CHARACTERIZATION AND LOCALIZATION OF GONADOTROPIN-RELEASING-HORMONE RECEPTORS IN THE ADULT FEMALE SEA LAMPREY, PETROMYZON-MARINUS

Quantitative in vitro autoradiography was used to characterize and localize putative GnRH receptors in the anterior pituitary of the adult female sea lamprey, Petromyzon marinus. Pituitaries were sectioned at 20 mu m and incubated for 3 h at 4 C with DAla(6),Pro(9) NEt mammalian GnRH as both the labeled and unlabeled ligand. Scatchard analysis revealed two classes of high affinity binding sites with K-dS of 1.5 X 10(-12) M and 5 x 10(-9) M. Binding to the GnRH receptors was saturable, reversible, tissue specific, and time and temperature dependent. Displacement studies showed that labeled peptide could be displaced by chicken GnRH-I, chicken GnRH-II, synthetic mammal, salmon, lam prey GnRH-I, lamprey GnRH-III, DAIa(6),Prog NEt mammalian GnRH and DPhe(2,6),Pro(3) lamprey GnRH. The proximal pars distalis region of the anterior pituitary contained most of the GnRH binding sites with slight binding in the rostral pars distalis. These data provide direct evidence of GnRH activity on the Agnathan pituitary and are the first to demonstrate that a vertebrate pituitary contains two high affinity binding sites for GnRH.