ESTRADIOL-POSITIVE FEEDBACK ON GONADOTROPIC (GTH) CELLS IN FRESHWATER MALE SILVER EELS

Freshwater male silver eels injected with estradiol-17β for 20 and 40 days show a hypertrophy, an increased vacuolar content, and a glycogen depletion of the liver. In the strongly opalescent plasma, a fact probably due to the presence of vitellogenin, sodium is slightly decreased, calcium is considerably increased. When eels are sacrificed 40 days after the end of the treatment, these changes partly regress, values being not yet normalized. A few unusual oocytes are present in the organs of Syrski. In the pituitary, prolactin (PRL)- and growth hormone (STH)-secreting cells are stimulated. Gonadotrophs (GTH) are enlarged and differentiated, containing abundant coarse glycoprotein granules. MSH cells appear less active, and PAS-positive cells of the pars intermedia are degranulated. After 40 days without treatment, these responses disappear or at least are greatly reduced, GTH cells being significantly smaller and less granulated. These data are briefly compared with those previously obtained in female eels. They show that estradiol (E2) acts on GTH cells to stimulate hormonal synthesis by a positive feedback. This simple low-cost technique producing large amounts of eel GTH will help to study its biological activity and may facilitate the induction of sexual maturation of the eel normally obtained with heterologous gonadotropins. © 1979.