In Vivo Comparison of LH-RH and FSH-RH Activities of [DES-GLY 10 ] [PRO 9 -Ethylamide]-LH-RH,[DES-GLY 10 ][PRO 9 -Propylamide]-LH-RH,and LH-RH Using Immature Male Rats 1

Abstract

Summary

The LH-RH and FSH-RH activities of the synthetic LH-RH decapeptide, [Des-Gly¹⁰] [Pro⁹-ethylamide]-LH-RH (EA-LH-RH) and [Des-Gly¹⁰] [Pro⁹-pro-pylamide]-LH-RH (PA-LH-RH) were evaluated using immature male rats. A sc injection of 70 ng or 100 ng of EA-LH-RH induced a greater rise in serum LH and FSH levels than did these doses of LH-RH, but the pattern of changes in serum LH and FSH levels was similar. Elevation of serum LH and FSH levels after injection of 100 ng of PA-LH-RH was more prolonged than after the same dose of EA-LH-RH or LH-RH. The highest levels of LH were observed after EA-LH-RH. Peak FSH levels in response to EA-LH-RH and PA-LH-RH were similar and considerably higher than those after LH-RH. The intergrated amounts of LH released after 100 ng of EA-LH-RH and PA-LH-RH were similar and approximately 5.5 times greater than those after 100 ng of LH-RH. The integrated amounts of FSH released after 100 ng of EA-LH-RH and PA-LH-RH were approximately 7 and 9.4 times greater than those after LH-RH, respectively. Thus, EA-LH-RH and PA-LH-RH have been shown to release more gonadotropins than does LH-RH, and, in addition, administration of PA-LH-RH exhibits a more prolonged effect.

The authors wish to express thanks to Dr. Abba J. Kastin for his help in preparing the manuscript, and to Mr. L. Garcia, Mrs. J. Gauthier and Mrs. M. Essinger for their excellent technical assistance.