day cycling rats. Ovulation was inhibited partially at 375 microgram/rat. At the 720 microgram/rat dosage, analogues of LH-RH with D-Phe in positions 2 and 6, and with Sar, Arg, or Hyp in position 3, resulted in partial inhibitors and an inactive analogue with Thr substitution. In the same assay, analogues with D-Phe in position 2 and D-Trp in position 6 were partial inhibitors when D-Phe, Met, or Val were in position 3 and inactive with Ile substitution.