Binding affinity and biological activity of gonadotropin-releasing hormone analogs in the African catfish, Clarias gariepinus

Abstract Salmon gonadotropin-releasing hormone (sGnRH), its analog D-Arg 6 -Pro 9 -sGnRH-NEt (sGnRHa) and the luteinizing hormone-releasing hormone (LHRH) analogs D-Ser(t-Bu) 6 -Pro 9 -LHRH-NEt (Buserelin) and D-Ala 6 -Pro 9 -LHRH-NEt (LHRHa) were tested for their biological activity in the African catfish, Clarias gariepinus . sGnRHa and Buserelin had similar GTH-releasing potencies in vitro and in vivo and were found to be more active in stimulating GTH release than sGnRH and LHRHa. sGnRH was found to be the least potent GTH-releasing peptide. GnRH receptor displacement experiments at 4°C and 25°C, the latter being the physiological temperature of the catfish, showed a sequence of relative binding affinities of sGnRHa>sGnRH>Buserelin>LHRHa. In addition, sGnRHa and Buserelin were found to be the most stable GnRH agonists. These results indicate that the degradation rate of the GnRH peptides might be the primary factor determining their bioactivity in the African catfish.