Rapid clearance of D-Ala(6),Pro(9)NEt mammalian gonadotropin releasing hormone from Chinook salmon plasma

Chinook salmon Oncorhynchus tshawytscha were injected with D-Ala(6),Pro(9)N Et mammalian gonadotropin releasing hormone (GnRHa) at 5 mu g/kg body weigh t, a typical dose administered to promote ovulation or spermiation. Followi ng this injection, salmon were sampled serially, and plasma GnRHa levels we re determined by chromatography and radioimmunoassay. Plasma levels of GnRH a were elevated following injection (>500 pg/mL), then levels declined rapi dly and were nondetectable in all fish by 5 h postinjection. Using nonlinea r regression, the data were fitted to an exponential decay model, which cal culated a plasma half-life of 0.8 h, with a 95% confidence interval of 0.5- 5.8 h. These studies provide further evidence of the rapid clearance of GnR Ha, when used for the acceleration of final sexual maturation.