Luteinizing hormone-releasing hormone (LH-RH) activity of some synthetic polypeptides. I. Fragments shorter than decapeptide

Abstract

Summary The luteinizing-releasing hormone (LH-RH) activity of II synthetic polypeptides, some of which were speculatively reported as having LH-RH activity, was assayed in vivo and in vitro against pure natural and synthetic LH-RH. In vivo tests showed that (pyro)Glu-Tyr-Arg-Trp-NH 2 had only 1 part in 7800 of the activity of the LH-RH decapeptide. (Pyro) Glu-Val-Ser-NH 2 , (pyro)Glu-Ser-Val-NH 2 and (pyro)Glu-Gln-Ala-NH 2 , were inactive in vivo in doses as high as 5 – 20 μg/rat. Synthetic (pyro)Glu-His-Pro-amide (thyrotropin-releasing hormone) and a synthetic decapeptide proposed as growth-hormone-releasing hormone showed no LH-RH activity in doses up to 100 μg. N-terminal tripeptide and tetrapeptide fragments of LH-RH as well as the C-terminal octapeptide of LH-RH were also inactive. The C-terminal nonapeptide had an extremely low LH-RH activity (about 1 part in 50,000). The structure-activity relationship of LH-RH has been briefly discussed.