Use of a mammalian gonadotropin‐releasing hormone (Gn RH ) agonist to characterize pituitary G n RH receptors in white sturgeon ( A cipenser transmontanus R ichardson)

Summary Aim of the present study was to characterize the pituitary Gn RH receptor in white sturgeon, Acipenser transmontanus , using a superagonist analog of mammalian Gn RH [ D ‐ A la 6 , des ‐ G ly 10 – P ro 9 ]‐ethylamide and to investigate the possible effect of estradiol‐17β treatment on the concentration and affinity of the Gn RH receptor in immature white sturgeon. The binding of 125 I ‐ G n RH ‐ A to sturgeon pituitary receptors was rapid and saturable at 4°C and 20°C. However, maximal binding at 20°C was almost two‐fold greater than the highest binding noted at 4°C. Specific binding of radioligand was directly related to the amount of tissue included in the assay system over the range of 5–20 mg fresh tissue equivalents per ml. The binding capacity of 125 I ‐ G n RH ‐ A with sturgeon pituitary tissue was much greater than radiolabeled G n RH . Administration of E 2 to immature sturgeon caused an almost two‐fold increase in G n RH ‐ A binding capacity ( E 2 treated: B max = 2.87 fmoles 3 mg −1 FTE ; control: B max = 1.70 fmoles 3 mg −1 ), and did not affect Gn RH ‐A binding affinity (E 2 treated: Ka = 0.13 × 10 11   m −1 ; control: Ka = 0.15 × 10 11 m −1 ). Overall, the study provides evidence that the Gn RH analog is effective for characterizing the G n RH receptor in white sturgeon; however, more experimentation is necessary to determine whether E 2 administration to immature white sturgeon can increase the G n RH receptor capacity.