In vivo activity of salmon gonadotropin releasing hormone (GnRH), its agonists with structural modifications at positions 6 and 9, mammalian GnRH agonists and native cGnRH-II on the spawning of an Indian catfish

Effects of the native GnRHs and various agonists have been evaluated on the spawning of an Indian catfish, Heteropneustes fossilis. This study tested salmon (s) GnRH agonists and mammalian (m) GnRH agonists where a D-amino ac id residue was substituted alone at position 6 or the C-terminal was modifi ed with ethylamide. GnRH agonists with a combination of these structural mo difications were also evaluated separately for their effect on the spawning of the catfish. Native sGnRH, [Pro(9) NEt]-sGnRH agonist and chicken (c) G nRH-II exhibited similar activity and induced spawning within 14-18 h at a dose of 100 mu g kg(-1) body weight (BW). [D-Lys(6)]-sGnRH agonist and [D-L ys(6) Pro(9) NEt]-sGnRH agonist, induced spawning at a dose of 100 mu g kg( -1) BW and 1 mu g kg(-1) BW, respectively. The most notable observation in this study was the ineffectiveness of [D-Ala(6)]-mGnRH agonist and [Des Gly (10) D-Ala (6) Pro(9) NEt]-mGnRH agonist. The results obtained suggest that substitution at position 6 alone, and in conjunction with an ethylamide-ba sed modification at the C-terminal in the native sGnRH structure, increases the potency of the tested agonists to induce spawning in the catfish. This study also discusses the potential use and incorporation of cGnRH-II for t he development of more generic spawning induction therapies.