Characterization of gonadotropin-releasing hormone binding sites in the pituitary of the three-spined stickleback, Gasterosteus aculeatus

Abstract

Binding sites for gonadotropin-releasing hormone (GnRH) in stickleback pituitary homogenates were characterized using an iodinated, superactive analog of salmon GnRH (sGnRH), d-Arg 6-Pro 9-sGnRH-NEt (sGnRHa). Binding of 125I-sGnRHa reached equilibrium after 60 min incubation at 4° and was a function of tissue concentration. The specificity of 125I-sGnRHa binding was demonstrated by displacement with sGnRHa, sGnRH, and Buserelin [ d-Ser(t-Bu) 6-Pro 9-GnRH-NEt]. Both Scatchard analyses of saturation data and displacement curves revealed a single class of high-affinity binding sites ( K a = 0.71 ± 0.03 × 10 9 M −1, B max = 1087 ± 165 fmol/mg protein).