Inhibition of the activity of the luteinizing hormone-releasing hormone (LH-RH) by analogues with variations at positions 2, 3, and 6 and the carboxyl terminus.

In the isolated rat pituitary assay, [Thr2,Leu3]-LH-RH, [Leu2,Ala3,D-Ala6]-LH-RH, and des-Gly10-[Abu2,Ala3,D-Ala6]-LH-RH ethylamide inhibited the LH release due to 0.3 ng/mL of added LH-RH at a 10 microgram/mL dosage. Under these same assay conditions, des-Gly10-[Ile2,Ala3,D-Ala6]-LH-RH ethylamide was about one-tenth as active, and no inhibition was observed by [Leu2,Ser3]-LH-RH or [Leu2,Asn3]-LH-RH at a 100 microgram/mL dosage. The corresponding results from FSH inhibition assays, in vitro, are also reported.