Insect oostatic activity of GnRH and its fragments

Mammal, ¹²⁵I-mammal, salmon, chicken I and II GnRHs and three fragments of mammal GnRH were synthesized and their effect on oogenesis in the flesh fly Neobellieria(formerly Sarcophaga) bullata (Diptera) was investigated. The peptides were prepared by the Merrifield solid phase synthesis on polystyrene/divinylbenzene polymer using the N-Boc strategy in DMF and were purified by preparative RP-HPLC in a gradient of water-MeOH. From the peptides assayed, only mammal GnRH and two of its carboxy-terminus truncated analogs remarkably affected the processes of egg development in ovarioles, causing changes in the follicular epithelium, proliferation of its nuclei and cell division towards the inner part of the egg chamber. The process led to the occurrence of multinuclear follicular epithelium which finally filled up almost the whole egg chamber and then it degenerated. The inability of GnRH of other animal species to evoke the changes in the egg development establishes the question of primary structures of GnRH responsible for these biological effects. The identityof sequences of GnRHs from position 1 up to 6 (with the exception of chicken GnRH II) points to functionality of amino acids located in positions 7 and 8 of the peptide chain. The radioactivity of the ¹²⁵I-labelled mammal GnRH with maintained oostatic activity and its receptor competition with the non-labelled mammal GnRH were measured in selected insect organs and exhibited different residual values according to the organ and the time after applicationof the peptide. A transfer of the radioactivity into the next (F₁) generation was also observed.